The Insect World
by Louis Figuier · English · Gutenberg #45596 · 958,187 chars · public domain (US)
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Title: The Insect World
Author: Louis Figuier
Editor: P. Martin Duncan
Release date: May 6, 2014 [eBook #45596]
Most recently updated: October 24, 2024
Language: English
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Transcriber Note
Emphasized text represented as _Italic_.
Whole and fractional part of numbers: 1-3/4.
[Illustration: The Dragon-fly (_Libellula depressa_). A. Perfect Insect.
B. Perfect Insect emerging from the Pupa. C. D. Larvæ and Pupæ.]
THE
INSECT WORLD:
BEING
_A Popular Account of the Orders of Insects_;
TOGETHER WITH
A DESCRIPTION OF THE HABITS AND ECONOMY OF
SOME OF THE MOST INTERESTING SPECIES.
BY
LOUIS FIGUIER.
A New Edition,
REVISED AND CORRECTED BY P. MARTIN DUNCAN, F.R.S.
WITH 579 ILLUSTRATIONS.
D. APPLETON AND CO.,
_NEW YORK_.
PREFACE
This popular French book on Insects has been placed in my hands in
order that the scientific portions of it should be examined and, if
necessary, corrected. This task has been a light one, for the book had
already passed through the able editorship of Mr. Jansen. But I have
added a short notice of the Thysanoptera, which did not appear in M.
Figuier's original work, and also the necessary information respecting
the evolution of Stylops.
P. MARTIN DUNCAN.
LEE, 1872.
CONTENTS.
PAGE
INTRODUCTION 1
APTERA 27
DIPTERA 33
Nemocera 35
Brachycera 47
HEMIPTERA 90
Heteroptera 90
Homoptera 101
LEPIDOPTERA 138
The Larva, or Caterpillar 138
The Chrysalis, or Pupa 146
The Perfect Insect 165
ORTHOPTERA 284
HYMENOPTERA 313
THYSANOPTERA 400
NEUROPTERA 402
COLEOPTERA 435
INDEX 523
THE INSECT WORLD.
INTRODUCTION.
It is not intended to investigate the anatomy of insects in this work
thoroughly; but, as we are about to treat of the habits and economy of
certain created beings, it is necessary first to explain the principal
parts of their structure, and the stages which every perfect insect or
_imago_ has undergone before arriving at that state.
We, therefore, proceed to explain, as simply as possible, the anatomy
of an insect, and the functions of its organs.
If we take an insect, and turn it over, and examine it carefully, the
first thing that strikes us is that it is divided into three parts:
the head; the thorax, or chest; and the abdomen, or stomach.
The head (Fig. 1) is a kind of box, formed of a single piece, having
here and there joints more or less strongly marked, sometimes scarcely
visible. It is furnished in front with an opening--often very
small--which is the mouth; and with some for the eyes, and with others
for the insertion of the antennæ or horns.
[Illustration: Fig. 1.--Head of an Insect]
The integuments of the head are generally harder than the other
parts of the body. It is necessary that this should be so. Insects
often live and die in the midst of substances which offer some
resistance. It is necessary, therefore, that the head should be strong
enough to overcome such resistance. The head contains the masticatory
organs, which, frequently having to attack hard substances, must be
strongly supported. The exception to this rule is among insects which
live by suction.
It would be out of place here to mention the numerous modifications
of the head which are presented in the immense class of insects.
The eyes of insects are of two kinds. There are compound eyes, or eyes
composed of many lenses, united by their margins and forming hexagonal
facettes; and there are also simple eyes, or ocelli.
The exterior of the eye is called the cornea (Fig. 2), each facette
being a cornea; and the facettes, which vary in size even in the same
eye, unite and form a common cornea, which is represented by the
entire figure.
[Illustration: Fig. 2.--A Compound Cornea.]
In order to show the immense number of the facettes possessed by many
insects, we give the following list:--
In the genus Mordella (a genus of beetles) the eye has 25,008 facettes.
In the _Libellula_ (dragon-fly) 12,544 "
In the genus _Papilio_ (a genus of butterflies) 17,355 "
In _Sphinx convolvuli_ (the convolvulus hawk-moth) 1,300 "
In _Bombyx mori_ (the common silkworm moth) 6,236 "
In the house-fly 4,000 "
In the ant 50 "
In the cockchafer 8,820 "
The facettes appear to be most numerous in insects of the genus
_Scarabæus_ (a genus of beetles). They are so minute, that they can
only be detected with a magnifying glass.
Looked at in front, a compound eye may be considered an agglomeration
of simple eyes; but internally this is hardly correct.
On the under side of each facette we find a body of a gelatinous
appearance, transparent, and usually conical; the base of this
occupies the centre of the facette in such a manner as to leave around
it a ring to receive some colouring matter. This body diminishes in
thickness towards its other extremity, and terminates in a point where
it joins a nervous filament proceeding from the optic nerve. These
cones, agreeing in number with the facettes, play the part of the
crystalline lens in the eyes of animals. They are straight and
parallel with each other. A pigment fills all the spaces between the
cones, and between the nervous filaments, and covers the under side of
each cornea, except at the centre. This pigment varies much in colour.
There are almost always two layers, of which the exterior one is the
more brilliant. In fact, these eyes often sparkle with fire, like
precious stones.
M. Lacordaire, in his "Introduction à l'Entomologie," from which we
borrow the greater part of this information, has summed up as follows,
the manner in which, according to M. Müller, the visual organs of
insects operate:--
"Each facette, with its lens and nervous filament, separated from
those surrounding them by the pigment in which they are enclosed, form
an isolated apparatus, impenetrable to all rays of light, except those
which fall perpendicularly on the centre of the facette, which alone
is devoid of pigment. All rays falling obliquely are absorbed by that
pigment which surrounds the gelatinous cone. It results partly from
this, and partly from the immobility of the eye, that the field of
vision of each facette is very limited, and that there are as many
objects reflected on the optic filaments as there are corneæ. The
extent, then, of the field of vision will be determined, not by the
diameter of these last, but by the diameter of the entire eye, and
will be in proportion to its size and convexity. But whatever may be
the size of the eyes, like their fields of vision, they are
independent of each other; there is always a space, greater or less,
between them; and the insect cannot see objects in front of this space
without turning its head. What a peculiar sensation must result from
the multiplicity of images on the optic filaments! This is not more
easily explained than that which happens with animals which, having
two eyes, see only one image; and probably the same is the case
with insects. But these eyes usually look in opposite directions,
and should see two images, as in the chameleon, whose eyes move
independently of each other. The clearness and length of vision will
depend, continues M. Müller, on the diameter of the sphere of which
the entire eye forms a segment, on the number and size of the
facettes, and the length of the cones or lenses. The larger each
facette, taken separately, and the more brilliant the pigment placed
between the lenses, the more distinct will be the image of objects at
a distance, and the less distinct that of objects near. With the
latter the luminous rays diverge considerably; while those from the
former are more parallel. In the first case, in traversing the
pigment, they impinge obliquely on the crystalline, and consequently
confuse the vision; in the second, they fall more perpendicularly on
each facette.
"Objects do not appear of the same size to each optic filament, unless
the eye is a perfect section of a sphere, and its convexity concentric
with that of the optic nerve. Whenever it is otherwise, the image
corresponds more or less imperfectly with the size of the object, and
is more or less incorrect. Hence it follows, that elliptical or
conical eyes, which one generally finds among insects, are less
perfect than those referred to above.
"The differences which exist in the organisation of the eye among
insects are explicable, to a certain point, on the theory which we are
about to explain in a few words. Those species which live in the same
substances on which they feed, and those which are parasitical, have
small and flattened eyes; those, on the contrary, which have to seek
their food, and which need to see objects at a distance, have large or
very convex eyes. For the same reason the males, which have to seek
their females, have larger eyes than the latter. The position of the
eyes depends also on their size and shape; those which are flat, and
have consequently a short field of vision, are placed close together,
and rather in front than at the sides of the head, and often
adjoining. Spherical and convex eyes, on the contrary, are placed on
the sides, and their axes are opposite. But the greater field of
vision which they are able to take in makes up for this position."
Almost all insects are provided with a pair of compound eyes, which
are placed on the sides of the head. The size and form of these organs
are very variable, as we shall presently see. They are generally
placed behind the antennæ.
Although simple eyes (ocelli or stemmata) are common, they do not
exist in all the orders of insects. They are generally round, and more
or less convex and black, and there are three in the majority of
cases. When there is this number they are most frequently placed in a
triangle behind, and at a greater or less distance from the antennæ.
Under the cornea, which varies in convexity, is found a transparent,
rather hard, and nearly globular body, which is the true crystalline
resting on a mass, which represents the vitreous body. This vitreous
body is enclosed in an expansion of the optic nerve. Besides these,
there is a pigment, most frequently red-brown, sometimes black, or
blood-red. The organisation of these eyes is analogous to the eyes of
fishes, and their refractive power is very great.
With these eyes insects can only see such objects as are at a short
distance. Of what use then can stemmata be to insects also provided
with compound eyes? It has been remarked that most insects having
this arrangement of eyes feed on the pollen of plants, and it has
been surmised that the stemmata enable them to distinguish the parts
of the flowers.
The antennæ, commonly called horns, are two flexible appendages,
of very variable form, which are joined to different parts of the
head, and are always two in number. The joints of which they are made
up have the power of motion, which enables the insect to move them in
any direction.
The antennæ consist of three parts: the basal joint, commonly
distinguished by its form, length, and colour; the club, formed by a
gradual or sudden thickening of the terminal joints, of which the
number, form, and size present great variations; lastly, the stalk,
formed by all the joints of the antennæ, except the basal, when no
club exists, and in case of the existence of a club, of all those
between it and the basal one.
We give as examples the antennæ of two beetles, one of the genus
_Asida_, the other of the genus _Zygia_ (Figs. 3 and 4).
[Illustration: Fig. 3.--Antenna of a species of Asida.]
[Illustration: Fig. 4.--Antenna of Zygia oblonga.]
Insects, for the most part, while in repose, place their antennæ on
their backs, or along the sides of the head, or even on the thorax.
Others are provided with cavities in which the antennæ repose either
wholly or in part.
During their different movements, insects move their antennæ more or
less, sometimes slowly and with regularity, at other times in all
directions. Some insects impart to their antennæ a perpetual
vibration. During flight they are directed in front, perpendicular to
the axis of the body, or else they repose on the back.
What is the use of the antennæ, resembling as they do, feathers, saws,
clubs, &c.? Everything indicates that these organs play a very
important part in the life of insects, but their functions are
imperfectly understood. Experience has shown that they only play a
subordinate part as feelers, and have nothing to do with the senses of
taste or smell. There is no other function for them to fulfil, except
that of hearing.
On this hypothesis the antennæ will be the principal instruments for
the transmission of sound-waves. The membrane at their base represents
a trace of the tympanum which exists among the higher animals. This
membrane then will have some connection with an auditory nerve.
The mouth of insects is formed after two general types, which
correspond to two kinds of requirements. It is suited in the one case
to break solid substances, in the other to imbibe liquids.
At first sight there seems no similarity between the mouth of a biting
insect and of one living by suction. But on examination it is found
that the parts of the mouth in the one are exactly analogous to the
same parts in the other, and that they have only modifications suiting
them to the different purposes which they have to fulfil.
The mouth of a biting insect is composed of an upper lip, a pair of
mandibles, a pair of jaws, and a lower lip (Fig. 5).
[Illustration: Fig. 5.--Mouth of a masticating insect.]
[Illustration: Fig. 6.--Thorax of Acrocinus longimanus (a beetle).]
The lower lip and the jaws carry on the outside certain appendages or
filaments which have received the name of _palpi_.
When speaking of sucking insects, and in general of the various orders
of insects, we shall speak more in detail of the various parts of the
mouth.
The thorax (Fig. 6), the second primary division of the body of
insects, plays almost as important a part as the head. It consists of
three segments or rings, which are in general joined together--the
prothorax, the mesothorax, and the metathorax, each of which bears a
pair of legs. The wings are attached to the two posterior segments.
All insects have six true legs. There is no exception whatever to this
rule, though some may not be developed.
From the segments to which they are attached, the legs are called
anterior, posterior, and intermediate. The legs are composed of four
parts: the trochanter, a short joint which unites the thigh to the
body; the thigh or _femur_; the _tibia_, answering to the shank in
animals; and the _tarsus_, or foot, composed of a variable number of
pieces placed end to end, and called the _phalanges_.
We take as examples the hind leg of a _Heterocerus_ (Fig. 7), and the
front leg of a _Zophosis_ (Fig. 8) (genera of beetles).
We shall not dwell on the different parts, as they perform functions
which will occupy us later, when speaking of the various species of
the great class of insects.
[Illustration: Fig. 7.--Hind leg of a Heterocerus.]
[Illustration: Fig. 8.--Front leg of a Zophosis.]
The functions which the legs of insects have to perform consist in
walking, swimming, or jumping.
In walking, says M. Lacordaire, insects move their legs in different
ways. Some move their six legs successively, or only two or three at
a time without distinction, but never both legs of the same pair
together, consequently one step is not the same as another. The walk
of insects is sometimes very irregular, especially when the legs are
long; and they often hop rather than walk. Others have one kind of
step, and walk very regularly. They commence by moving the posterior
and anterior legs on the same side and the intermediate ones on the
opposite side. The first step made, these legs are put down, and the
others raised in their turn to make a second.
Running does not change the order of the movements, it only makes them
quicker--very rapid in some species, and surpassing in proportion that
of all other animals; but in others the pace is slow. Some insects
rather crawl than walk.
[Illustration: Fig. 9.--Posterior leg of a jumping insect.]
In swimming, the posterior legs play the principal part. The other
legs striking the water upwards or downwards, produce an upward or
downward motion. The animal changes its course at will by using the
legs on one side only, in the same way as one turns a rowing boat with
one oar without the aid of a rudder. Swimming differs essentially from
walking, for the foot being surrounded by a resisting medium, the
legs on both sides are moved at the same time.
The act of jumping is principally performed by the hind legs. Insects
which jump have these legs very largely developed, as in Fig. 9. When
about to jump they bring the tibia into contact with the thigh, which
is often furnished with a groove to receive it, having on each side a
row of spines. The leg then suddenly straightens like a spring, and
the foot being placed firmly on the ground, sends the insect into the
air, and at the same time propels forward. The jump is greater in
proportion as the leg is longer.
To treat here in a general manner of the wings of insects would be
useless. We shall refer to them at length in their proper place, when
treating of the various types of winged insects.
In the perfect insect the abdomen does not carry either the wings or
the legs. It is formed of nine segments, which are without appendages,
with the exception of the posterior ones, which often carry small
organs differing much in form and function. These are saws, probes,
forceps, stings, augers, &c. We shall consider these different organs
in their proper places.
With vertebrate animals, which have an interior skeleton suited to
furnish points of resistance for their various movements, the skin is
a more or less soft covering, uniformly diffused over the exterior of
the body, and intended only to protect it against external injury. In
insects the points of resistance are changed from the interior to the
exterior. The skin is altered by Nature to fit it to this purpose. It
is hard, and presents between the segments only membranous intervals,
which allow the hard parts to move in all directions.
We are examining a perfect insect; we have glanced at its skeleton,
and the different appendages which spring from it. The principal
organs which are contained in the body remain to be examined.
We will first study the digestive apparatus. This apparatus consists
of a lengthened tubular organ, swollen at certain points, forming
more or less numerous convolutions, and provided with two distinct
orifices. This alimentary canal is always situated in the median line
of the body, traverses its whole length, and is at first surrounded
by, and then passes above, the nervous ganglia.[1]
[1] _Ganglion_--a mass, literally a knot, of nervous matter.
In its most complicated form the alimentary canal is composed of an
_oesophagus_, or gullet, of a crop, of a gizzard, of a chylific
ventricle or stomach, a small intestine, a large intestine, divers
appendages, salivary, biliary, and urinary glands. The oesophagus
is often not wider than a hair, and part of it in many species is
enlarged into a pouch, which is called the crop, because it occupies
the same position, and performs analogous functions with that organ in
birds. It is enough to say that the food remains there some time
before passing on to the other parts of the intestinal canal, and
undergoes a certain amount of preparation. It is in the gizzard, when
one exists, that the food, separated by the masticatory organs of the
mouth, undergoes another and more complete grinding. Its structure is
suited to its office. It is, in fact, very muscular, often half
cartilaginous, and strongly contractile. Its interior walls are
provided with a grinding apparatus, which varies according to the
species, and consists of teeth, plates, spines, and notches, which
convert the food into pulp. It only exists among insects which live
on solid matters, hard vegetables, small animals, tough skin, &c. This
apparatus is absent in sucking insects and those which live on soft
substances, such as the pollen of flowers, &c.
[Illustration: Fig. 10.--Digestive apparatus of Carabus auratus.]
The chylific ventricle or stomach is never absent; it is the organ
which performs the principal part in the act of digestion.
Two kinds of appendages belong to the chylific ventricle, but only in
certain families. The first are papillæ, in the form of the fingers of
a glove, which bristle over the exterior of this organ, and in which
it is believed that the food begins to be converted into chyle. The
second are cæca, and larger and less numerous.
They have been considered as secretory organs, answering to the
pancreas in vertebrate animals.
Fig. 10, which represents the digestive apparatus of _Carabus
auratus_, a common beetle, presents to the eyes of the reader the
different organs of which we are speaking.
A is the mouth of the insect, B the oesophagus, C the crop, D the
gizzard, E the chylific ventricle, F and G the small and large
intestines, and H the anus.
It is not necessary to consider the other parts of the alimentary
canal in insects, but only to refer to some of the appendages of this
apparatus.
The salivary glands pour into the digestive tube a liquid, generally
colourless, which, from the place where it is secreted, and its
alkaline nature, corresponds to the saliva in vertebrate animals. It
is this liquid which comes from the tongue of sucking insects in the
form of drops.
These glands are always two in number. Their form is as variable
as complicated. The most simple is that of a closed flexible tube,
generally rolled into a ball, and opening on the sides of the
oesophagus.
At the posterior extremity of the chylific ventricle are inserted
a variable number of fine tubes, usually elongated and flexible,
and terminating in _culs-de-sac_ at one end. Their colour, which
depends on the liquid they may contain, is sometimes white, but more
frequently brown, blackish, or green. They appear to be composed of a
very slight and delicate membrane, as they are very easily torn, and
nothing is more difficult than to unroll and to disengage them from
the fatty or other tissues by which they are enveloped.
[Illustration: Fig. 11.--Posterior extremity of the chylific
ventricle, surrounded by the Malpighian vessels.]
The function of these vessels is uncertain. Cuvier and Léon Dufour
supposed them to be analogous to the liver, and on that account they
have been called biliary vessels; and they are often termed the
Malpighian vessels, after the name of their discoverer.
According to M. Lacordaire, their functions vary with their position.
When they enter the chylific ventricle, they furnish only bile; bile
and a urinary liquid when they enter the posterior part of the
ventricle and the intestine; and urine alone when they are placed near
the posterior extremity of the alimentary canal.
Fig. 11 represents part of the preceding figure more highly magnified,
showing the manner in which these tubes enter the chylific ventricle.
In our rapid description of the digestive apparatus of insects, it
only remains for us to mention certain purifying organs which secrete
those fluids, generally blackish, caustic, or of peculiar smell, which
some insects emit when they are irritated, and which cause a smarting
when they get into one's eyes.
Less well developed than the salivary organs, they are often of a very
complicated structure. In Fig. 12 is represented the secretory
apparatus of the _Carabus auratus_, which will serve for an example: A
represents the secretory sacs aggregated together like a bunch of
grapes, B the canal, C the pouch which receives the secretion, D the
excretory duct.
[Illustration: Fig. 12.--Secretory apparatus of Carabus auratus.]
Sometimes the secretion is liquid, and has a foetid or ammoniacal
odour; sometimes, as in the Bombardier beetle (_Brachinus crepitans_),
it is gaseous, and is emitted, with an explosion, in the form of a
whitish vapour, having a strong pungent odour analogous to that of
nitric acid, and the same properties. It reddens litmus paper, and
burns and reddens the skin, which after a time becomes brown, and
continues so for a considerable time.
About the middle of the seventeenth century Malpighi at Bologna, and
Swammerdam at Utrecht, discovered a pulsatory organ occupying a median
line of the back, which appeared to them to be a heart, in different
insects. Nevertheless, Cuvier, having declared some time afterwards
that there was no circulation, properly so called, among insects, his
opinion was universally adopted.
But in 1827 a German naturalist named Carus discovered that there were
real currents of blood circulating throughout the body, and returning
to their point of departure. The observations of Carus were repeated
and confirmed by many other naturalists, and we are thus enabled to
form a sufficiently exact idea of the manner in which the blood
circulates.
The following summary of the phenomena of circulation among insects is
borrowed from "Leçons sur la Physiologie et l'Anatomie comparée," by
M. Milne-Edwards:--
The tube which passes under the skin of the back of the head, and
front part of the body, above the alimentary canal, has been known for
a long time as the dorsal vessel. It is composed of two very distinct
portions: the anterior, which is tubular and not contractile; and the
posterior, which is larger, of more complicated structure, and which
contracts and dilates at regular intervals.
This latter part constitutes, then, more particularly the heart of
the insect. Generally it occupies the whole length of the abdomen,
and is fixed to the vault of the tegumentary skeleton by membranous
expansions, in such a manner as to leave a free space around it, but
shut above and below, so as to form a reservoir into which the blood
pours before penetrating to the heart. This reservoir is often called
the auricle, for it seems to act as an instrument of impulsion, and to
drive the blood into the ventricle or heart, properly so called.
The heart is fusiform, and is divided by numerous constrictions into
chambers. These chambers have exits placed in pairs, and membranous
folds which divide the cavity in the manner of a portcullis. The lips
of the orifices, instead of terminating in a clean edge, penetrate
into the interior of the heart in the form of the mouth-piece of a
flute. The double membranous folds thus formed on each side of the
dorsal vessel are in the shape of a half moon, and separate from each
other when this organ dilates; but the contrary movement taking place,
the passage is closed.
By the aid of this valvular apparatus, the blood can penetrate into
the heart from the pericardic chamber, the empty space surrounding the
heart, but cannot flow back from the heart into that reservoir.
The anterior or aortic portion of the dorsal vessels shows neither
fan-shaped lateral expansions, nor orifices, and consists of a
single membranous tube. The whole of the blood set in motion by the
contractions of the cardial portion of the dorsal vessel runs into the
cavity of the head, and circulates afterwards in irregular channels
formed by the empty spaces left between the different organs. It is
the unoccupied portions of the great visceral cavity which serve as
channels for the blood, and through them run the main currents to the
lateral and lower parts of the body. These currents regain the back
part of the abdomen, and enter the heart after having passed over the
internal organs. These principal channels are in continuity with other
gaps between the muscles, or between the bundles of fibres of which
these muscles are composed.
The principal currents send into the network thus formed, minor
branches, which having ramified in their turn among the principal
parts of the organism, re-enter some main current to regain the dorsal
vessel.
In the transparent parts of the body the blood may be seen circulating
in this way to a number of inter-organic channels, penetrating
the limbs and the wings, when these appendages are not horny, and,
in short, diffusing itself everywhere. "If, by means of coloured
injections," says M. Milne-Edwards, "one studies the connections which
exist between the cavities in which sanguineous currents have been
found to exist and the rest of the economy, it is easy to see that the
irrigatory system thus formed penetrates to the full depth of every
organ, and should cause the rapid renewal of the nourishing fluid in
all the parts where the process of vitality renders the passage of
this fluid necessary."
We shall see presently, in speaking of respiration, that the relations
between the nourishing fluid and the atmospheric air are more direct
and regular than was for a long time supposed.
In short, insects possess an active circulation, although we find
neither arteries nor veins, and although the blood put in motion by
the contractions of the heart, and carried to the head by the aortic
portion of the dorsal vessel, can only distribute itself in the
different parts of the system to return to the heart, by the gaps left
between the different organs, or between the membranes and fibres of
which these organs are composed.
Fig. 13 (page 14), which shows both the circulating and breathing
systems of an insect, enables us to recognise the different organs
which we have described, as helping to keep up both respiration and
circulation.
The knowledge of the respiration of the insect is comparatively a
modern scientific acquisition. Malpighi was the first to prove, in
1669, that insects are provided with organs of respiration, and that
air is as indispensable to them as it is to other living beings. But
the opinion of this celebrated naturalist has been contradicted,
and his views were long contested. Now, however, one can easily
recognise the apparatus by the aid of which the respiration of the
insect is effected.
[Illustration: Fig. 13.--Organs of circulation and breathing in an
insect. A, abdominal portion of the dorsal vessel. B, aortic or
thoracic portion. C, air-vessels of the head; D, of the abdomen.]
The respiratory apparatus is essentially composed of membranous
ducts of great tenuity, their ramifications spread everywhere in
incalculable numbers, and bury themselves in the different organs,
much in the same way as the fibrous roots of plants bury themselves in
the soil. These vessels are called tracheæ. Their communications with
the air are established externally in different ways, according to the
character of the medium in which the insect lives.
It is well known that a vast number of insects live in the air. The
air penetrates into the tracheæ by a number of orifices placed at the
sides of the body, which are termed spiracles. On close examination
these may be seen in the shape of button-holes in a number of
different species. Let us dwell for a moment on the breathing
apparatus of the insect, that is to say, on the tracheæ.
This apparatus is sometimes composed of elastic tubes only, sometimes
of a collection of tubes and membranous pouches. We will first treat
of the former.
The coats of these breathing tubes are very elastic, and always
preserve a cylindrical form, even when not distended. This state of
things is maintained by the existence, throughout the whole length of
the tracheæ, of a thread of half horny consistency, rolled up in a
spiral, and covered externally by a very delicate membranous sheath.
The external membrane is thin, smooth, and generally colourless, or of
a pearly white. The cartilaginous spiral is sometimes cylindrical and
sometimes flat. It only adheres slightly to the external membrane,
but is, on the other hand, closely united to the internal one. This
spiral thread is only continuous in the same trunk; it breaks off when
it branches, and each branch then possesses its own thread, in such a
way that it is not joined to the thread of the trunk from which it
issued, except by continuity, just as the branch of a tree is attached
to the stem which supports it. This thread is prolonged, without
interruption, to the extreme points of the finest ramifications.
The number of tracheæ in the body of an insect is very great. That
patient anatomist, Lyonet, has proved this in his great work on the
Goat-moth Caterpillar, _Cossus ligniperda_. Lyonet, who congratulated
himself with having finished his long labours without having had to
destroy more than eight or nine of the species he wished to describe,
had the patience to count the different air-tubes in that caterpillar.
He found that there were 256 longitudinal and 1,336 transverse
branches; in short, that the body of this creature is traversed in all
directions by 1,572 aeriferous tubes which are visible to the eye by
the aid of a magnifying glass, without taking into account those which
may be imperceptible.
The complicated system of the breathing apparatus which we are
describing is sometimes composed of an assemblage of tubes and
membranous pouches, besides the elastic tubes which we have already
mentioned. These pouches vary in size, and are very elastic, expanding
when the air enters, and contracting when it leaves them, as they are
altogether without the species of framework formed by the spiral
thread of the tubular tracheæ, of which they are only enlargements.
Fig. 13 is explanatory of these organs of respiration.
The respiratory mechanism of an insect is easily understood. "The
abdominal cavity," says M. Milne-Edwards, "in which is placed the
greater part of the respiratory apparatus, is susceptible of being
contracted and dilated alternately by the play of the different
segments of which the skeleton is composed, and which are placed in
such a manner that they can be drawn into each other to a greater or
less extent. When the insect contracts its body, the tracheæ are
compressed and the air driven out. But when, on the other hand, the
visceral cavity assumes its normal size, or dilates, these channels
become larger, and the air with which they are filled being rarefied
by this expansion, is no longer in equilibrium with the outer air with
which it is in communication through the medium of the spiracles. The
exterior air is then impelled into the interior of the respiratory
tubes, and the inspiration is effected."
The respiratory movements can be accelerated or diminished, according
to the wants of the animal; in general, there are from thirty to fifty
to the minute. In a state of repose the spiracles are open, and all
the tracheæ are free to receive air whenever the visceral cavity is
dilated, but those orifices may be closed, and the insect thus
possesses the faculty of stopping all communication between the
respiratory apparatus and the surrounding atmosphere.
Some insects live in the water; they are therefore obliged to come to
the surface to take the air they are in need of, or else to possess
themselves of the small amount contained in the water. Both these
methods of respiration exist under different forms in aquatic insects.
To inhale atmospheric air, which is necessary for respiration, above
the water, certain insects employ their elytra[2] as a sort of
reservoir; others make use of their antennæ, the hairs of which retain
the globules of air. In this case it is brought under the thorax,
whence a groove carries it to the spiracles. Sometimes the same result
is obtained by a more complicated arrangement, consisting of
respiratory tubes which can be thrust into the air, which it is their
function to introduce into the organisation.
[2] The horny upper wings with which some insects are provided
are called elytra.--ED.
Insects which breathe in the water without rising to the surface are
provided with gills--organs which, though variable in form, generally
consist of foliaceous or fringed expansions, in the midst of which the
tracheæ ramify in considerable numbers. These vessels are filled with
air, but it does not disseminate itself in them directly, and it is
only through the walls of these tubes that the contained gas is
exchanged for the air held in suspension by the surrounding water. The
oxygen contained in the water passes through certain very permeable
membranes of the gill, and penetrates the tracheæ, which discharge, in
exchange, carbonic acid, which is the gaseous product of respiration.
[Illustration: Fig. 14.--Branchiæ, or gills, of an aquatic larva
(_Ephemera_). A, foliaceous laminæ, or gills.]
Fig. 14 represents the gills or breathing apparatus in an aquatic
insect. We take as an example _Ephemera_.[3] It may be observed that
the gills or foliaceous laminæ are placed at the circumference of the
body, and at its smallest parts.
[3] May-fly family.--ED.
We have now seen that the respiratory apparatus is considerably
developed in insects; it is, therefore, easy to foresee that those
functions are most actively employed by them. In fact, if one
compares the oxygen they imbibe with the heavy organic matter of which
their body is composed, the amount is enormous.
Before finishing this rapid examination of the body of an insect, we
shall have to say a few words on the nervous system.
This system is chiefly composed of a double series of ganglions, or
collections of nerves, which are united together by longitudinal
cords. The number of these ganglions corresponds with that of the
segments. Sometimes they are at equal distances, and extend in a chain
from one end of the body to the other; at others they are many of them
close together, so as to form a single mass.
The cephalic ganglions are two in number; they have been described by
anatomists under the name of brain. "This expression," says M.
Lacordaire, "would be apt to mislead the reader, as it would induce
him to suppose the existence of a concentration of faculties to
control the feelings and excite the movements, which is not the
case."[4] The same naturalist observes, "All the ganglions of the
ventral chain are endowed with nearly the same properties, and
represent each other uniformly."
[4] "Introduction à l'Entomologie," tome ii. p. 192. 8vo.
Paris. 1838.
The ganglion situated above the oesophagus gives rise to the optic
nerves, which are the most considerable of all those of the body, and
to the nerves of the antennæ. The ganglion beneath the oesophagus
provides the nerves of the mandibles, of the jaws, and of the lower
lip. The three pairs of ganglions which follow those placed
immediately below the oesophagus, belong to the three segments of
the thorax, and give rise to the nerves of the feet and wings. They
are in general more voluminous than the following pairs, which occupy
the abdomen.
Fig. 15 represents the nervous system of the _Carabus auratus_: A is
the cephalic ganglion; B, the sub-oesophagian ganglion; C, the
prothoracic ganglion; D and E are the ganglions of the mesothorax and
metathorax. The remainder, F F, are the abdominal ganglions.
Before finishing these preliminary observations, it is necessary to
say that the preceding remarks only apply absolutely to insects
arrived at the perfect state. It is important to make this remark, as
insects, before arriving at that state, pass through various other
stages. These stages are often so different from each other, that it
would be difficult to imagine that they are only modifications of the
same animal; one would suppose that they were as many different kinds
of animals, if there was not abundant proof of the contrary.
[Illustration: Fig. 15.--Nervous system of Carabus auratus.]
The successive stages through which an insect passes are four in
number:--the egg; the larva; the pupa, nymph, or chrysalis; and the
perfect insect, or imago.
The egg state, which is common to them, as to all other articulate
animals, it is unnecessary to explain. Nearly all insects lay eggs,
though some few are viviparous. There often exists in the extremity of
the abdomen of the female a peculiar organ, called the ovipositor,
which is destined to make holes for the reception of the eggs. By a
wonderful instinct the mother always lays her eggs in a place where
her young, on being hatched, can find an abundance of nutritious
substances. It will not be needless to observe that in most cases,
these aliments are quite different to those which the mother seeks for
herself.
In the second stage, that is to say, on leaving the egg--the larva
period--the insect presents itself in a soft state, without wings, and
resembles a worm. In ordinary language, it is nearly always called a
worm, or grub, and in certain cases, a caterpillar.
Linnæus was the first to use the term "larva"--taken from the Latin
word _larva_, "a mask"--as he considered that, in this form, the
insect was as it were masked. During this period of its life the
insect eats voraciously, and often changes its skin. At a certain
period it ceases to eat, retires to some hidden spot, and, after
changing its skin for the last time, enters the third stage of its
existence, and becomes a chrysalis. In this state it resembles a mummy
enveloped in bandages, or a child in its swaddling clothes. It is
generally incapable of either moving or nourishing itself. It
continues so for days, weeks, months, and sometimes even for years.
While the insect is thus apparently dead, a slow but certain change is
going on in the interior of its body. A marvellous work, though not
visible outside, is being effected, for the different organs of the
insect are developing by degrees under the covering which surrounds
them. When their formation is complete, the insect disengages itself
from the narrow prison in which it was enclosed, and makes its
appearance, provided with wings, and capable of propagating its kind;
in short, of enjoying all the faculties which Nature has accorded to
its species. It has thrown off the mask; the larva and pupa has
disappeared, and given place to the perfect insect.
To show the reader the four states through which the insect passes in
succession, in Fig. 16 is represented the insect known as the
_Hydrophilus_,[5] firstly, in the egg state; secondly, as the larva,
or caterpillar; thirdly in the pupa; and fourthly as the perfect
insect or imago. The different degrees of transformation and evolution
which we have just described, are those which take place either
completely or incompletely in all insects. Their metamorphoses are
then at an end. There are certain insects, however, that show no
difference in their various stages, except by absence of wings in
the larva; and in these the chrysalis is only characterised by the
growth of the wings, which, at first folded back and hidden under
the skin, afterwards become free, but are not wholly developed till
the last skin is cast. These insects are said to undergo incomplete
metamorphoses, the former complete metamorphoses. Some never possess
wings; indeed, there are others which undergo no metamorphosis, and
are born possessed of all the organs with which it is necessary they
should be provided.
[5] A kind of water-beetle.--ED.
[Illustration: Fig. 16.--Hydrophilus in its four states. A, eggs; B,
larva; C, pupa; D, imago, or perfect insect.]
Some curious researches have been lately made on the strength
of insects. M. Felix Plateau, of Brussels, has published some
observations on this point, which we think of sufficient interest to
reproduce here.
In order to measure the muscular strength of man, or of animals--as
the horse, for instance--many different dynamometric apparatuses have
been invented, composed of springs, or systems of unequal levers. The
Turks' heads which are seen at fairs, or in the Champs Élysées, at
Paris, and on which the person who wishes to try his strength gives a
strong blow with his fist, represent a dynamometer of this kind. The
one which Buffon had constructed by Régnier the mechanician, and which
is known by the name of Régnier's Dynamometer, is much more precise.
It consists of an oval spring, of which the two ends approach each
other; when they are pulled in opposite directions, a needle, which
works on a dial marked with figures, indicates the force exercised on
the spring. It has been proved, with this instrument, that the
muscular effort of a man pulling with both hands is about 124 lbs.,
and that of a woman only 74 lbs. The ordinary effort of strength of a
man in lifting a weight is 292 lbs.; and a horse, in pulling, shows a
strength of 675 lbs.; a man, under the same circumstances, exhibiting
a strength of 90 lbs.
Physiologists have not as yet given their attention to the strength of
invertebrate animals. It is, relatively speaking, immense. Many people
have observed how out of proportion a jump of a flea is to its size. A
flea is not more than an eighth of an inch in length, and it jumps a
yard; in proportion, a lion ought to jump two-thirds of a mile. Pliny
shows, in his "Natural History," that the weights carried by ants
appear exceedingly great when they are compared with the size of these
indefatigable labourers. The strength of these insects is still more
striking, when one considers the edifices they are able to construct,
and the devastations they occasion. The _Termes_, or White Ant,[6]
constructs habitations many yards in height, which are so firmly and
solidly built, that the buffaloes are able to mount them, and use them
as observatories; they are made of particles of wood joined together
by a gummy substance, and are able to resist even the force of a
hurricane.
[6] A neuropterous insect, not a true ant.--ED.
There is another circumstance which is worth being noted. Man is proud
of his works; but what are they, after all, in comparison with those
of the ant, taking the relative heights into consideration? The
largest pyramid in Egypt is only 146 yards high, that is, about ninety
times the average height of man; whereas, the nests of the Termites
are a thousand times the height of the insects which construct them.
Their habitations are thus twelve times higher than the largest
specimen of architecture raised by human hands. We are, therefore,
far beneath these little insects, as far as strength and the spirit
of working go.
The destructive power of these creatures, so insignificant in
appearance, are still more surprising. During the spring of a single
year they can effect the ruin of a house by destroying the beams and
planks. The town of La Rochelle, to which the Termites were imported
by an American ship, is menaced with being eventually suspended on
catacombs, like the town of Valencia in New Grenada. It is well known
what destruction is caused when a swarm of locusts alight in a
cultivated field; and it is certain that even their larvæ do as severe
injury as the perfect insect. All this sufficiently proves the
destructive capabilities of these little animals, which we are
accustomed to despise.
M. Plateau has studied the power of traction in some insects, the
power of pushing in the digging insects, and the lifting power of
others during flight. He has thus been able to make some most
interesting comparisons, of some of which we will relate the results.
The average weight of man being 142 lbs., and his power of traction,
according to Régnier, being 124 lbs., the proportion of the weight he
can draw to the weight of his body is only as 87 to 100. With the
horse the proportion is not more than 67 to 100, a horse 1,350 lbs. in
weight only drawing about 900 lbs. The horse, therefore, can draw
little more than half his own weight, and a man cannot draw the weight
of his own body.
This is a very poor result, if compared with the strength of the
cockchafer. This insect, in fact, possesses a power of traction equal
to more than fourteen times its own weight. If you amuse yourself with
the children's game of making a cockchafer draw small cargoes of
stones, you will be surprised at the great weight which this
insignificant looking animal is able to manage.
To test the power of traction in insects, M. Plateau attached them to
a weight by means of a thread fastened to one of their feet. The
_Coleoptera_ (Beetles) are the best adapted for these experiments.
The following are some of the results obtained by the Belgian
physician:--_Carabus auratus_ can draw seven times the weight of its
body; _Nebria brevicollis_, twenty-five times; _Necrophorus vespillo_,
fifteen times; _Trichius fasciatus_, forty-one times; and _Oryctes
nasicornis_, four times only. The bee can draw twenty times the weight
of its body; _Donacia nymphæ_[7] forty-two times its own weight.
[7] A beetle.--ED.
From this it follows that if the horse possessed the same strength as
this last insect, or if the insect were the size of a horse, they
would either of them be able to draw 155,250 lbs. M. Plateau has
ascertained the pushing power in insects, by introducing them into a
pasteboard tube, the interior of which was made rough, and in which
was fixed a glass plate, which allowed the light to penetrate into the
prison. The animal, if excited, struggled with all its strength
against the transparent plate, which, on being pushed forward, turned
a lever adapted to a miniature dynamometer, which indicated the amount
of effort exercised.
The results thus obtained prove that the pushing power, like the power
of traction, is greater in inverse proportion to the size and weight
of the animal. A few figures will better explain this curious law. In
_Oryctes nasicornis_ the proportion of the pushing power to the weight
of the insect is only three to two; in _Geotrupes stercorarius_ it is
sixteen to two; and in _Onthophagus nuchicornis_ seventy-nine to six.
Experiments have been made on the lifting power of insects by
fastening a ball of soft wax to a thread attached to the hind legs.
The proportion of the weight lifted has been found equal to that of
the body. That is to say, that the insect, when flying, can lift its
own weight. This is proved by the following calculations:--In the
Neuroptera the proportion is 1 in the Dragon-fly (_Libellula
vulgata_), ·7 in _Lestes sponsa_. In the order Hymenoptera it is ·78
in the bee, and ·63 in _Bombus terrestris_, the humble-bee. In the
Diptera it is ·9 in _Calliphora vomitoria_,[8] 1·84 in the _Syrphus
corollæ_, and 1·77 in the house-fly.
[8] The meat-fly.--ED.
These results show that insects have only sufficient power to sustain
their own weight when flying, as the above calculations exhibit the
maximum of which they are capable, and at the utmost this strength
would only compensate for the fatigue occasioned by the action of
flight.
At the same time it is to be observed that the Diptera, and among
others the house-fly, can sustain their flight longer than the
Hymenoptera and Neuroptera, although one would not think so from their
appearance. In conclusion, if an insect's power of flying is not
considerable, its power of traction and propulsion are immense,
compared with the vertebrate animals; and, in the same group of
insects, those that are the smallest and lightest are the strongest.
The proportion between the muscular strength of insects and the
dimensions of their bodies, would not appear to be on account of
their muscles being more numerous than those of vertebrate animals,
but on account of greater intrinsic energy and muscular activity. The
articulations of insects may be considered as solid cases which
envelop the muscles, and the thickness of these cases appears to
decrease in a singular manner according to the size of the creature.
The relative bulk of the muscles being less in the smaller species
than in the larger, it is necessary to explain the superior relative
strength of the former by supposing them to possess a greater amount
of vital energy.
These astonishing phenomena will perhaps be better understood if we
consider the obstacles which insects have to overcome to satisfy their
wants, to seek their food, to defend themselves against their enemies,
&c.
To meet these requirements they are marvellously constructed for both
labour and warfare, and their strength is superior to that displayed
by all other animals. It is also much greater than that of the
machines we construct to replace manual labour. They represent
strength itself. God's workmen are infinitely more powerful than those
invented by the genius of man, which we call machines.
We think it necessary, in closing this chapter, to give a sort of
general outline of the great class of animals which we are about to
study. If we wished to characterise insects by their exterior aspect,
we might consider them as articulate animals, whose bodies, covered
with tough and membranous integuments, are divided into three distinct
parts: the head, provided with two antennæ, and eyes and mouth of very
variable form; a trunk or thorax, composed of three segments, which
has underneath it always six articulated limbs, and often above it two
or four wings; and an abdomen, composed of nine segments, although
some may not appear to exist at first sight.
If, in addition to these characteristics, one considers that these
animals are not provided with interior skeletons--that their nervous
system is formed of a double cord, swelling at intervals, and placed
along the under-side of the body, with the exception of the first
swellings or ganglions which are under the head--that they are not
provided with a complete circulating system--that they breathe by
particular organs, termed tracheæ, extending parallel to each other
along each side of the body, and communicating with the exterior
air by lateral openings termed spiracles--that their sexes are
distinct--that they are reproduced from eggs--and, in conclusion,
that the different parts we have mentioned are not complete until
the creature has passed through several successive changes, called
metamorphoses, a general idea may be formed of what is meant in
zoology by the word "insect."
Insects, whose general organisation we have briefly traced, have been
classed by naturalists as follows:--
1. APTERA (Fleas and Lice).
2. DIPTERA (Gnats, Flies, &c.)
3. HEMIPTERA (Bugs, &c.)
4. LEPIDOPTERA (Butterflies and Moths).
5. ORTHOPTERA (Grasshoppers, Crickets, Cockroaches, &c.)
6. HYMENOPTERA (Bees, Wasps, &c.)
7. THYSANOPTERA (_Thrips cerealium_).
8. NEUROPTERA (_Libellula_, or Dragon-fly; _Ephemera_,
or May-fly; _Phryganea_, or Alder-fly).
9. COLEOPTERA (Beetles).
We shall commence the history of the various orders by examining the
Aptera.
I.
APTERA.
Insects of this order are without wings, and the name is derived from
two Greek words, [Greek: a], privative, and [Greek: pteron], wing,
indicating the negative character which constitutes this order.[9] It
consists of Fleas and Lice. The Flea (_Pulex_), of which De Geer
formed a separate group, and called _Suctoria_, includes several
species.
[9] It is probable that one day the order Aptera will be
superseded. The absence of wings is not really a character of
great value. De Blainville, Mollard, Pouchet, Van Beneden, and
Gervais, have made several attempts in that direction. The
fleas have been placed among the Diptera, and the lice among
Hemiptera in the "Traité de Zoologie Médicale" of these two
last authors.
The common flea (_Pulex irritans_, Fig. 17) has a body of oval form,
somewhat flattened, covered with a rather hard horny skin of a
brilliant chestnut brown colour. It is the breaking of this hard skin
which produces the little crack which is heard when, after a
successful hunt, one has the happiness to crush one of these parasites
between one's nails.
[Illustration: Fig. 17.--Flea (_Pulex irritans_).]
Its head, small in proportion to the body, is compressed, and carries
two small antennæ, of cylindrical form, composed of four joints, which
the animal shakes continually when in motion, but which it lowers and
rests in front of its head when in a state of repose. The eyes are
simple, large, and round. The beak is composed of an exterior jointed
sheath, having inside it a tube, and carrying underneath two long
sharp lancets, with cutting and saw-like edges. It is with this
instrument that the flea pierces the skin, irritates it, and causes
the blood on which it lives to flow.
This bite, as every one knows, is easily recognised by the presence of
small darkish red spots, surrounded by a circle of a paler colour.
The quantity of blood absorbed by this little creature is enormous,
when compared with its size.
The body of the flea is divided into thirteen segments, of which one
forms the head; three the thorax, which is short, and the remainder
the abdomen.
The limbs are long, strong, and spiny. The tarsus, or foot, has five
joints, and terminates in hooks turned in opposite directions. The two
anterior limbs are separated from the others, and are inserted nearly
under the head; the posterior ones are particularly large and strong.
The jumps which fleas are able to make are really gigantic, and the
strength of these little animals quite herculean, when compared with
the size of their bodies. The reader may be inclined to smile at the
assertion that the flea possesses herculean strength; but let him wait
a little, and he will find that it is no exaggeration.
To give some idea of the strength, the docility, and the goodwill of
the fleas, some wonderful little things have been made, which have
served at the same time to show the astonishing skill of certain
workmen.
In his "Histoire abrégée des Insectes," published in the seventh year
of the French Republic, Geoffroy relates that a certain Mark, an
Englishman, had succeeded, by dint of patience and art, in making a
gold chain the length of a finger, with a padlock and a key to fasten
it, not exceeding a single grain in weight. A flea attached to the
chain pulled it easily. The same learned writer relates a still more
surprising fact. An English workman constructed a carriage and six
horses of ivory. The coachman was on the box, with a dog between his
legs, there were also a postillion, four persons in the carriage, and
two servants behind, and the whole of this was drawn by one flea.
In his "Histoire Naturelle des Insectes Aptères," Baron Walckenaer
relates the following marvellous instance of industry, patience, and
dexterity:--
"I think it is about fifteen years ago, that the whole population of
Paris could see the following wonders exhibited on the Place de la
Bourse for sixty centimes. They were the learned fleas. I have seen
and examined them with entomological eyes, assisted by a glass.
"Thirty fleas went through military exercise, and stood upon their
hind legs, armed with pikes, formed of very small splinters of wood.
"Two fleas were harnessed to and drew a golden carriage with four
wheels and a postillion. A third flea was seated on the coach-box, and
held a splinter of wood for a whip. Two other fleas drew a cannon on
its carriage; this little trinket was admirably finished, not a screw
or a nut was wanting. These and other wonders were performed on
polished glass. The flea-horses were fastened by a gold chain attached
to the thighs of their hind legs, which I was told was never taken
off. They had lived thus for two years and a half, not one having died
during the period. To be fed, they were placed on a man's arm, which
they sucked. When they were unwilling to draw the cannon or the
carriage, the man took a burning coal, and on it being moved about
near them, they were at once roused, and recommenced the
performances."
The learned fleas were the admiration and amazement of Paris, Lyons,
and the chief provincial towns of France, in 1825.
But how, one will ask, was it possible in a large public room to see
this wonderful sight? And it is necessary that this should be
explained. The spectators were seated in front of a curtain, provided
with magnifying glasses, through which they looked, as they would at a
diorama of landscapes or buildings.
But let us return to the natural history of our insect. The female
flea lays from eight to twelve eggs, which are of oval shape, smooth,
viscous, and white.
Contrary to what one might think, _à priori_, the flea does not fix
its eggs to the skin of its victims. She lets them drop on the ground,
between the boards of floors, or old furniture, and among dirty linen
and rubbish.
M. Defrance has remarked that there are always found mixed with the
eggs a certain number of grains of a brilliant black colour, which are
simply dried blood. This is a provision which the foreseeing mother
has prepared at our expense to nourish her young offspring.
In four or five days in summer, and in eleven days in winter, one may
see coming out of these eggs small, elongated larvæ, of cylindrical
form, covered with hair, and divided into three parts, the last
provided with two small hooks. The head is scaly above, has two small
antennæ, and is without eyes. These larvæ are without limbs, but they
can twist about, roll themselves over and over, and even advance
pretty fast by raising their heads. Though at first white, they become
afterwards of a reddish colour.
About a fortnight after they are hatched they cease to eat, and are
immovable, as if about to die. They then commence to make a small,
whitish, silky cocoon, in which they are transformed into pupæ. In
another fortnight these pupæ become perfect insects.
A most remarkable trait, and unique among insects, has been observed
in the flea. The mother disgorges into the mouths of the larvæ the
blood with which she is filled.
The flea is most abundant in Europe and the North of Africa. Certain
circumstances particularly favour its multiplication; being most
abundant in dirty houses, in barracks, and in camps; in deserted
buildings, in ruins, and in places frequented by people of uncleanly
habits.
Other kinds of fleas live on animals, as, for example, the cat flea,
the dog flea, and those of the pigeon and poultry.
We shall say a few words about a peculiar species which abounds in all
the hot parts of America, but principally in the Brazils and the
neighbouring countries. This formidable species is the Chigo (_Pulex
penetrans_).
The chigo, called also the tick, is smaller than the common flea. It
is flat, brown with a white spot on the back, and is armed with a
strong pointed stiff beak, provided with three lancets. It is with
this instrument that the female attacks man with the intention of
lodging in his skin and bringing forth her young there.
The chigo attacks chiefly the feet. It slips in between the flesh and
the nails, or gets under the skin of the heel. Notwithstanding the
length of the animal's beak, introducing itself beneath the skin does
not at first cause any pain; but after a few days one is made aware of
its presence by an itching, which, though at first slight, gradually
increases, and ends by becoming unbearable.
The chigo, when under the skin, betrays itself by a bump outside. Its
body has now become as large as a pea; in the attacked skin a large
brown bag containing matter is formed. In this bag are collected the
eggs, which issue from an orifice in the posterior extremity, and are
not hatched in the wound itself, as was long thought to be the case.
The chigoes are an object of terror to the Brazilian negroes. These
formidable parasites sometimes attack the whole of the foot, which
they devour, and thus bring on mortification; many negroes losing the
bones of some of their toes by the ravages of these dangerous
creatures. To guard against their attacks, they wear thick shoes, and
examine their feet carefully every day. The plan usually followed in
the Brazils to prevent the chigoes from injuring the feet, is to
employ children, who, by their sharpness of sight, can easily perceive
the red spot on the skin where the chigo has entered. These children
are in the habit of extracting the insect from the wound by means of a
needle. But this is not without risk; as, if any portion of the insect
remains in the wound, a dangerous inflammation may ensue. For this
reason, operators who are renowned for their skill are much sought
after, flattered, and rewarded by the poor negroes of the plantations.
[Illustration: Fig. 18.--Louse (_Pediculus capitis_) magnified.]
The Head Louse (_Pediculus capitis_, Fig. 18) is an insect with a flat
body, slightly transparent, and of greyish colour, spotted with black
on the spiracles, soft in the middle, and rather hard at the sides.
The head, which is oval, is furnished with two thread-like antennæ,
composed of five joints, which are constantly in motion while the
creature is walking; it is also furnished with two simple, round,
black eyes; and lastly, with a mouth. In the front of the head is a
short, conical, fleshy nipple. This nipple contains a sucker, or
rostrum, which the animal can put out when it likes, and which, when
extended, represents a tubular body, terminating in six little pointed
hooks, bent back, and serving to retain the instrument in the skin.
This organ is surmounted by four fine hairs, fixed to one another, and
seated in its interior. It is by means of this complicated apparatus
that the louse pricks and sucks the skin of the head. The thorax is
nearly square, and divided into three parts by deep incisions. The
abdomen, strongly lobed at the sides, is composed of eight rings, and
is provided with sixteen spiracles. The limbs consist of a trochanter,
a thigh, a shank, and a tarsus of a single joint, and are very thick.
A strong nail, which folds back on an indented projection, thus
forming a pincer, terminates the tarsus. It is with this pincer that
the louse fastens itself to the hair.
Lice are oviparous. Their eggs, which remain sticking to the hair, are
long and white, and are commonly called "nits." The young are hatched
in the course of five or six days; and in eighteen days are able to
reproduce their kind. Leuwenhoek calculated that in two months two
female lice could produce ten thousand! Other naturalists have
asserted that the second generation of a single individual can amount
to two thousand five hundred, and the third, to a hundred and
twenty-five thousand! Happily for the victims of these disgusting
parasites, their reproduction is not generally to this prodigious
extent.
Many means are employed to kill lice. Lotions of the smaller centaury
or of stavesacre, and pomatum mixed with mercurial ointment, are very
efficacious. But the surest and easiest remedy is to put plenty of oil
on the head. The oil kills the lice by obstructing their tracheæ, and
thus stopping respiration.
There are other kinds of lice, but we will only mention the louse
which infests beggars and people of unclean habits, _Pediculus humanus
corporis_, producing the complaint called phthiriasis. In the victims
of this disease these parasites increase with fearful rapidity. This
dreadful disorder is often mentioned by the ancients. King Antiochus,
the philosopher Pherecydes of Scyros, the contemporary and friend of
Thales, the dictator Sylla, Agrippa, and Valerius Maximus, are said to
have been attacked by phthiriasis, and even to have died of it. Amatus
Lusitanus, a Portuguese doctor of the sixteenth century, relates that
lice increased so quickly and to such an extent on a rich nobleman
attacked with phthiriasis, that the whole duty of two of his servants
consisted in carrying away, and throwing into the sea, whole
basketfuls of the vermin, which were continually escaping from the
person of their noble master.
Little is known at the present day of the details of this complaint,
though it is observed frequently enough in some parts of the south of
Europe, where the dirty and miserable inhabitants are a prey to
poverty and uncleanliness--two misfortunes which often go together. In
Gallicia, in Poland, in the Asturias, and in Spain, we may find many
victims of phthiriasis.
Lice increase with such rapidity on persons thus attacked, that it is
common to attribute their appearance to spontaneous generation alone.
But the prodigious rapidity of reproduction in these insects
sufficiently explains their increase, especially when it is admitted
that it is possible for the female louse to reproduce young without
the agency of the male.
The Thysanura or "Skip Tail" tribe are small insects, which are better
known on account of the beauty of their microscopic body scales than
for any interesting habits or instincts. They do not undergo
metamorphosis.
The Fish Scale or _Lepisma saccharina_, and the Skip Tail or _Podura
plumbea_ belong to the Thysanura.
II.
DIPTERA.
All suctorial insects which in the perfect state possess only two
membranous wings, are called Diptera, from two Greek words--[Greek:
dis], twice, and [Greek: pteron], wing.
The Diptera were known and scientifically described at a very early
date. They are frequently mentioned by Aristotle in his "History of
Animals;" and he applied the term to the same insects as now
constitute the order.
The absence of the second wings, common to other insects, which are in
this case replaced by two appendages, which have received the name of
balancers,[10] because they serve to regulate the action of flight,
constitutes the chief characteristic of the Diptera. Let us, however,
give a glance at their other organs, which have more or less affinity
with those which exist in other classes of insects, preserving,
nevertheless, their own especial characteristics.
[10] Sometimes called _halteres_.--ED.
The mouth, for instance--suited for suction only--is in the form of a
trunk, and is composed of a sheath, a sucker, and two palpi. The
antennæ are generally composed of only three joints. The eyes--usually
two in number--are very large, and sometimes take up nearly the whole
of the head. They are both simple and compound. The wings are
membranous, delicate, and veined; the limbs long and slight. In giving
the history of the principal types of Diptera, we shall explain more
fully the formation of these organs.
The Diptera, by their rapid flight, enliven both the earth and the
air. The different species abound in every climate, and in every
situation, some inhabiting woods, plains, fields, or banks of rivers;
others preferring our houses. They like the neighbourhood of
vegetation, choosing either the flowers, the leaves, or the stems of
the trees of our woods, our gardens, or our plantations. Their food
varies very much; and the formation of the sucker is regulated by it.
Some imbibe blood, others live on the secretions of animals. Their
chief nourishment, however, consists of the juices of flowers, on
whose brilliant corollas the Diptera abound, either plundering from
every species indiscriminately, or attaching themselves to some
particular kind. They display the most wonderful instinct in their
maternal care, and employ the most varied and ingenious precautions to
preserve their progeny.
The Diptera, besides their variety and the number of their species,
are remarkable on account of their profusion. The myriads of flies
which rise from our meadows, which fly in crowds around our plants,
and around every organised substance from which life has departed,
some of which even infest living animals, are Diptera.
The profusion with which they are distributed over the face of the
globe, causes them to fulfil two important duties in the economy of
Nature. On the one hand, they furnish to insectivorous birds an
inexhaustible supply of food; on the other, they contribute to the
removal of all decaying animal and vegetable substances, and thus
serve to purify the air which we breathe. Their fecundity, the
rapidity with which one generation succeeds another, and their great
voracity, added to the extraordinary quickness of their reproduction,
are such that Linnæus tells us that three flies, with the generations
which spring from them, could eat up a dead horse as quickly as a lion
could.
These Diptera, which are worthy of so much attention, and deserve so
much study with regard to the part they play in the general economy of
Nature, are an object of fear and repulsion when one considers their
relations to us and other animals. Gnats and mosquitoes suck our
blood; the gad-fly and the species of Asilus attack our cattle. The
order Diptera is composed of a great number of families, which are
again divided into tribes, each comprising several genera. We shall
only notice the more remarkable genera of Diptera.
M. Macquart, the learned author of "L'Histoire Naturelle des
Diptères,"[11] divides this great class of insects into two principal
groups. In one of these groups, the antennæ are formed of at least six
joints, and the palpi of four or five: these are called Nemocera. In
the other, the antennæ consists only of three joints, and the palpi of
one or two: these are the Brachycera.
[11] "Suites à Buffon." 2 vols. 8vo.
The Nemocera may generally be distinguished from the other Diptera,
independently of the difference in the antennæ and palpi, by the
slenderness of the body, the smallness of the head, the shape of the
thorax, and the length of the feet and wings. The result of this
organisation is a graceful, light, and aerial form.
NEMOCERA.
Abounding everywhere, the Nemocera live, some on the blood of man and
animals, some on small insects, and others on the juices of fragrant
flowers. From [Greek: nêma], thread; [Greek: keras], horn.
In all climates, in every latitude, in the fields and woods, even in
our dwellings, they may be seen fluttering and plundering. The
Nemocera are divided into two families, that of the _Culicidæ_, of
which the gnat (_Culex_), which has a long, thin trunk, and a sucker
provided with six bristles, is a member; and that of the _Tipulidæ_,
which have a short thick trunk, and a sucker having two bristles.
[Illustration: Figs. 19 and 20.--The Gnat (_Culex pipiens_).]
We will begin our examination with the Gnat (_Culex pipiens_), of
which Réaumur, in his "Mémoires pour servir à l'Histoire des
Insectes," has given such a curious and complete history. "The gnat is
our declared enemy," says Réaumur, in the introduction to his memoir,
"and a very troublesome enemy it is. However, it is well to make its
acquaintance, for if we pay a little attention we shall be forced to
admire it, and even to admire the instrument with which it wounds us.
Besides which, throughout the whole course of its life it offers most
interesting matter of investigation to those who are curious to know
the wonders of Nature. During a period in its life the observer,
forgetting that it will at some time annoy him, feels the greatest
interest in its life-history."
As this is the case, let us explain the history of these insects,
which excite so much interest. The illustrious naturalist we have just
mentioned will be our guide.
The body of the gnat is long and cylindrical. When in a state of
repose one of its wings is crossed over the other. They present a
charming appearance when seen through a microscope, their nervures, as
well as their edges, being completely covered with scales, shaped like
oblong plates and finely striated longitudinally. These scales are
also found on all the segments of the body.
[Illustration: Fig. 21.--Antennæ of Gnat, magnified.]
[Illustration: Fig. 22.--Head of Gnat, magnified.]
The antennæ of the gnat, particularly those of the male, have a fine
feathery appearance (Fig. 21).
Their eyes, covered with network, are so large that they cover nearly
the whole of the head. Some have eyes of a brilliant green colour, but
looked at in certain lights they appear red. Fig. 22 shows the head of
the gnat with its two eyes, its antennæ, and trunk.
The instrument which the gnat employs for puncturing the skin, and
which is called the trunk (Fig. 23), is well worthy of our attention.
That which is generally seen is only the case of those instruments
which are intended to pierce our skin and suck our blood, and in which
they are held, as lancets and other instruments are held in a
surgeon's case. The case (Fig. 24) is cylindrical, covered with
scales, and terminates in a small knob. Split from end to end that it
may open, it contains a perfect bundle of stings. Réaumur tried to
observe, by allowing himself to be stung by gnats, what took place
during the attack. He forgot, in watching the operations of the
insect, the slight pain caused by the wound, soliciting it as a
favour, his only regret being not to obtain it when he wished.
Réaumur observed that the compound sting, which is about a line in
length, enters the skin to the depth of about three-quarters of a
line, and that during that time the case bends into a bow, until the
two ends meet. He noticed besides, that the trunk-case of certain
gnats was even more complicated than that which we have described. But
we will not dwell any longer on this point.
[Illustration: Figs. 23 and 24.--Trunk of Gnat, magnified.]
[Illustration: Figs. 25, 26, 27.--Lancets of the Gnat.]
Let us now try to give an idea of the construction and composition of
this sting, which, after piercing the skin, draws our blood.
According to Réaumur, the sting of the gnat is composed of five parts.
He acknowledges, however, that it is very difficult to be certain of
the exact number of these parts, on account of the way in which they
are united, and of their form. At the present day we know that there
are six. Réaumur, as also Leuwenhoek, thought he saw two in the form
of a sword blade with three edges. These have the points reversed, and
are serrated on the convex side of the bend (Fig. 25). To form an idea
of the shape of the other points, the reader should look at Figs. 26
and 27. He will then see that the gnat's sting is a sword in
miniature.
The prick made by so fine a point as that of the sting of the gnat
ought not to cause any pain. "The point of the finest needle," says
Réaumur, "compared to the sting of the gnat, is the same as the point
of a sword compared to that of the needle." How is it then that so
small a wound does not heal at once? How is it that small bumps arise
on the part that is stung? The fact is, that it is not only a wound,
but it has been imbued with an irritating liquid.
This liquid may be seen to exude, under different circumstances, from
the trunk of the gnat, like a drop of very clear water.
Réaumur sometimes saw this liquid even in the trunk itself. "There is
nothing better," he observes, "to prevent the bad effects of gnat
bites than at once to dilute the liquid they have left in the wound
with water. However small this wound may be, it will not be difficult
for water to be introduced. By rubbing, it will be at once enlarged,
and there is nothing to do but to wash it. I have sometimes found this
remedy answer very well."
The gnat is not always in the form of a winged insect, greedy for our
blood. There is a period during which they leave us in repose. This is
the larva period. It is in water, and in stagnant water in particular,
that the larva of the insect which occupies our attention is to be
found. It resembles a worm, and may be found in ponds from the month
of May until the commencement of winter.
[Illustration: Fig. 28.--Larva of the Gnat.]
If we desire to follow the larva of the gnat from the beginning, we
have only to keep a bucket of water in the open air. After a few days
this water will be observed to be full of the larvæ of the gnat (Fig.
28). They are very small, and come to the surface of the water to
breathe; for which purpose they extend the opening of a pipe, A, which
is attached to the last segment of the body, a little above the
surface. They are, consequently, obliged to hold their heads down. By
the side of the breathing-tube is another tube, B, shorter and thicker
than the former, nearly perpendicular to the body, its orifice being
the exterior termination of the digestive tube. At the anus it is
fringed with long hairs, having the appearance, when in the water, of
a funnel. At the end of the same tube, and inside the hair funnel, are
four thin, oval, transparent, scaly blades, having the appearance of
fins. They are placed in pairs, of which one emanates from the right
side, the other from the left.
These four blades or fins have the power of separating from each
other. Each segment of the abdomen has on both sides a tuft of hair,
and the thorax has three. The head is round and flat, and is provided
with two simple brown eyes. Round the mouth are several wattles,
furnished with hair, of which two of crescent-like form are the most
conspicuous. These tufts move with great quickness, causing small
currents of liquid to flow into the mouth, by means of which the
necessary food, microscopic insects and particles of vegetable and
earthy matter, is brought to the larva.
They change their skin several times during their continuance in this
state. This latter fact has been remarked by Dom Allou, a learned
Carthusian, "whose pleasure," says Réaumur, "consisted in admiring the
works of the Almighty, when not occupied in singing his praises." We
think it will be interesting to repeat the few lines which accompany
the mention made by Réaumur of this worthy Carthusian. They appear to
us to be well worth reading, even at the present day.
"If the pious monks who composed so many societies, possessed, like
Dom Allou, the love of observing insects, we might hope that the most
essential facts in the history of those little creatures would soon be
made known to us. What enjoyment more worthy of the calling they have
chosen could these pious men pursue than that which would place before
their eyes the marvellous creations of an Almighty Power? Even their
leisure would then incline them to adore that Power, and would furnish
them the means to make others do so who are occupied by too serious or
too frivolous employments."
After having changed its skin three times in a fortnight or three
weeks, the larva of the gnat throws off its covering for a fourth
time, and is no longer in the larva state. It is changed both in shape
and condition. Instead of being oblong, its body is shortened,
rounded, and bent in such a way that the tail is applied to the under
part of the head. This is the case when the animal is in repose; but
it is able to move and swim, and then, by bending its body and
straightening it again, propels itself through the water.
[Illustration: Fig. 29.--Pupa of the Gnat.]
In this new condition, that is to say, in the pupa state (Fig. 29), it
does not eat. It no longer possesses digestive organs, but it is
necessary, even more than before its metamorphosis, that it should
breathe atmospheric air. Besides, the organs of respiration are
greatly changed. During the time the insect was in the larva state, it
was through the long tube fixed to the posterior part that it received
or expelled the air; but in casting its skin it loses the tube, two
appendages resembling an ass's ears being for the pupa what the tube
was for the larva, the opening of these ears being held above the
surface of the water. From this pupa the perfect insect will emerge;
it is developed little by little, and the principal members may be
distinguished under the transparent membranous skin which envelopes
it.
When the insect is about to change from the pupa state, it lies on the
surface of the water, straightening the hind part of its body, and
extending itself on the surface of the water, above which the thorax
is raised. Before it has been a moment in this position, its skin
splits between the two breathing trumpets, the split increasing very
rapidly in length and breadth.
"It leaves uncovered," says Réaumur, "a portion of the thorax of the
gnat, easily to be recognised by the freshness of its colour, which is
green, and different from the skin in which it was before enveloped.
"As soon is the split is enlarged--and to do so sufficiently is the
work of a moment--the fore part of the perfect insect is not long in
showing itself; and soon afterwards the head appears, rising above the
edges of the opening. But this moment, and those which follow, until
the gnat has entirely left its covering, are most critical, and when
it is exposed to fearful danger. This insect, which lately lived in
the water, is suddenly in a position in which it has nothing to fear
so much as water. If it were upset on the water, and the water were to
touch its thorax or body, it would be fatal. This is the way in which
it acts in this critical position--As soon as it has got out its head
and thorax, it lifts them as high as it is able above the opening
through which they had emerged, and then draws the posterior part of
its body through the same opening; or rather that part pushes itself
forward by contracting a little and then lengthening again, the
roughness of the covering from which it desires to extricate itself
serving as an assistance.
"A larger portion of the gnat is thus uncovered, and at the same time
the head is advanced farther towards the anterior end of the covering;
but as it advances in this direction, it rises more and more, the
anterior and posterior ends of the sheath thus becoming quite empty.
The sheath then becomes a sort of boat, into which the water does not
enter; and it would be fatal if it did. The water could not find a
passage to the farther end, and the edges of the anterior end could
not be submerged until the other was considerably sunk. The gnat
itself is the mast of its little boat. Large boats, which pass under
bridges, have masts which can be lowered; as soon as the boat has
passed the bridge the mast is hoisted up by degrees, until it is
perpendicular. The gnat rises thus until it becomes the mast of its
own little boat, and a vertical mast also. It is difficult to imagine
how it is able to put itself in such a singular, though for it
necessary, position, and also how it can keep it. The fore part of the
boat is much more loaded than the other, but it is also much broader.
Any one who observes how deep the fore part of the boat is, and how
near the edges of its sides are to the water, forgets for the time
being that the gnat is an insect that he would willingly destroy at
other times. One feels uneasy for its fate; and the more so if the
wind happens to rise, particularly if it disturbs the surface of the
water. But one sees with pleasure that there is air enough to carry
the gnat along quickly; it is carried from side to side; it makes
different voyages in the bucket in which it is borne. Though it
is only a sort of boat--or rather mast, because its wings and legs
are fixed close to its body, it is perhaps, in proportion to the
size of its boat, a larger sail than one would dare to put on a
real vessel--one cannot help fearing that the little boat will
capsize. * * * As soon as the boat is capsized, as soon as the gnat
is laid on the surface of the water, there is no chance left for it.
I have sometimes seen the water covered with gnats which had perished
thus as soon as they were born. It is, however, still more extraordinary
that the gnat is able to finish its operations. Happily they do not last
long; all dangers may be passed over in a minute.
[Illustration: Fig. 30.--Gnats emerging.]
"The gnat, after raising itself perpendicularly, draws its two front
legs from the sheath, and brings them forward. It then draws out the
two next. It now no longer tries to maintain its uneasy position, but
leans towards the water; gets near it, and places its feet upon it;
the water is sufficiently firm and solid support for them, and is able
to bear them, although burdened with the insect's body. As soon as the
insect is thus on the water it is in safety; its wings are unfolded
and dried, which is done sooner than it takes to tell it, at length
the gnat is in a position to use them, and it is soon seen to fly
away, particularly if one tries to catch it."
[Illustration: Fig. 31.--Eggs of the Gnat, magnified.]
One more word about the gnat, whose life is full of such interesting
details.
The reader will perhaps not feel much pleasure in learning that the
fecundity of these insects is extraordinary. Many generations are born
in a single year, each generation requiring only three weeks or a
month to arrive at a condition to bring forth a new generation. Thus,
the number of gnats which comes into existence in the course of a
year is something fearful. Only a few days after the pupæ in a bucket
are transformed into gnats, eggs which have been left by the females
may be observed on the surface of the water in little clusters.
Many species of gnats, known as mosquitoes, are to be found in
America. All travellers speak of the sufferings endured by a stranger
in that country from the bites of these insects. One can only preserve
oneself from these cruel enemies during sleep by hanging gauze, called
a mosquito curtain, round the bed. Mosquito curtains are not only
necessary in America; during the hot season, in Spain, throughout the
whole of Italy, and a part of the south of France, it is necessary to
hang these curtains round the bed, if one wishes to obtain any sleep;
it is also a necessary precaution not to have a light in one's
bedchamber, as the sight of it at once attracts these dangerous
companions, whose buzzing and stinging prevent any possibility of
repose during the whole night. Such is our advice to people who travel
in the above-mentioned countries.
The _Tipulidæ_ have a narrow, elongated abdomen, and long and slight
limbs. The head is round, and the eyes, which are compound, are,
especially in the males, very large. The wings, which are long and
narrow, are sometimes held wide apart, sometimes horizontally, and
sometimes bent so as to form, as it were, a roof. The balancers are
naked and elongated; the abdomen long, cylindrical, and often
terminating in a club in the male, and in a point in the female. The
antennæ, which are longer than the head, are generally composed of
from fourteen to sixteen joints, and are sometimes in the form of a
comb or saw, sometimes furnished with hair, in form of plumes,
bunches, or in a whorl. The larvæ live on plants, in the fields, in
gardens, and sometimes in woods. The perfect insects, at first sight,
resemble gnats, but are without a trunk, or rather their trunk is
extremely short, terminating in two large lips, and the sucker is
composed of two fibres only.[12] The larger species of _Tipulæ_, which
are commonly known as "Daddy Longlegs," &c., and in France as
"_Tailleurs_" and "_Couturières_," are found in fields at the end of
September and commencement of October.
[12] The genus _Cecidomyia_, which belongs to this family,
presents the most extraordinary instance of agamo-genesis--or
reproduction without fertilisation by another individual--at
present known among insects. Until lately it was almost an
axiom with naturalists that no insect was capable of
reproduction until it had attained its adult or perfect state.
Several Continental observers, some of them without any
knowledge of the others' discoveries, have found that the
_larvæ_ of some of the species of this genus reproduce larvæ
resembling themselves in every respect; and what is still more
strange, these larvæ live in a free state within the parent
larvæ, feeding upon its tissues, and causing its ultimate
destruction.
A very interesting article on this subject will be found in the
_Popular Science Review_ for the 1st April, 1868. The larvæ of
a species (_Cecidomyia tritici_) frequently causes much injury
to the wheat.--ED.
"Although they sometimes fly a considerable distance," says Réaumur,
"when the sun is bright and hot, they generally do not go far; often,
indeed, only along the ground, or rather the top of the grass.
Sometimes they only use their wings to keep them above the level of
the herbage, and to take them along. Their legs, particularly the hind
ones, are disproportionately large. They are three times the length of
the body, and are to these insects what stilts are to the peasants of
marshy and inundated countries, enabling them to pass with ease over
the higher blades of grass."
One of the smaller species has been termed _culiciformis_, on account
of its resemblance to the gnat. The smaller are more active than the
larger species which we have mentioned. Not only do they fly more
rapidly, but there are some kinds which are continually on the wing.
In all seasons, even during the winter, at certain hours of the day,
clouds of small insects are seen in the air, which are taken for
gnats: they are _Tipulæ_. Their flight is worthy of attention; they
generally only rise and fall in the same vertical line. All these
flies come from larvæ, which resemble very elongated worms, having
scaly heads, generally furnished with two very small conical antennæ,
and certain other organs, for the purpose of obtaining food. Their
bodies are jointed without limbs, but nevertheless provided with
appendages which supply their place. The larvæ of the various species
are of very different habits. Some are aquatic, as that of _Tipula
culiciformis_, a small species which is very numerous in stagnant
waters.
It is necessary to say a few words about these worm-like larvæ, which
are extremely common. They are of a brilliant red colour, and inhabit
little oblong bent masses of earth, thickly pierced with holes. Each
hole allows a worm to extend its head, and the foremost part of its
body, out of the cell, which is made of light spongy matters, remains
of decayed leaves, &c. These larvæ are transformed into pupæ, in
the cell in which they have lived, during the larvæ state, losing by
this metamorphosis the scaly coverings of the head and of all the
exterior parts. They pass into the pupa state, and have the thorax
provided with dainty plumes, which probably assist in the action of
respiration. This pupa is very active and quick in its movements in
the water. When the moment comes for its last metamorphosis, it throws
off its feathery covering in much the same manner as the gnat.
Fig. 32 represents _Tipula oleracea_ in the different stages of larva,
pupa, and perfect insect.
[Illustration: Fig. 32.--Daddy Longlegs (_Tipula oleracea_).]
Other species of small _Tipulæ_ have aquatic larvæ very similar to
those which we have described. Réaumur remarked that each of these
worms is lodged in a thick mass, convex at the top, formed of a
transparent and adhesive white jelly. The larvæ of the larger _Tipulæ_
are not aquatic, but are of different habits, and live under the
ground; all soil which is not frequently turned is suitable to them,
but they are to be found especially in low damp meadows.
Réaumur saw large districts of grassy swamps in Poictou, which, in
certain years, furnished very little grass for the cattle, on account
of the ravages caused by these larvæ. They had also much injured the
harvest in the same districts during those years.
These larvæ appear to require no other food than vegetable mould.
Their excrements are, in fact, according to Réaumur, nothing else
than dried earth, from which the stomach and intestines of the insect
have withdrawn all nourishing matter.
Old trees have often hollow cavities occasioned by the decay of the
trunk. When these cavities are old, their lower parts are full of a
sort of mould, which is in fact half-decayed wood. It is there that
the _Tipulæ_ often lay their eggs. Réaumur frequently found the larvæ
in the trunks of elms or willows, and also in the fleshy parts of
certain kinds of mushrooms. He carefully observed the habits of one,
which lived under the covering of a mushroom, the Oak agaric
(_Agaricus quercinus_). This larva is round, grey, and resembles an
earth-worm. It does not walk, but crawls; and the places where it
stops, or which it passes over, are covered with a sort of brilliant
slime, like that left by the snail or slug.
M. Guérin-Méneville has published some very interesting remarks on the
migrations of the larvæ of a particular kind of _Tipula_, known by the
name of _Sciara_. We will borrow from that entomologist the following
curious details, which will initiate us into one of the most wonderful
phenomena in the whole history of insects. These small larvæ are
without feet, hardly five lines in length, and about the third of a
line in diameter. They are composed of thirteen segments, and have
small black heads.
In some years, during the month of July, may be found on the borders
of forests in Norway and Hanover, immense trains of these larvæ,
formed by the union of an innumerable quantity fixed to each other by
a sticky substance. These collections of larvæ resemble some sort of
strange animal of serpent-like form, several feet long, one or two
inches in thickness, and formed by the union of an immense number,
which cling to each other by thousands, and move on together. The
whole society advances thus with one accord, leaving a track after it
on the ground, as a material indication of its presence.
These strange collections of living creatures form societies,
sometimes only a few yards long; but at other times it happens that
they form bands from ten to twelve yards in length, of the breadth of
a hand and the thickness of a thumb. M. Guérin-Méneville observed
columns as many as thirty yards in length. These troops advance as
slowly as a snail, and in a certain direction. If they encounter an
obstacle--as a stone, for instance--they cross over it, turn round it,
or else divide into two sections, which reunite after the obstacle is
passed. If a portion of the column be removed so as to divide it into
two parts, it is quickly reunited, as the hindmost portion soon joins
that which precedes it. Lastly, if the posterior part of this living
ribbon be brought into contact with the anterior, a circle is formed,
which turns round and round on the same ground for a long time,
sometimes even for a whole day, before breaking, and continuing to
advance. They are never met with in bad weather, but only when the sun
is warm.
The curious and astonishing phenomenon of an assembly of larvæ without
feet, advancing with an equal movement resulting from the individual
motion of thousands of little worms, was remarked for the first time,
in 1603, by Gaspard Schwenefelt. This naturalist says that the
inhabitants of Siberia consider this phenomenon as an indication of a
bad harvest if they go towards the mountains; whereas, if they descend
towards the plains, it is the sign of a good one. In 1715 Jonas Ramus
mentioned the same phenomenon, recalling a superstition attached to it
by the peasants of Norway. This writer informs us that the peasants of
that country, on meeting one of these moving columns, throw down their
belts or waistcoats on the ground before it. If the _orme-drag_ (that
is the name given to the moving column) crosses over this obstacle, it
is a good sign; but on the other hand, if the column turns round the
obstacle, instead of crossing it, some mischief may be expected.
The same animals were observed in 1845 at Birkenmore, near Hefeld, by
M. Rande, Royal Inspector of the Forests of Hanover.
M. Guérin-Méneville is of opinion that these larvæ, which exist in
great numbers in certain districts, sometimes devour all the nutritive
substances contained in the ground. After having done so, they are
obliged to come out of it, in order to seek at a distance a place
where they will find food, or perhaps only a suitable place to undergo
their metamorphosis. It is then that this singular journey commences.
As regards the uniting of these myriads of individuals into columns,
M. Guérin-Méneville thinks that it can be explained by the necessity
these insects feel for mutual protection against the drying effect of
the atmosphere when they are forced to leave the ground. United into
masses, and moistened by the glutinous matter which connects them,
they can leave their former place of abode without danger; if each
were by itself, they would soon perish. Here, as in other cases, union
is strength; and the strength of these larvæ lies in this protecting
moisture. However it may be explained, the migration of these troops
of insects are among the most astonishing phenomena of Nature.
BRACHYCERA.
The Brachycera, from [Greek: brachus], "short;" and [Greek: keras], "a
horn"--these Diptera having short antennæ--are divided into four
groups. In this subdivision the sucker is composed of six bristles.
Amongst other families it includes that of the _Tabanidæ_; the insects
belonging to which family are of remarkable strength, and possessed of
daring and courage in the highest degree. Their wings are provided
with powerful muscles, their feet are very strong, and their trunk is
provided with six flat, sharp lancets. Distributed over the entire
world, their instinct is everywhere the same, it is the desire for
blood, at least in the females; for the males are not so warlike, they
do no harm, but live on the juices of flowers. They are chiefly found
in woods and pastures, and during the hottest part of the day in
summer may be seen flying about seeking for their prey.
M. de Saint-Fargeau has described the manner in which the males fly.
They may be seen flying hither and thither in the glades of woods,
remaining for some time suspended in the air, then darting quickly and
suddenly away a yard or two, again taking up the same immovable
position, and in each of these movements turning the head to the
opposite way from that in which they are going. This naturalist is
certain that on these occasions they are watching for the females,
which they dart upon. When they have succeeded in doing so, they rise
so high as to be out of sight.
To this group belongs the genus _Tabanus_.
The first species we shall mention, _Tabanus autumnalis_ (Fig. 33), a
common species, is eight or nine lines in length, and of blackish
colour. The palpi, the face, and the forehead are grey; the antennæ
black; the thorax grey, striped with brown; the abdomen spotted with
yellow; the legs of a yellowish white; and the outer edge of the wings
brown.
Another species (_Tabanus bovinus_) is twelve lines in length, and of
a blackish brown. The palpi, the face, and the forehead are yellow;
the antennæ black, with a whitish base; the thorax, covered with
yellow hair, is striped with black; the posterior edge of the segments
of the abdomen pale yellow; the legs yellowish, with the extremities
black, and the exterior edge of the wings yellow. This species is
frequently met with in woods.
A third species, _Chrysops cæcutiens_ (Fig. 34), which belongs to the
same family, and of which the generic name _Chrysops_ signifies
golden-eyed, torments horses and cattle very much by biting them round
the eyes. Its thorax is of a yellowish colour, striped or spotted with
black; the abdomen yellow, and the eyes golden.
In the next group of the Brachycera the sucker is composed of four
bristles, and the antennæ generally terminate in a point which appears
to be rather a development than an appendage.
This group includes a number of genera, but the following only possess
sufficient interest to claim our attention. From the _Tanystomæ_ we
select the families of the _Asilidæ_, _Empidæ_, and _Bombylidæ_. As
types of the _Brachystomæ_ we select the _Leptidæ_ and _Syrphidæ_.
[Illustration: Fig. 33.--Tabanus autumnalis.]
[Illustration: Fig. 34.--Chrysops cæcutiens.]
The chief characteristic of the _Asilidæ_ is strength. All their
organs combine to produce this quality, which they display only too
much, being as formidable to cattle as the _Tabani_, but even
surpassing those insects in natural cruelty.
The _Asilidæ_ unceasingly attack other insects, and even those of
their own kind. Their trunk is strong; one of the fibres of the sucker
is furnished with small points, turned back, which are intended to
hold firmly to the body into which it has entered. They carry on their
devastations in the glades of woods and on sunny roads.
We will mention in this group _Asilus crabroniformis_ (Fig. 35), an
insect ten to twelve lines long, having a yellow head, black antennæ,
and thorax of a brownish yellow. The three first segments of the
abdomen are black, the second and third having a white spot on each
side, the remaining segments are yellow. The wings are yellowish,
spotted with black on the inner and hind margin. This species is
common over the whole of Europe, and lives at the expense of
caterpillars and other insects, of which it sucks the blood with the
greatest voracity.
[Illustration: Fig. 35.--Asilus crabroniformis.]
[Illustration: Fig. 36.--Bombylius major.]
The _Empidæ_ live in the same way as the _Asilidæ_, but the males are
chiefly nourished by the juices of flowers.
"They wage war on other insects," says M. Macquart, in his "Histoire
Naturelle des Diptères," "either when flying or running, and they
seize their victims with their feet, which are formed in various ways,
and well adapted for their purpose, but it is in the air that their
hunting, as well as their amours, chiefly take place. They unite
together in numerous companies, which during fine summer evenings
whirl like gnats about the water's edge. A singular observation,
however, that I have made on the _Empis_, is, that among the thousands
of pairs that I have seen resting on hedges and bushes, nearly all the
females were occupied in sucking an insect; some had hold of small
_Phryganeæ_,[13] others of _Ephemeræ_,[14] and the greater part of
_Tipulæ_."
[13] The insects produced from the caddis or case-worm.--ED.
[14] May-fly family.--ED.
The _Empidæ_ have the trunk bent down, and resembling the beak of a
bird; but the _Bombylidæ_, on the contrary, have the trunk extended
straight in front.
The typical genus which has given its name to this latter group is
easily to be recognised by the elegance of the fur which covers its
body, the slenderness of its feet, and the length of its wings, which
extend horizontally on each side of the body.
Much more common in hot climates than in the North, these insects, the
larvæ of which are not yet known, take flight in the middle of the
day, when the sun's rays are hottest. They fly very fast, making a
dull buzzing sound, and hover over flowers, from which they draw the
juices without settling.
Fig. 36 represents the _Bombylius major_, which is common enough
throughout the whole of Europe. This insect is from four to six lines
long, black, with yellow fur; the feet light yellow; and the wings
have the edges bordered with a sinuous brown band.
The genus _Anthrax_, belonging to this family, has a different form to
_Bombylius_. The body is much less hairy; the trunk is short and
concealed in the mouth; the wings, which are very large, are clothed,
at least in the principal genus, in a garb of mourning, sufficiently
remarkable, in which the combinations of black and white are admirably
diversified.
"Here," says M. Macquart, "the line which separates the two colours is
straight; there it represents gradations, in other cases it is deeply
sinuous. Sometimes the dark part shows transparent points, or the
glassy part dark spots. This sombre garb, added to the velvet black of
the body, gives the Anthrax a most elegant appearance; and while
resting on the corolla of the honeysuckle and hawthorn to suck the
juice, forms a most striking contrast, and sets forth its beauty no
less than that of those lovely flowers."
_Anthrax sinuata_ is common in Europe.
The family of the _Syrphidæ_ includes three remarkable types, which we
cannot pass over in silence. They are _Vermileo_, _Volucella_, and
_Helophilus_.
_Vermileo de Geeri_ (Fig. 37), which inhabits the central and southern
parts of France, is four or five lines in length. Its face is white;
its forehead grey, bordered with black; the thorax of a yellowish
grey, with four brown stripes in the male; the abdomen light yellow,
spotted with black; and the wings glassy.
[Illustration: Fig. 37.--Vermileo de Geeri.]
[Illustration: Fig. 38.--A species of Volucella.]
The larva of the _Vermileo_ has a thin cylindrical body, capable of
bending itself in every direction; a conical head, armed with two
horny points; and the last segment elongated, flat, elevated, and
terminated by four hairy tentacles; at the sides of the fifth segment
may be observed a little angle, from which projects a horny retractile
point.
It is of very singular habits. It makes a small tunnel in the sand,
having a conical mouth, where it waits, like the spider, immovable. As
soon as an insect falls into the hole, it raises its head, and
squeezing its prey in the folds of its body, devours it, and
afterwards throws out the skin. It lives in this way for at least
three years before attaining the perfect state.
The _Volucellæ_ (Fig. 38) have a strong resemblance to the humble-bee.
Certain kinds make use and abuse of this resemblance to introduce
themselves fraudulently into its nests, and to deposit their eggs
therein. When these eggs have hatched, the larvæ, which have the mouth
armed with two mandibles, devour the larvæ of their hosts, the bees.
This is the return they make for the hospitality they have received!
[Illustration: Fig. 39.--A species of Helophilus.]
[Illustration: Fig. 40.--Larvæ of a Helophilus.]
The _Helophili_ (Fig. 39) deserve to be mentioned here on account of
the singular form of many of their larvæ. The head is thick, fleshy,
and varying a little in form. But the point by which they are easily
to be distinguished from most other larvæ is, that they have always
very long tails, sometimes, indeed, out of proportion to the length of
the body. Réaumur called these larvæ "vers à queue de rat;" they are
known in England as rat-tailed maggots, and their habits are aquatic.
Having placed some of them in a bason of water, Réaumur saw that they
kept in a perpendicular position at the bottom of the bason and
parallel to one another, the extremities of their tails being on the
surface of the water. He then increased the depth of the water by
degrees; and, as it got deeper, observed that the tail of each worm
became longer. These tails, which at first were only two inches long,
at last attained to five.
It will be remarked that the body of each worm does not exceed five
lines in length. The tail is a peculiar organ, by the aid of which the
worm breathes, although its body may be covered by water to the depth
of several inches. It is composed of two tubes, one of which shuts
into the other, like a telescope. Réaumur calls it the breathing tube.
It terminates in a little brown knob, in which, according to Réaumur,
are two holes for the purpose of receiving the air, and which have
five little tufts of hair, which float on the surface of the water.
When the time comes for the metamorphosis of these worms, they come
out of the water and bury themselves in the earth; the skin then
hardens and becomes a sort of cocoon. In this cocoon the insect loses
the form of a worm, and takes by degrees that of the pupa, which it
keeps until circumstances cause it to throw off its last coverings,
and to appear in the winged state.
What an eventful life! what a life full of changes and turns of
fortune is that of these insects, which pass the first and longest
period of their existence under water, another part of their life
under the ground, and, finally, after having existed in these two
elements, enjoy, high in the air, the pleasures of flight!
The third group of Brachycera is that of the _Dichæta_; that is, those
flies having two-fibred suckers. Among these are classed the
_OEstri_, the _Conopes_, and the flies properly so called.
The genus _OEstrus_, the Gad, Bot-fly, or Breeze, comprises those
formidable insects which attack the horse, the sheep, and the ox.[15]
The labours of Réaumur, in his admirable Memoirs, and those of M.
Joly, Professor of Zoology to the Faculté des Sciences de Toulouse,
who published some most valuable researches on this subject, in 1846,
will guide us in the following brief explanation.
[15] Mr. Bates, in his interesting "Naturalist on the Amazons,"
mentions an _OEstrus_ as occurring in those regions, which
deposits its eggs in the human flesh, the larva causing a
swelling which resembles a boil.--ED.
The following is the description given by M. Joly of the Gad-fly
(_OEstrus equi_) represented in Figs. 41, 42, which are taken from a
drawing which accompanies that naturalist's Memoirs.
The head of this insect is large and obtuse; the face light yellow,
with whitish silky fur; the eyes blackish; the antennæ ferruginous;
the thorax grey; and the abdomen of a reddish yellow, with black
spots. The wings are whitish, not diaphanous, with a golden tint, and
divided by a winding band of blackish colour. The feet are palish
yellow.
[Illustration: I. A Herd of Horses attacked by Gad-flies (_OEstrus
equi_).]
[Illustration: Fig. 41.--Horse-fly, male (_OEstrus_ [_gasterophilus_]
_equi_).]
[Illustration: Fig. 42.--Horse-fly, female (_OEstrus_ [_gasterophilus_]
_equi_).]
This species is found in France, in Italy, and also in the East,
especially in Persia, and rarely in England. During the months of July
and August the _OEstrus_ frequents pastures, and deposits its eggs
chiefly on the shoulders and knees of horses (PLATE I.). In order to
do this, the female suspends herself in the air for some seconds over
the place she has chosen, falls upon it, and with her abdomen bent,
sticks her eggs to the horse's hairs by means of a glutinous liquid
with which they are provided, and which soon dries. This is repeated
at very short intervals. It often happens that from four to five
hundred eggs are thus deposited upon the same horse. Guided by a
marvellous instinct, the female _OEstrus_ generally places her eggs
on those parts of the horse's body which can be most easily touched
with the tongue, that is, at the inner part of the knees, on the
shoulders, and rarely on the outer part of the mane.
[Illustration: Fig. 43.--Eggs of the Gad-fly (_OEstrus_
[_gasterophilus_] _equi_) deposited on the hairs of a horse.]
The eggs of the _OEstrus_, which are white and of conical form,
adhere to the horse's hair, as shown in Fig. 43. They are furnished
with a lid, which at the time of hatching opens, to allow the exit of
the young larva, which takes place, according to M. Joly, about twenty
days after they are deposited. In fact, it is not in the egg state,
but really in that of the larva, that the horse, as we shall explain,
takes into his stomach these parasitical guests, to which Nature has
allotted so singular an abode. When licking itself, the horse carries
them into its mouth, and afterwards swallows them with his food, by
which means they enter the stomach. It is a remarkable fact that it is
sometimes other insects, as the _Tabania_ for instance, that by their
repeated stinging cause the horse to lick himself, and thus to receive
his most cruel enemy. In the perilous journey they have to perform
from the skin of the horse to his stomach, many of the larvæ of the
_OEstrus_, as may be supposed, are destroyed, ground by the teeth of
the animal, or crushed by the alimentary substances. There is hardly
one _OEstrus_ in fifty that arrives safely in the stomach of the
horse; and yet if one were to open a horse which had been attacked by
the _OEstri_, the stomach would be nearly always found to have many
of the larvæ sticking to its inside. Fig. 44, taken from a drawing
which accompanies M. Joly's Memoirs, represents the state of a horse's
stomach attacked by the Gad-fly larvæ.
[Illustration: Fig. 44.--Portion of the stomach of the horse, and
larvæ of OEstrus (gasterophilus) equi.]
The larvæ are of a reddish yellow, and each of their segments is armed
at the posterior edge with a double row of triangular spines, large
and small alternately, yellow at the base, and black at the point,
which is always turned backwards. The head is furnished with two
hooks, which serve to fasten the larva to the internal coats of the
stomach. The spines with which the whole surface of the body is
furnished contribute to fix it more perfectly, preventing the
creatures, by the manner in which they are placed, from being carried
away by the food which has gone through the first process of
digestion.
It is probable that this larva, so singularly deposited, is nourished
by the mucus secreted by the mucous membrane of the stomach, and that
it breathes the air which the horse swallows with its food during the
process of deglutition. It must be acknowledged, however, that it is
in the midst of a gaseous atmosphere which is very unhealthy, for
nearly all the gases generated in the stomach of the horse are fatal
to man and to the generality of animals, as they consist of nitrogen,
carbonic acid, sulphuretted hydrogen, and carburetted hydrogen. To
explain how the insect can live under such circumstances, M. Joly has
suggested the following ingenious hypothesis:--
"When the stomach which the larva inhabits," says this learned
naturalist, "contains only oxygen, or air that is nearly pure, the
insect opens the two lips of the cavity which contains the spiracles,
and breathes at its ease. When the digestion of the alimentary
substance generates gas which is unfit for respiration, or when the
spiracles run the risk of being obstructed by the solid or liquid
substances contained in the stomach, it shuts the lips, and continues
to live on the air contained in its numerous tracheæ."
"Whatever may be the value of this explanation," adds M. Joly, "it is
nevertheless very curious to see an insect pass the greater part of
its life in an atmosphere which would be instantly fatal to most
animals, and in an organ where, under the government of life, chemical
processes bring about the most wonderful changes of the food into the
substance of the animal itself. But how can the insect itself resist
the action of these mysterious powers, and remain alone intact in the
midst of all these matters which are unceasingly changing and
decomposing? This is another question which it is difficult, or rather
impossible, to explain in the present state of science; another enigma
which humbles our pride, and of which He who has created both man and
the worm alone knows the secret."
Arrived at a state of complete development, the larva of the
_OEstrus_ imprisoned in the stomach of the horse leaves the membrane
to which it has been fixed, then directing the anterior part of its
body towards the pyloric opening of the stomach, allows itself to be
carried away with the excrementitious matter. It traverses, mixed with
the excrementary bolus, the whole length of the intestinal canal,
leaves it by the anal orifice, and on touching the ground at once
seeks a suitable place to go through the last but one of its
metamorphoses.
The skin then gets thick, hardens, and becomes black. All the organs
of the animal are composed of a whitish amorphous pulp, which soon
assumes its destined form, and the insect becomes perfect. It then
lifts a lid at the anterior part of its cocoon, emerges, dries its
wings, and flies off.
[Illustration: Fig. 45.--Bot-fly (_OEstrus bovis_).]
The Bot-fly (_OEstrus bovis_, Fig. 45) has a very hairy body, large
head, the face and forehead covered with light yellow hair, the eyes
brown, and the antennæ black. The thorax is yellow, barred with black;
the abdomen of a greyish white at the base, covered with black hair on
the third segment, and the remainder of an orange yellow; the wings
are smoky brown.
As soon as the cattle are attacked, they may be seen, their heads and
necks extended, their tails trembling, and held in a line with the
body, to rush to the nearest river or pond, while such as are not
attacked disperse (PLATE II.). It is asserted that the buzzing alone
of the _OEstrus_ terrifies a bullock to such an extent as to
render it unmanageable. As for the insect, it simply obeys its
maternal instinct, which commands it to deposit its eggs under the
skin of our large ruminants.
[Illustration: II. A Herd of Cattle attacked by Bot-flies (_OEstrus
bovis_).]
Let us now explain how the eggs of the _OEstrus_, deposited in the
skin of the bullock, accommodate themselves to this strange abode. The
mother insect makes a certain number of little wounds in the skin of
the beast, each of which receives an egg, which the heat of the animal
serves to bring forth. It is a natural parallel to the artificial way
which the ancient Egyptians invented of hatching the eggs of domestic
fowls, and which has been imitated badly enough in our day.
Directly the larva of the Bot-fly is out of the egg and lodged between
the skin and the flesh of its host, the bullock, it finds itself in a
place perfectly suitable to its existence. In this happy condition the
larva increases in growth, and eventually becomes a fly in its turn.
Those parts of the animal's body in which the larvæ are lodged are
easily to be recognised, as above each larva may be seen an elevation,
a sort of tumour, termed a bot--a bump, as Réaumur calls it, comparing
it more or less justly to the bump caused on a man's head by a severe
blow.
Fig. 46, taken from a drawing in Réaumur's Memoirs, represents the
bots of which we speak.
The country people are well aware of the nature and cause of these
bots. They know that each one contains a worm, that this worm comes
from a fly, and that later it will be transformed into a fly itself.
Each of these bots has in its interior a cavity, occupied by a larva,
which, as well as the bot, increases in size as the larva becomes
developed.
It is generally on young cows or young bullocks--in fact, on cattle of
from two to three years of age--that these tumours exist, and they are
rarely to be seen on old animals. The fly, which by piercing the skin
occasions these tumours, always chooses those whose skin offers little
resistance. Each tumour is provided with a small opening, by which the
larva breathes.
In order to examine the interior of the cavity, Réaumur opened some of
these tumours, either with a razor or a pair of scissors. He found
them in a most disgusting state. The larva is lodged in a regular
festering wound, matter occupying the bottom of the cavity, and the
head of the worm is continually, or almost continually, plunged in
this liquid. "It is most likely very well off there," says Réaumur;
and he adds that this matter appears to be the sole food of the
larva.
"The position of a horned beast," observes the great naturalist,
"which has thirty or forty of these bumps on its back, would be a very
cruel one, and a terrible state of suffering, if his flesh were
continually mangled by thirty or forty large worms. But it is probable
they cause no suffering, or at least very little, to the large animal.
Besides," continues Réaumur, "those cattle whose bodies are the most
covered with bumps, not only show no signs of pain, but it does not
appear that they are prejudicial to them in any way."
[Illustration: Fig. 46.--Bumps produced on Cattle by the larvæ of the
Bot-fly.]
Réaumur tried to discover how the larva, when arrived at its full
growth, succeeds in leaving its abode, as the opening is smaller than
its own body.
"Nature," says Réaumur, "has taught this worm the surest, the
gentlest, and the most simple of methods, the one to which surgeons
often have recourse to hold wounds open, or to enlarge them. They
press _tents_ into a wound they wish to enlarge. Two or three days
before the worm wishes to come out, it commences to make use of its
posterior part as a tent, to increase the size of its exit from its
habitation. It thrusts it into the hole and draws it out again many
times in the course of two or three days, and the oftener this is
repeated, the longer it is able to retain its posterior end in the
opening, as the hole becomes larger. On the day preceding that on
which the worm is to come out, the posterior part is to be found
almost continually in the hole. At last, it comes out backwards, and
falls to the ground, when it gets under a stone, or buries itself in
the turf; remaining quiet and preparing for its last transformation.
Its skin hardens, the rings disappear, and it becomes black.
Thenceforth the insect is detached from the outer skin, which forms a
cocoon, or box. At the front and upper part of the cocoon is a
triangular piece, which the fly gets rid of when it is in a fit state
to come into the open air."
Fig. 47, taken from drawings in Réaumur's Memoirs, represents the
imago of the _OEstrus_ leaving the cocoon.
[Illustration: Fig. 47.--Imago of Bot-fly emerging.]
[Illustration: Fig. 48.--Ovipositor of the Bot-fly (_OEstrus bovis_).]
The reader is, most likely, desirous to know with the aid of what
instrument the _OEstrus_ is able to pierce the thick skin of the ox.
The female only is possessed of this instrument, which is situated in
the posterior extremity of the body. It is of a shiny blackish brown
colour, and as it were covered with scales. By pressing the abdomen of
the fly between one's two fingers it is thrust out. Réaumur observed
that it was formed of four tubes, which could be drawn the one into
the other, like the tubes of a telescope (Fig. 48). The last of these
appears to terminate in five small scaly knobs, which are not placed
on the same line, but are the ends of five different parts. Three of
these knobs are furnished with points, which form an instrument well
fitted to operate upon a hard thick skin. United together, they form a
cavity similar to that of an auger, and terminating in the form of a
spoon.
The Gad-fly, or Breeze-fly of the sheep, _OEstrus_ (_Cephalemyia
ovis_), has obtained notoriety on account of its attacking those
animals.
Even at the sight of this insect the sheep feels the greatest terror.
As soon as one of them appears, the flock becomes disturbed, the sheep
that is attacked shakes its head when it feels the fly on its nostril,
and at the same time strikes the ground violently with its fore-feet;
it then commences to run here and there, holding its nose near the
ground, smelling the grass, and looking about anxiously to see if it
is still pursued.
[Illustration: Fig. 49.--Cephalemyia ovis.]
It is to avoid the attacks of the _Cephalemyia_ that during the hot
days of summer sheep lie down with their nostrils buried in dusty
ruts, or stand up with their heads lowered between their fore-legs,
and their noses nearly in contact with the ground. When these poor
beasts are in the open country, they are observed assembled with their
nostrils against each other and very near the ground, so that those
which occupy the outside are alone exposed (PLATE III.). The
_Cephalemyia ovis_ (Fig. 49) has a less hairy head, but larger in
proportion to the size of its body than the Gad-fly (_Gasterophilus
equi_). Its face is reddish; its forehead brown with purple bars; its
eyes of a dark and changing green; its antennæ black, its thorax
sometimes grey, sometimes brown, bristling with small black
tubercles; the abdomen white, spotted with brown or black; and the
wings hyaline.
[Illustration: III. Sheep attacked by _Cephalemyia ovis_.]
The _Cephalemyia_ (_OEstrus_) _ovis_ is to be found in Europe,
Arabia, Persia, and in the East Indies. It lays its eggs on the edges
of the animal's nostrils, and the larva lives in the frontal and
maxillary sinuses. It is a whitish worm, having a black transverse
band on each of its segments. Its head is armed with two horny black
hooks, parallel, and capable of being moved up and down and laterally.
Underneath, each segment of the body has several rows of tubercles of
nearly spherical form, surmounted by small bristles having reddish
points, and all of them bent backwards. "These points," says M. Joly,
"probably serve to facilitate the progress of the animal on the smooth
and slippery surfaces of the mucous membranes to which it fixes itself
to feed, and perhaps also to increase the secretion of these membranes
by the irritation occasioned by the bristles with which they are
furnished."[16]
[16] "Recherches sur les OEstrides en général, et
particulièrement sur les OEstres qui attaquent l'homme, le
cheval, le boeuf, et le mouton." Par N. Joly, Professeur à la
Faculté des Sciences de Toulouse. P. 63. Lyons, 1846.
Fixed by means of these hooks to the mucous membrane, which it
perforates, the larva nourishes itself with mucus, and lives in this
state, according to M. Joly, during nearly a whole year. At the end of
this time it comes out, following the same course by which it entered,
falls to the ground, and burying itself to the depth of a few inches,
is transformed into a pupa. The cocoon is of a fine black colour.
Thirty or forty days after its burial it emerges in the perfect state,
and detaching the lid at the anterior end of the cocoon by the aid of
its head, which has increased considerably in size, takes flight.
[Illustration: Fig. 50.--Conops.]
Notwithstanding the formidable appearance of their trunks, the habits
of the perfect _Conopes_ (Fig. 50) are very quiet. In the adult state
they are only to be seen on flowers, of which they suck the honeyed
juice. But with their larvæ the case is otherwise. These latter live
as parasites on the humble-bees (_Bombi_). Latreille saw the _Conops
rufipes_ issue in the perfect state from the body of a humble-bee,
through the intervals of the segments of the abdomen.
The _Mucides_ form that great tribe of Diptera commonly known as
flies, and which are distributed in such abundance over the whole
world. Faithful companions of plants, the flies follow them to the
utmost limits of vegetation. At the same time they are called upon by
Nature to hasten the dissolution of dead bodies. They place their eggs
in the carcases of animals, and the larvæ prey upon the corrupt flesh,
thus quickly ridding the earth of those fatal causes of infection to
its inhabitants. The organs of these insects are also infinitely
modified, in order to adapt them to their various functions.
[Illustration: Fig. 51.--Echinomyia grossa.]
M. Macquart divides the _Muscides_ into three sections--the
_Creophili_, the _Anthomyzides_, and the _Acalyptera_.
The _Creophili_ have the strongest organisation; their movements and
their flight are rapid. The greater part feed on the juices of
flowers, some on the blood or the humours of animals. Some deposit
their eggs on different kinds of insects, others on bodies in a state
of decomposition, some again are viviparous. The insects of the genus
_Echinomyia_, for instance (Fig. 51), derive their nourishment from
flowers. They deposit their eggs on caterpillars, and the young larvæ
on hatching penetrate their bodies and feed on their viscera. How
surprised, sometimes, is the naturalist, who, after carefully
preserving a chrysalis, and awaiting day by day the appearance of the
beautiful butterfly of which it is the coarse and mysterious envelope,
sees a cloud of flies emerge in place of it!
But there is another singular manoeuvre performed by some of the
species of the Diptera with which we are at present occupied to
prepare an abundant supply of provision for their larvæ as soon as
they are hatched. The following are the means they employ. It is well
known that certain fossorial Hymenoptera carry their prey--other
insects which they have caught, weevils, flies, &c., and which they
intend should serve as food for their own larvæ--into their
subterranean abodes. These Diptera, spying a favourable moment, slip
furtively into their retreats, and deposit their eggs on the very food
which was intended for others. Their larvæ, which are soon hatched,
make great havoc among the provisions gathered together in the cave,
and cause the legitimate proprietors to die of starvation.
"This instinct," says M. Macquart, "is accompanied by the greatest
agility, obstinacy, and audacity, which are necessary to carry on this
brigandage; and, on the other hand, the Hymenoptera, seized with fear,
or stupefied, offer no resistance to their enemies, and although they
carry on a continual war against different insects, and particularly
against different _Muscides_, they never seize those of whom they have
so much to complain, and which, nevertheless, have no arms to oppose
them with."
The _Sarcophagæ_ are a very common family of Diptera, and are chiefly
to be found on flowers, from which they steal the juice. The females
do not lay eggs, but are viviparous.
Réaumur, with his usual care, observed this remarkable instance of
viviparism proved in a fly, which seeks those parts of our houses
where meat is kept to deposit its larvæ. This fly is grey, its legs
are black, and its eyes red.
When one of them is taken and held between the fingers, there may
often be seen a small, oblong, whitish, cylindrical worm come out of
the posterior part of the body, and shake itself in order to disengage
itself thoroughly. It has no sooner freed itself than the head of
another begins to show. Thirty or forty sometimes come out in this
manner, and, on pressing the abdomen of the fly slightly, more than
eighty of these larvæ may sometimes be made to come out in a short
space of time. If a piece of meat be put near these worms, they
quickly get into it, and eat greedily. They grow rapidly, attaining
their full size in a few days, and make a cocoon of their skin, from
which in a certain time the imago issues. If the body of one of these
ovo-viviparous flies (for the eggs hatch within the parent) be opened,
a sort of thick ribbon of spiral form is soon seen. This ribbon
appears at first sight to be nothing but an assemblage of worms,
placed alongside of and parallel to one another.
Each worm has a thin white membranous envelope, similar to those
light spiders' webs which float about in autumn, which the French call
_fils de la vierge_, and we denominate _gossamer_.
The fecundity of this fly is very great, for, in the length of a
quarter of an inch, the envelope in which these small worms are
enclosed contains 2,000 of them. Therefore this ribbon, being two
inches and a half long, contains about 20,000 worms.
The members of the genus _Stomoxys_, though nearly related to the
house-fly, differ from it very much in habits. They live on the blood
of animals. The _Stomoxys calcitrans_ is very common in these
climates. Its palpi are tawny yellow, antennæ black, thorax striped
with black, abdomen spotted with brown, and its trunk hard, thin, and
long. It deposits its eggs on the carcases of large animals.
The Golden Fly, _Lucilia Cæsar_, lays its eggs on cut-up meat, or on
dead animals. It is only three or four lines in length, of a golden
green, with the palpi ferruginous, antennæ brown, and feet black.
[Illustration: Fig. 52.--Lucilia hominivorax.]
A species of this genus, the _Lucilia hominivorax_, has lately
obtained a melancholy notoriety. We are indebted to M. Charles
Coquerel, surgeon in the French Imperial navy, for the most exact
information concerning this dangerous Dipteron, and the revelation of
the dangers to which man is liable in certain parts of the globe. But
let us first describe the insect, which is very pretty and of
brilliant colours.
Fig. 52, taken from M. Charles Coquerel's Memoir, represents the larva
and the perfect insect, as well as the horny mandibles with which the
larva is provided. It is rather more than the third of an inch in
length, the head is large, downy, and of a golden yellow. The thorax
is dark blue and very brilliant, with reflections of purple, as is
also the abdomen. The wings are transparent, and have rather the
appearance of being smoked; their margins, as well as the feet, are
black.
This beautiful insect is an assassin. M. Coquerel has informed us that
it sometimes occasions the death of those wretched convicts whom human
justice has transported to the distant penitentiary of Cayenne.
When one of these degraded beings, who live in a state of sordid
filth, goes to sleep, a prey to intoxication, it happens sometimes
that this fly gets into his mouth and nostrils; it lays its eggs
there, and when they are changed into larvæ, the death of the victim
generally follows.[17]
[17] "The majority of convicts attacked by the _Lucilia
hominivorax_," says M. F. Bouyer, captain of the frigate, in
"Un Voyage à la Guyane Française," "have succumbed, despite the
assistance of science. Cures have been the exception: in a
dozen cases three or four are reported."--_Tour du Monde, 1866,
1er Semestre_, p. 318.
These larvæ are of an opaque white colour, a little over half an inch
in length, and have eleven segments. They are lodged in the interior
of the nasal orifices and the frontal sinuses, and their mouths are
armed with two very sharp horny mandibles. They have been known to
reach the ball of the eye, and to gangrene the eyelids. They enter the
mouth, corrode and devour the gums and the entrance of the throat, so
as to transform those parts into a mass of putrid flesh, a heap of
corruption.
Let us turn away from this horrible description, and observe that this
hominivorous fly is not, properly speaking, a parasite of man, as it
only attacks him accidentally, as it would attack any animal that was
in a daily state of uncleanliness.
In many works on medicine may be found mentioned a circumstance which
occurred twenty years ago, at the surgery of M. J. Cloquet. The story
is perhaps not very agreeable, but is so interesting as regards the
subject with which we are occupied, that we think it ought to be
repeated here. One day a poor wretch, half dead, was brought to the
Hôtel-Dieu. He was a beggar, who, having some tainted meat in his
wallet, had gone to sleep in the sun under a tree. He must have slept
long, as the flies had time enough to deposit their eggs on the
tainted meat, and the larvæ time enough to be hatched, and to devour
the beggar's meat. It seems that the larvæ enjoyed the repast, for
they passed from the dead meat to the living flesh, and after
devouring the meat they commenced to eat the owner. Awoke by the
pain, the beggar was taken to the Hôtel-Dieu, where he expired.
Who would suppose that one of the causes which render the centre of
Africa difficult to be explored is a fly not larger than the
house-fly? The Tsetse fly (Fig. 53) is of brown colour, with a few
transverse yellow stripes across the abdomen, and with wings longer
than its body. It is not dangerous to man, to any wild animals, or to
the pig, the mule, the ass, or the goat. But it stings mortally the
ox, the horse, the sheep, and the dog, and renders the countries of
Central Africa uninhabitable for those valuable animals. It seems to
possess very sharp sight. "It darts from the top of a bush as quick as
an arrow on the object it wishes to attack," writes a traveller, M. de
Castelnau.
[Illustration: Fig. 53.--The Tsetse Fly (_Glossina morsitans_).]
Mr. Chapman, one of the travellers who have advanced the farthest into
the middle of Southern Africa, relates that he covered his body with
the greatest care to avoid the bites of this nimble enemy; but if a
thorn happened to make a nearly imperceptible hole in his clothing, he
often saw the Tsetse, who appeared to know that it could not penetrate
the cloth, dart forward and bite him on the uncovered part. The
sucker of blood secretes--in a gland placed at the base of his
trunk--so subtle a poison, that three or four flies are sufficient to
kill an ox.
The _Glossina morsitans_ abounds on the banks of the African river,
the Zambesi, frequenting the bushes and reeds that border it. It
likes, indeed, all aquatic situations. The African cattle recognise at
great distances the buzzing of this sanguinary enemy, and this fatal
sound causes them to feel the greatest fear.
Livingstone, the celebrated traveller, in crossing those regions of
Africa that are watered by the Zambesi, lost forty-three magnificent
oxen by the bites of the Tsetse fly, notwithstanding that they were
carefully watched, and had been very little bitten.
"A most remarkable feature in the bite of the Tsetse is its perfect
harmlessness in man and wild animals, and even calves so long as they
continue to suck the cows. We never experienced the slightest injury
from them ourselves personally, although we lived two months in their
habitat, which was in this case as sharply defined as in many others,
for the south bank of the Chobe was infested by them, and the northern
bank, where our cattle were placed, only fifty yards distant,
contained not a single specimen. This was the more remarkable, as we
often saw natives carrying over raw meat to the opposite bank with
many Tsetses settled on it.
"The poison does not seem to be injected by a sting, or by ova placed
beneath the skin, for, when one is allowed to feed freely on the hand,
it is seen to insert the middle prong of three portions, into which
the proboscis divides, somewhat deeply, into the true skin. It then
draws it out a little way, and it assumes a crimson colour, as the
mandibles come into brisk operation. The previously-shrunken belly
swells out, and, if left undisturbed, the fly quietly departs when it
is full. A slight itching irritation follows, but not more than in the
bite of the mosquito. In the ox this same bite produces no more
immediate effects than in man. It does not startle him, as the gad-fly
does; but a few days afterwards the following symptoms supervene: the
eyes and nose begin to run, the coat stares as if the animal were
cold, a swelling appears under the jaw, and sometimes on the navel;
and, though the animal continues to graze, emaciation commences,
accompanied with a peculiar flaccidity of the muscles, and this
proceeds unchecked until, perhaps months afterwards, purging comes on,
and the animal, no longer able to graze, perishes in the state of
extreme exhaustion. Those which are in good condition often perish,
soon after the bite is inflicted, with staggering and blindness, as if
the brain were affected by it. Sudden changes of temperature produced
by falls of rain seem to hasten the progress of the complaint; but in
general the emaciation goes on uninterruptedly for months, and, do
what we will, the poor animals perish miserably.
"When opened, the cellular tissue on the surface of the body beneath
the skin is seen to be injected with air, as if a quantity of soap
bubbles were scattered over it, or a dishonest awkward butcher had
been trying to make it look fat. The fat is of a greenish-yellow
colour, and of an oily consistence. All the muscles are flabby, and
the heart often so soft that the fingers may be made to meet through
it. The lungs and liver partake of the disease. The stomach and bowels
are pale and empty, and the gall-bladder is distended with bile. These
symptoms seem to indicate, what is probably the case, a poison in the
blood; the germ of which enters when the proboscis is inserted to draw
blood. The poison-germ contained in a bulb at the root of the
proboscis, seems capable, although very minute in quantity, of
reproducing itself. The blood after death by Tsetse is very small in
quantity, and scarcely stains the hands in dissection....
"The mule, ass, and goat enjoy the same immunity from the Tsetse as
man and game. Many large tribes on the Zambesi can keep no domestic
animals except the goat, in consequence of the scourge existing in
their country. Our children were frequently bitten, yet suffered no
harm; and we saw around us numbers of zebras, buffaloes, pigs, pallahs
and other antelopes, feeding quietly in the very habitat of the
Tsetse, yet as undisturbed by its bite as oxen are when they first
receive the fatal poison. There is not so much difference in the
natures of the horse and zebra, the buffalo and ox, the sheep and the
antelope, as to afford any satisfactory explanation of the phenomenon.
Is a man not as much a domestic animal as a dog?
"The curious feature in the case, that dogs perish though fed on milk,
whereas the calves escape so long as they continue sucking, made us
imagine that the mischief might be produced by some plant in the
locality, and not by Tsetse; but Major Vardon, of the Madras army,
settled that point by riding a horse up to a small hill infested by
the insect, without allowing him time to graze, and though he only
remained long enough to take a view of the country and catch some
specimens of Tsetse on the animal, in ten days afterwards the horse
was dead."[18]
[18] "Missionary Travels and Researches in South Africa," by
David Livingstone, LL.D., D.C.L. P. 81, _et seq._ London, John
Murray, 1857. (The extract in the original of this work is from
a French translation: "Explorations dans l'Intérieur de
l'Afrique australe, et voyages à travers le continent
Sainte-Paul de Loanda à l'Embouchure du Zambèze, de 1840 à
1846, traduit de l'Anglais." Pages 93-95. 8vo. Paris,
1859.--ED.)
The inhabitants of the Zambesi can, therefore, have no domestic animal
but the goat. When herds of cattle driven by travellers or dealers are
obliged to cross these regions, they only move them during the bright
nights of the cool season, and are careful to smear them with dung
mixed with milk; the Tsetse fly having an intense antipathy to the
dung of animals, besides being in this season rendered dormant by the
lowness of the temperature. It is only by such precautions that they
are able to get through this dangerous stage of their journey.
The large blue Meat-fly, the familiar representative of the genus
_Calliphora_, is known to all by its brilliant blue and white
reflecting abdomen. This fly, which is common everywhere, is the
_Calliphora vomitoria_ on which Réaumur has made many beautiful
observations, which we will make known to our readers.
[Illustration: Fig. 54.--Eggs of the Meat-fly (_Calliphora vomitoria_).]
If we shut up a blue meat-fly in a glass vase, as Réaumur did, and
place near the insect a piece of fresh meat, before half a day is
passed, the fly will have deposited its eggs thereon one after the
other, in irregular heaps, of various sizes. The whole of these heaps
consist of about two hundred eggs, which are of an iridescent white
colour, and four or five times as long as they are broad. In less than
twenty-four hours after the egg is laid the larvæ is hatched. It is no
sooner born than it thinks of feeding, and buries itself in the meat
with the aid of the hooks and lancets with which it is provided.
These worms do not appear to discharge any solid excrement, but they
produce a sticky liquid, which keeps the meat in a moist state and
hastens its putrefaction. The larvæ eat voraciously and continually;
so much so, that in four or five days they arrive at their full
growth. They then take no more nourishment until they are transformed
into flies. They are now about to assume the pupa state. In this
condition it is no longer necessary for them to remain on the tainted
meat, which has been alike their cradle and their larder, and where
until now they were so well off. They therefore leave it and seek a
retreat under ground.
The larva then assumes a globular form and reddish colour, loses all
motion, and cannot any longer either lengthen or shorten, or dilate or
contract itself. Life seems to have left it. "It would be considered a
miracle," says Réaumur, "if we were told there was any kind of
quadruped of the size of a bear, or of an ox, which at a certain time
of the year, the beginning of winter for instance, disengages itself
completely from its skin, of which it makes a box of an oval form;
that it shuts itself up in this box; that it knows how to close it in
every part, and besides that it knows how to strengthen it in such a
manner as to preserve itself from the effects of the air and the
attacks of other animals. This prodigy is presented to us, on a small
scale, in the metamorphosis of our larva. It casts its skin to make
itself a strong and well-closed dwelling."
If one opens these cocoons only twenty-four hours after the
metamorphoses of the worms, no vestige of those parts appertaining to
a pupa is to be found. But four or five days afterwards, the cocoon is
occupied by a white pupa, provided with all the parts of a fly. The
legs and wings, although enclosed in sheaths, are very distinct; these
sheaths being so thin that they do not conceal them. The trunk of the
fly rests on the thorax; one can discern its lips, and the case which
encloses the lancet. The head is large and well formed, its large,
compound eyes being very distinct. The wings appear still unformed,
because they are folded, and, as it were, packed up. It is a fly, but
an immovable and inanimate fly; it is like a mummy enveloped in its
cloths.
Nevertheless, it is intended this mummy should awake, and when the
time comes it will be strong and vigorous. Indeed, it has need of
strength and vigour to accomplish the important work of its life.
Although its coverings are thin, it is a considerable work for the
insect to emerge, for each of its exterior parts is enclosed in them
as in a case, much the same as a glove fits tightly to all the fingers
of the hand. But that for which the most strength is necessary is the
operation of forming the opening of the cocoon, in which as a mummy it
is so tightly enclosed.
The fly always comes out at the same end of the cocoon, that is, at
the end where its head is placed, and also where the head of the larva
previously was. This end is composed of two parts--of two half cups
placed one against the other. These can be detached from each other
and from the rest of the cocoon. It is sufficient for the fly that one
can be detached, and in order to effect this, it employs a most
astonishing means. It expands and contracts its head alternately, as
if by dilatation; and thus pushes the two half cups away from the end
of the cocoon. This is not long able to resist the battering of the
fly's head, and the insect at length comes out triumphant. This fly,
which should be blue, is then grey; it, however, comes quickly to
perfection, at the end of three hours attaining its ultimate colour;
and in a very short space of time every part of the animal becomes of
that firmness and consistency which characterises them. At the same
time, the wings, which at the moment it came into the world were only
stumps, extend and unfold themselves by degrees. The meat-fly is
represented below (Fig. 55).
One of the features in the formation of this fly which most attracted
the attention of Réaumur, and which is likely to excite the curiosity
of all those who take an interest in insects, is the composition of
its trunk. We will, therefore, with that illustrious observer, take a
glimpse at the remarkable and complicated apparatus by the aid of
which the fly can suck up liquids, and can even taste solid and
crystalline substances, such as sugar.
[Illustration: Fig. 55.--Blue-bottle fly (_Calliphora vomitoria_),
magnified.]
It is no difficult matter to make a fly show its trunk extended to its
full extent. One has only to press between the finger and thumb either
the two sides of the upper and under part of the thorax. It is thus
forced at once to put out its tongue.
[Illustration: Fig. 56.--Trunk of the Meat-fly.]
[Illustration: Fig. 57.--Conical part of the trunk.]
The trunk appears to be composed of two parts joined together, and
forming a more or less obtuse angle (Fig. 56). The first portion of
the trunk, that which joins the head, is perfectly membranous and in
the form of a funnel. We will call it the conical part, and show it
separately (Fig. 57). The second portion terminates in a thick mass,
in part cartilaginous or scaly, and of a shiny brown colour. Above
the conical portion are two oblong antennæ, without joints, of
chestnut colour, and furnished with hairs.
On ceasing to press the thorax, the membranous conical portion may be
seen to draw itself back within its sheath (Fig. 58). The second
portion is at the same time drawn into the cavity, but it raises
itself by forming a more and more acute angle, so that when it reaches
the opening of the cell it is parallel with, and its length is equal
to that of the cell, which is quite large enough to receive it. The
base lengthens and flattens a little, and conceals the trunk.
[Illustration: Fig. 58.--Retractile proboscis of Blue-bottle fly.]
[Illustration: Fig. 59.--Extremity on the proboscis of a fly.]
Let us cause the trunk to extend itself a second time, in order to
observe its tip minutely. Here the opening is placed, which may be
looked upon as the mouth of the insect, and is provided with two large
thick lips (Fig. 59). These lips form a disc, perpendicular to the
axis of the trunk; the disc is oval, and is divided into two equal and
similar parts by a slit. The lips have each a considerable number of
parallel channels situated perpendicularly to the slit. These channels
are formed by a succession of vessels placed near each other. On
pressing the trunk we see that these vessels are distended by a
liquid. Réaumur, from whom we borrow these details, discovered a few
of the uses to which this trunk is applied. He covered the interior of
a transparent glass vase with a light coat of thick syrup. He then put
in some flies, when it was easy to see some of them proceed to fix
themselves to the sides of the vase, and regale themselves on the
sugary liquid, of which they are very fond. He observed them
carefully, and in his admirable work he recommends those who are
curious to try the experiment, with which, like himself, they will
certainly be satisfied.
While the body of the trunk is stationary its end is much agitated. It
may be seen to move in different ways, and with an astonishing
quickness; the lips acting in a hundred different ways, and always
with great rapidity. The small diameter of the disc which they form
lengthens and shortens alternately; the angle formed by the two lips
varies every instant; they become successively flat and convex, either
entirely or partly. All these movements, Réaumur remarks, give a high
idea of the organisation of the part which performs them.
The object of all these movements is to draw the syrup into the
interior of the trunk. If we observe the lips (Fig. 60) attentively,
it will easily be seen that they touch each other about the centre of
the disc, and leave two openings, one in front, the other at the back.
The one in front is, one may say, the mouth of the fly, as it is to
this opening that the liquid is brought, which is intended to be and
is soon introduced into the trunk. Without occupying ourselves for the
present with the channel through which it rises, we may first ask,
whatever that channel may be, what is the power that forces the liquid
into it?
[Illustration: Fig. 60.--Lips of the proboscis of a fly.]
It is nearly certain that suction is the principal cause of the liquid
flowing up the trunk. It would thus be a sort of pump, into which the
liquid is forced by the pressure of the external air. The fly exhausts
the air from the tube of its trunk, and the drop of liquid which is at
the opening penetrates and goes up this channel through the influence
of the atmospheric pressure. To this physical phenomenon must be added
the numerous and multiplied movements which take place in the trunk,
and which are intended to cause sufficient pressure to drive the
liquor which is introduced into the channel upwards.
Réaumur wished to know how it was that very thick syrups, and even
solid sugar, can be sucked up by the soft trunk of the fly. What he
saw is wonderful. If a fly meets with too thick a syrup, it can render
it sufficiently liquid; if the sugar is too hard, it can dissolve
small portions of it. In fact, there exists in its body a supply of
liquid, of which it discharges a drop from the end of its trunk at
will, and lets this fall on the sugar which it wishes to dissolve, or
on the syrup it wishes to dilute. A fly, when held between the
fingers, often shows at the end of its trunk a drop, very fluid and
transparent, of this liquid. "The water poured on the syrup," says
Réaumur, "would not always insinuate itself sufficiently quick into
every part of it; the movement of the fly's lips hastens the
operation; the lips turn over, work, and knead it, so that the water
can quickly penetrate it, in the same way as one handles and kneads
with one's hands a hard paste which it is wished to soften, by causing
the water by which it is covered to mix with it. This, again, is the
same means the fly employs with sugar. When the trunk is forced to
act upon a grain of irregular and rugged form, on which it cannot
easily fasten, its end distorts itself to seize and hold it. It is
sometimes very amusing to see how the fly turns over the grain of
sugar in different ways; it appears to play with it as a monkey would
with an apple. It is, however, only that it may hold it well in order
to moisten it more successfully, and afterwards to pump up the water
which has partly dissolved it."
Réaumur often observed a drop of water at the end of the trunks of
flies which were perfectly surfeited with food. This drop ascended the
trunk, then re-descended to the end, and this many times in
succession. It appeared to him that it was necessary for these
insects, as for many quadrupeds, to chew the cud, as it were; that, in
order the better to digest the liquid they had passed into their
stomachs, they were obliged to bring it back into the trunk that it
might return again better prepared.
In order to assure himself directly of the reality of his supposition,
Réaumur tested the water which a fly, that he says "had got drunk on
sugar," had brought back to the end of its trunk; he found this to be
sugar and water. Also, having given a fly currant-jelly, he observed,
after it had sufficiently gorged itself, several drops of red liquid
in its trunk, and having tasted it, found it had the flavour which,
from its appearance, he guessed it would have.
The illustrious observer, who had already made all these discoveries
on the formation and functions of the trunks of insects, often
reflected on the fact that the liquors of which flies are most fond
are enclosed under the skin of certain fruits, such as pears, plums,
grapes, &c., or even under the skin of some animals of which they suck
the blood. In order that the trunk of a fly may act under such
circumstances, it is necessary for it to pierce and open the skin. If
this is the case, flies ought to be possessed of a lancet. He looked a
long time for this lancet, and at last found it. It is situated on the
upper side of the part of the trunk which is terminated by the lips;
it is placed in a fleshy groove, and is enclosed in a case. It has a
very fine point, and is of light colour (Fig. 61). The point is
situated in the opening which is to be seen between the lips of the
trunk, at its anterior end, through which liquids may pass. That is
the only opening of the lips; and the sucker which takes up the liquid
is the same part which we just now called the case of the lancet.
Réaumur is so interesting an author that it is difficult to cease
quoting him; but we must continue our review of the principal kinds of
Diptera.
The genus _Musca_ (fly), in which Linnæus comprised the immense series
of Diptera, with the exception of the _Tipulidæ_, the _Tabanidæ_, the
_Asilidæ_, the _Bombylidæ_, and the _Empidæ_, is now reduced to the
House Fly and a few resembling it. The habits of these troublesome
companions are in conformity with the two great principles of animal
life, that is, eating and propagating their species.
Flies feed principally on fluids which exude from the bodies of
animals; that is, sweat, saliva, and other secretions. They also seek
vegetable juices; and they may be seen in our houses to feed eagerly
on fruits and sweet substances.
[Illustration: Fig. 61.--Lancet of the Meat Fly.]
[Illustration: Fig. 62.--House Fly (_Musca domestica_).]
The common flies deposit their eggs on vegetables, and particularly on
fungi in a state of decomposition, on dung-heaps, cow dung, &c. They
are essentially parasites, settling on both man and beast, to suck up
the fluid substances which are diffused over the surface of their
bodies. In our dwellings they eat anything that will serve to nourish
them. Generation succeeds generation with the greatest rapidity.
The House Fly (_Musca domestica_, Fig. 62) is about three lines in
length, ash coloured, with the face black, the sides of the head
yellow, and the forehead yellow with black stripes; the thorax is
marked with black lines; the abdomen is pale underneath, and a
transparent yellow at the sides, in the males, and is speckled with
black. The feet are black; the wings transparent, and yellowish at the
base. This species is extremely plentiful throughout the whole of
Europe. Every one knows how annoying it is towards the end of the
summer, and especially so in the South of France during the hot
season.
The Ox Fly (_Musca bovina_), a near relation of the house fly, is also
very common. It settles on the nostrils, the eyes, and the wounds of
animals.
The Executioner Fly (_Musca carnifex_), which is not rare in France,
also attacks oxen. It is of a dark metallic green colour with a
slight ash-coloured down. Its forehead is silvery at the front and
sides; the abdomen is edged with black; the wings hyaline, and yellow
at the base.
_Section of the Anthomyides._--The section of _Anthomyides_ comprises
insects which appear to be _Creophili_ whose organisation has become
weakened by almost insensible degrees. Their colours vary very
much--black, grey, and iron-colour are everlastingly shaded and
blended together. To that may be added reflections which are above the
ground colour, and which change the hues of the little animal
according to the incidence of the rays of light. The _Anthomyides_
resemble the genus _Musca_ very closely in their habits as well as in
their organisation.
In this group of Diptera we will first say a few words about the
_Anthomiæ_. These flies are to be found in most gardens, and on all
flowers, particularly on the heads of Compositæ and Umbelliferæ. They
often unite in numerous bands in the air, and indulge in the joyous
dances to which love invites them. The females deposit their eggs in
the ground, and their larvæ are there quickly developed. The latter
suspend themselves to certain bodies, the same as some lepidopterous
chrysalides, in order to transform themselves into pupæ.
The _Anthomyia pluvialis_ (Fig. 63) is from two to four lines in
length, and of a whitish ash-colour. Its wings are hyaline, the thorax
has five black spots, and the abdomen three rows of similar spots.
[Illustration: Fig. 63.--Anthomyia pluvialis.]
We will stop a moment with the _Pegomyiæ_, which are very interesting
in the larva state, and which excited the interest and sagacity of
Réaumur.
The cradle of these Diptera is the interior of leaves. They work as
the miners of the vegetable world, in the parenchyma or cellular
tissue of the leaf, between the two epidermal membranes. The henbane,
the sorrel, and the thistle, especially nourish them. If one holds a
leaf in which one of these miners has established itself against the
light, one sees the workman boring the vegetable membrane. Its head is
armed with a hook, formed of two horny pieces, and with this hook it
digs into the parenchyma of the leaf. The effect of this digging is
visible, as those places become by degrees transparent. Each blow
detaches a small portion of the substance of the leaf. It is thus that
these miners hollow out galleries for themselves, in which they find
shelter, food, and security. Some are changed into pupæ in the gallery
which they have hollowed out, others go out of the leaves when they
are near their final transformation.
_Section of Acalyptera._--The _Acalyptera_, which are the last of the
great tribe of _Muscidæ_, comprehend the greater number of these
insects. Their constitution appears to be peculiar and slow. They live
principally in the thickest part of woods, on grasses, and aquatic
plants. Fearing the lustre and warmth of the sun, they never draw the
nectar from flowers. Their flight is feeble, and they never indulge in
those joyous ethereal dances which we have mentioned when speaking of
the preceding groups. Their life is generally melancholy, obscure, and
hidden. Some of them seek decomposed animal and vegetable substances,
others living vegetables.
We shall only be able in this immense group of _Muscidæ_ to mention a
few types which are interesting from various reasons, such as the
_Helomyzæ_, the _Scatophagæ_, the _Ortalides_, the _Daci_, and the
_Thyreophoræ_.
[Illustration: Fig. 64.--A species of Helomyza.]
The _Helomyzæ_ (Fig. 64) live in the woods. Their larvæ are developed
in the interior of fungi. Réaumur studied the larvæ of the Truffle
Helomyza. The head of this fly is ferruginous, its thorax is of a
brownish grey, its shoulders of a brownish yellow, its wings brownish,
the abdomen yellow and brown, and the feet red. The larvæ of these
insects commit depredations for which gourmands will never forgive
them, destroying, as they do, their truffles. When one presses between
one's fingers a truffle that is in a too advanced state, one feels
certain soft parts, which yield under pressure. On opening the
truffle, the larvæ of the insect of which we are speaking will be
found inside. These larvæ are white and very transparent. Their mouth
is armed with two black hooks, by means of which they dig into the
truffle in the same way as other larvæ dig into meat. The excretions
of these little parasites cause the truffle to become decomposed and
rotten. In a few days the larvæ become full-grown. They then leave
their abode and go into the ground, there to change into pupæ.
The _Ortalidæ_ form a tribe which is remarkable for the upright
carriage of the wings, which are generally speckled, by the vibratory
movement of these organs, and especially for the cradle chosen by them
for their progeny in fruits and grains. Nature seems to have assigned
to each species its own particular vegetable.
We will only mention here the Cherry-tree _Ortalis_, whose larva lives
on the pulp of that fruit. This fly is about a line and a half long.
It is of rather a metallic black colour, its head light yellow, the
edges of its eyes white, and the tarsi red. The wings have four broad
black stripes.
[Illustration: Fig. 65.--Dacus oleæ.]
The Olive Dacus (_Dacus oleæ_, Fig. 65) is a little fly, about half
the size of the house fly, of ashy grey colour on the back, its head
orange-yellow, its eyes green, and its forehead yellow, marked with
two large black spots. The thorax is adorned with four lightish yellow
spots, and its hind part, as well as its antennæ and wings, are of the
same colour. The wings are transparent, reflecting green, gold, pink,
and blue, according as the rays of light fall upon them, and are
remarkable for having a small black spot at their extremity. The
abdomen is of a fawn colour or orange-yellow, spotted with black on
each side. This fly performs sudden and jerking movements; it keeps
its wings extended, and rather jumps than flies. It is a destructive
insect, a perfect scourge, which causes every two or three years a
loss of five or six millions of francs to French agriculture.
M. Guérin-Méneville has made some valuable observations on the Olive
Dacus, and at the request of the Imperial Society of Agriculture of
Paris, has indicated the way to preserve the olive from these ruinous
larvæ, which generally destroy two crops out of three. We will borrow
the following details from this learned entomologist: "At the time
when the olives are formed the Dacus proceeds to place an egg under
the skin of each of the fruits. By means of a little horny instrument,
with which the female is provided, and which contains a small lancet,
she pierces the skin of the olive; she moves her wings and lays her
egg. She afterwards cleans and rests herself, by passing her feet over
her head, wings, and other parts of her body. She then flies away, and
seeks another olive, to deposit in it another egg; she repeats this
operation until she has placed on as many olives the three or four
hundred eggs which she bears."
[Illustration: Fig. 66.--Olives attacked by Dacus oleæ.]
Fig. 66, taken from the Memoir published by M. Guérin-Méneville, in
the "Revue Nouvelle" of the 15th July, 1847, shows the Dacus laying
its eggs on the olive, and the larvæ that are already hatched in
another of the same fruit. The larvæ which succeed these eggs (Fig.
67) are whitish, soft, and without limbs. They pass fifteen or sixteen
days in boring a gallery in the pulp of the olive, at first
vertically, until they reach the stone, then on one side, and along
the side of the stone. When they have reached the term of their
development, they approach the surface, enlarging the first channel
and leaving between it and the exterior air only a thin pellicle, in
the middle of which may be perceived the first small opening by which
the mother had introduced her egg in the commencement.
[Illustration: Fig. 67.--Larvæ of Dacus oleæ (magnified and natural
size).]
[Illustration: Fig. 68.--Gallery formed by larva of Dacus oleæ.]
Fig. 68, copied from a drawing in the Memoirs of M. Guérin-Méneville,
shows the gallery bored round the olive by the larva of the Dacus. The
larva thus prepares an easy issue for the perfect insect. Its skin
then contracts, its body diminishes in length, and is transformed into
an oval cocoon, which soon gets brown, and is the chrysalis of the
insect. At the side of the head it shows a curved line, a thin suture
which marks a sort of cap or door, which, at the time of its hatching,
the insect will be easily able to force open with its head. The fly is
hatched twelve days after its metamorphosis from the larva to the
pupa. It has thus taken the Dacus twenty-seven to twenty-eight days to
arrive at this state, from the time the egg was laid; besides which,
this species, in the warm climates of Provence and Italy, can
reproduce itself several times from the beginning of July, the period
at which the first flies begin to lay, till the end of autumn.
In order to save a considerable portion of the olive crop of these
countries, M. Guérin-Méneville has advised hastening the harvest
sufficiently for all the olives to be pressed at a time when the larvæ
of the last generation, which would be preserved in the olives that
are left, or in the earth, according to the climate, are still in the
fruit. If a first operation were not sufficient to destroy them all,
it should be repeated the following year. The sacrifice entailed by
this practice would be amply compensated by a succession of good crops
and the certainty of a sure and permanent profit. In fact, by an early
gathering at least half a crop of oil is still obtained; whereas, by
waiting for the usual period of gathering the olives, sufficient time
is left for the larvæ of the Dacus to devour their parenchyma, which
deprives them of the little oil that they might have yielded if their
destruction had been accomplished earlier. This early gathering has
the advantage of causing the destruction of a great number of larvæ,
which will be so much towards diminishing the means of reproduction of
the fly.
III.
HEMIPTERA.
The Hemiptera are particularly distinguished from other kinds of
insects by the form of their mouth, which consists of a beak, more or
less long, composed of six parts: that is, of a lower lip, or sheath;
four internal threads, representing the mandibles and jaws of the
grinding insects, and which are the perforating parts of the beaks;
and, lastly, of the upper lip or labrum. Owing to this apparatus,
these insects are essentially sucking ones, and chiefly nourish
themselves with the juices of vegetables, which they draw up with
their beak. The wings of the Hemiptera are usually four in number; in
some species they are membranous and similar to each other, and in
others the upper are of rather harder consistency than the lower ones.
In general, the former are quite different from the lower wings, and
are only membranous at the tip, whereas the other part is thick,
tough, and coriaceous.
The Hemiptera are divided into two very distinct sections. The one is
composed of insects whose beak grows from the forehead or upper part
of the head, and whose anterior wings are half coriaceous and half
membranous, having the base of a different texture from the extremity:
these are the Heteroptera ([Greek: heteros], different; [Greek:
pteron], wing). The other section is composed of those whose beak
grows from the lower part of the head, and whose anterior wings are
always of the same consistency throughout: these are the Homoptera
([Greek: homos], the same; [Greek: pteron], wing). We are about to
give the history of these two sub-orders.
HETEROPTERA.
The insects formerly known by the general name of Bugs have been
divided by Latreille into two large families, containing: the one the
_Geocorisæ_,[19] or Land Bugs; the other the _Hydrocorisæ_,[20] or
Water Bugs.
[19] From [Greek: gê], the earth, and [Greek: koris], a bug.
[20] From [Greek: hydôr], water, and [Greek: koris], a bug.
The land bugs consist of a great number of kinds, which, for the
most part, are of little interest. We will only mention here the
_Peniatomidæ_, commonly known as Wood Bugs; the _Lygæi_, Bugs,
properly so called; the _Reduvii_, and the _Hydrometræ_.
The _Pentatomidæ_, which comprise many genera, include the wood bugs
of most authors. They are to be found on plants and trees. They fly
quickly, but only for a short time.
The Ornamented Pentatoma (_Strachia_ [_Pentatoma_] _ornata_), known
as the Red Cabbage Bug, is very commonly found on the cabbage, and
on most of the cruciferous plants. It is variegated with red and
black, and its colours are subject to numerous variations. The Grey
Pentatoma (_Raphigaster griseus_), Fig. 69, is common throughout the
whole of Europe. In autumn these bugs are frequently to be found on
raspberries, to which they impart their disagreeable smell. They are
also to be found in quantities on the mullein, when that plant is in
flower. The upper parts of the head are of a greyish brown, and are
sometimes slightly purple. The coriaceous part of the hemelytra
is of a purple tint, but the membranous part is brown. All these
parts are covered with black spots, which are only to be seen with
a magnifying-glass. The wings are blackish. The under part of the
whole body and the feet are of a light and rather yellowish grey, with
a considerable number of small black spots. The abdomen is black above;
and it is bordered with alternate black and white spots.
[Illustration: Fig. 69.--Grey Pentatoma (_Raphigaster griseus_).]
We have repeated here the description given of this bug by the
illustrious Swedish naturalist, De Geer, because our young readers
have most likely met with this insect, or will do so some day when
gathering raspberries.
The Grey Pentatoma, marked with black, yellow, and red, is to be found
throughout the whole of Europe in cultivated fields and gardens,
sometimes also on the trunks of large trees, especially elms. This
species, in common with the greater part of those which compose the
group we are describing, emits a smell when irritated or menaced by
some danger. At other times no odour will be noticed. Let us hear what
M. Léon Dufour says on this subject.
"Seize the Pentatoma with a pair of pincers and plunge it into a glass
of clear water; look through a magnifying-glass, and you will see
innumerable small globules arising from its body, which, bursting on
the surface of the water, exhale that odour which is so disagreeable.
This vapour, which is essentially acrid, if it happens to touch the
eyes, causes a considerable amount of irritation. If one of these
insects is held between the fingers, so as not to stop up the
odoriferous orifices, and to cause this vapour to touch a part of the
skin, a spot, either brown or livid, will ensue on that part, which
lotions, though repeatedly applied, will at first fail to remove, and
which produces in the cutaneous tissue an alteration similar to that
which succeeds the application of mineral acids."
The disagreeable smell exhaled by different species of Pentatoma is
the result of a fluid secreted by a single pear-shaped gland, either
red or yellow, which occupies the centre of the thorax, and which
terminates between the hind legs.
With the _Syromastes_, which are bugs of this same section, the
secretion has, on the contrary, an agreeable smell, which reminds one
of that of apples. Many kinds of Pentatoma are destructive to
agriculture. Others, however, attack the destructive insects, and
ought therefore to be carefully spared. We will mention in this case
the Blue Pentatoma, which kills the _Altica_[21] of the vine.
[21] This species is _Lygænus militaris_.--ED.
There may be observed, at the foot and about the lower part of trees,
or at the base of walls exposed to the mid-day sun, groups of fifty or
sixty small insects pressed close to each other, and often one on the
top of the other, their heads in the direction of a centre point. They
are red, spotted with black. In the neighbourhood of Paris the
children call them "_Suisses_," probably on account of the red on
their bodies, that being the colour of the uniform of the Swiss troops
formerly in the service of France. In Burgundy the children call them
"_petits cochons rouges_." They will be found described in Geoffroy's
"Histoire des Insectes," under the name of the Red Garden Bug. At the
present day they are placed in the genus _Lygæus_.[22] When the bad
weather comes, these little "_Suisses_" take refuge under stones and
the bark of trees to pass the winter. During the whole of that season
they remain in a sort of torpid state. But in the first days of spring
they revive, and resume their ordinary habits. They suck the sap of
vegetables, piercing the capsules of divers kinds of mallows, and
always keeping in the sunshine.
[22] A genus of beetles.
The Bug, popularly so called, or Bed Bug (_Acanthia lectularia_, or
_Cimex lectularius_, Fig. 70), a most disagreeable and stinking
insect, abounds in dirty houses, principally in towns, and above all
in those of warm countries. It lives in beds, in wood-work, and
paper-hangings. There is no crack, however narrow it may be, into
which it is unable to slip. It is nocturnal, shunning the light.
"Nocturnum foetidum animal," says Linnæus. Its body is oval, about
the fifth of an inch in length, flat, soft, of a brown colour, and
covered with little hairs. Its head is provided with two hairy
antennæ, and two round black eyes, and has a short beak, curved
directly under its thorax, and lying in a shallow groove when the
animal is at rest. This beak, composed of three joints, contains four
thin, straight, and sharp hairs. The thorax is dilated at the sides.
The abdomen is very much developed, orbicular, composed of eight
segments, very much depressed, and easily crushed by the fingers. The
hemelytra are rudimentary. It has no membranous wings. The tarsi have
three articulations, of which the last is provided with two strong
hooks.
[Illustration: Fig. 70.--Bed Bug (_Acanthia lectularia_), magnified.]
[Illustration: Fig. 71.--Egg of Bug, magnified.]
"These animals," says Moquin-Tandon, in his "Zoologie Médicale," "do
not draw up the sanguineous fluid by suction, properly so-called, as
leeches do. The organisation of their buccal apparatus does not allow
of this. The hairs of the beak applied the one against the other
exercise a sort of alternate motion, which draws the blood up into the
oesophagus, very much in the same manner as water rises in a chain
pump. This rising is assisted by the viscous nature of the fluid, and
above all, by the globules it contains." The part of the skin which
the Bug has pierced, producing a painful sensation, is easily
recognised by a little reddish mark, presenting in its centre a dark
spot. Generally a little blister rises on the point pierced, and
sometimes, if the Bug-bites are numerous, these blisters become
confluent, and resemble a sort of eruption. These disgusting insects
lay, towards the month of May, oblong whitish eggs (Fig. 71), having a
small aperture, through which the larva comes out. The larva differs
from the insect in its perfect state, in its colour, which is pale or
yellowish. This insect exists in nearly the whole of Europe, although
it is rare or almost unknown in the northern parts. The towns of
central Europe are the most infested by this parasite, but those of
the north are not completely free from its presence. The Marquis de
Custine assures us that at St. Petersburg he found them numerous. It
is found also in Scotland; is very rare in the south of Europe; and
seldom seen in Italy, where it is, however, replaced by other insects
more dangerous or more annoying.
It has been said that the Bug was brought into Europe from America;
but Aristotle, Pliny, and Dioscorides mention its existence. It is
certain that it was unknown in England till the beginning of the
sixteenth century. A celebrated traveller, a Spanish naturalist,
Azara, has remarked that the Bug does not infest man in his savage
state, but only when congregated together in a state of civilisation,
and in houses, as in Europe. From this he concluded that the Bug was
not created till long after man, when, after many centuries had
elapsed since his appearance on the globe, men formed themselves into
societies, into republics, or little states.
The bug is not a gluttonous insect, always bloodthirsty; on the
contrary, its sobriety is remarkable. It is only after a prolonged
fast that it bites animals; and Audouin has stated that it can live a
year and even two years without food.
From time immemorial a number of different means have been employed
for destroying these insects; but in spite of all, nothing is more
difficult than to get rid of them from wood-work and paper-hangings,
when they have once infested them. In general, strong odours cause
their death. And so, to rid oneself of these disagreeable guests, it
has been recommended to use tobacco smoke, essence of turpentine, the
fumes of sulphur, &c. Mercurial ointment and corrosive sublimate are
also excellent means for their destruction; and for the same purpose
the merits of a plant belonging to the order Cruciferæ, _Lepidium
ruderale_, have been much vaunted; and more recently still, the root
of the Pyrethrum, a species of camomile, reduced to powder, and blown
into the furniture or wood-work. This powder is known and employed at
Paris under the name of "_poudre insecticide_."
There are two other kinds of bugs (_Acanthia_) which attack men. The
one is the _Acanthia ciliata_, which has been found in the houses of
Kazan, and which differs from the bed bug not only in its form, but
also in its habits. It does not live in companies, in the narrow
cracks of furniture, but moves about alone, at a slow pace, over walls
or the counterpanes of beds. Its beak is very long, and its bite is
very painful, and produces obstinate swellings.
The other species is the _Acanthia rotundata_, which is found in the
Island of La Réunion, and attacks men in the same way as does the
European bug. Two species of the same genus live as parasites on
swallows and domestic pigeons. There is another species, which is
peculiar to the bats of our climates.
The _Reduvius personatus_, called also Fly Bug, by Geoffroy, the old
historian of the insects of the environs of Paris, is common enough
in France. It keeps to the houses, and is found especially near ovens
and chimney-pieces. It is about three-quarters of an inch in length,
oblong, flat on its upper side, brownish, has horizontal hemelytra
crossed over each other, and very fully developed wings, which serve
for flight. Its head, narrow, supported by a well-defined neck, is
provided with two composite and two simple eyes. It requires, no
doubt, to see very clearly, as it flies by night. It should not be
caught without great caution. If you desire to examine it closely,
when, in the hottest part of the summer, it comes in the evening and
flutters round the lights, you must be careful how you seize it, for
it wounds. The wounds inflicted by it are very painful--more painful
than those of the bee--and they immediately cause a numbness.
As the _Reduvius_ kills different insects very rapidly, by piercing
them with its long beak, it is probable that it secretes some kind of
venom. But as yet the organ that produces this poison has not been
discovered. However that may be, its beak is curved, and about the
tenth of an inch long, the surface bristling with hairs. It is
composed of three joints, and contains four stiff, lanceolate, and
very pointed squamose hairs.
This insect often seeks its prey in places where spiders spin their
webs. When they walk on, or are caught in, the spiders' webs, the
spiders take care not to seize them, for they fear their beak. They
prudently allow them to struggle about the nets, where they very soon
die of hunger. The _Reduvius_ is often seen, either a prisoner or
dead, in the midst of a spider's web.
"This bug," says Charles de Geer, "has, in the pupal condition, or
before its wings are developed, an appearance altogether hideous and
revolting. One would take it, at the first glance, for one of the
ugliest of spiders. That which above all renders it so disagreeable to
the sight is that it is entirely covered, and, as it were, enveloped
with a greyish matter, which is nothing else but the dust which one
sees in the corners of badly-swept rooms, and which is generally mixed
with sand and particles of wool, or silk, or other similar matters
which come from furniture and clothes, rendering the legs of this
insect thick and deformed, and giving to its whole body a very
singular appearance."
What instincts! what habits! Under this borrowed costume, under this
cloak, which is no part of itself, the insect, as it were, masked, has
become twice its real size. What becomes of its disguise, and how does
it manage to walk? Of what use to it is this dirty and grotesque fancy
dress?
Let us listen to De Geer. "It walks as fast, when it likes, as other
bugs; but generally its walk is slow, and it moves with measured
steps. After having taken one step forward, it stops a while, and then
takes another, leaving, at each movement, the opposite leg in repose;
it goes on thus continually, step after step in succession, which
gives it the appearance of walking as if by jerks, and in measure. It
makes almost the same sort of movement with its antennæ, which it
moves also at intervals and by jerks. All these movements have a more
singular appearance than it is possible for us to describe."[23]
[23] "Mémoires pour servir à l'Histoire des Insectes." Tome
iii., p. 283. 4to. Stockholm, 1773.
By means of this disguise, it can approach little animals, which
become its prey, such as flies, spiders, bed bugs.
[Illustration: Fig. 72.--Pupa of Reduvius personatus, covered with its
cloak of dust (magnified).]
[Illustration: Fig. 73.--Pupa of Reduvius personatus, denuded of its
cloak of dust (magnified).]
To see what a curious appearance the _Reduvius_ presents, one should
take off its borrowed costume. Then you will observe an entirely
different animal, and one which has nothing repulsive about it. With
the exception of the hemelytra and wings, which it has not yet got,
all its parts have the form which they are to have later, after the
wings are developed.
Fig. 72 represents, from Charles de Geer's Memoir, the pupa of the
_Reduvius personatus_ covered with dust, and resembling a spider; Fig.
73 the same insect cleaned, freed from the cloak of dust which served
to disguise it.
The _Hydrometræ_ (from [Greek: hydôr], water, and [Greek: metrein], to
measure) have linear bodies. The head, which forms nearly the third
of the entire length, is furnished with two long antennæ, and armed
with a thin, hair-like beak. The legs are long, and of equal length.
The reader may have often seen the _Hydrometra stagnorum_ walking by
jerks on the surface of the water (Fig. 74). The body and legs are of
a ferruginous colour, the hemelytra a dull brown, and the wings
hyaline, or glassy, and slightly blackish. Geoffroy says that it
resembles a long needle, and calls it the Needle Bug.
[Illustration: Fig. 74.--Hydrometra stagnorum.]
The _Hydrocorisæ_, or Water Bugs, have the antennæ shorter than the
head, or scarcely attaining to its length, and inserted and hidden
under the eyes, which are in general of remarkable size. All these
Hemiptera are aquatic and carnivorous. We will mention the two
principal types, the _Nepæ_, or Water Scorpions, and the _Notonectæ_,
or Boatmen.
The _Nepa cinerea_ (Fig. 75), which Geoffroy calls the Oval-bodied
Water Scorpion, and which he also designates by the name of the Water
Spider, is very common in the stagnant waters of ponds and ditches.
Its body, oval, very flat, of an ashy colour, with red on the abdomen,
is four-fifths of an inch long. The hemelytra are horizontal,
coriaceous, and of a dirty grey colour. Its front legs, with short
haunches, and very broad thighs, are terminated by strong pincers,
which give to the insect a strong resemblance to the scorpion. It is
by folding back the leg and the tarsus under the thigh, that the
animal holds its prey, and sucks it with its rostrum or beak.
[Illustration: Fig. 75.--Nepa cinerea.]
This rostrum is composed of three joints, and contains four pointed
bristles. Two present on one side a sort of narrow sharp blade, and
have teeth towards their base. Of the two others, the one is a thin
smooth needle, the other is provided with hairs directed backwards and
forwards.
It is with this rostrum, which resembles a case of surgical
instruments, that the _Nepa_ pierces and sucks little aquatic insects,
not even sparing its own species. Its wound is painful to man, but not
in the least dangerous. With its four hind legs the _Nepa_ swims, but
at a very slow pace. It generally drags itself along the bottom of
the water, on the mud, and does not avoid the hand put out to seize
it. Its body is terminated by a tail, composed of two grooved threads,
which, when applied together, form a tube, capable of being moved from
side to side. Through this canal it breathes the outer air; it puts
the end of it out of the water, and the air enters it by inspiration.
Some very small hairs, with which the interiors of the grooves are
lined, interlace each other, and prevent the water from penetrating
into the canal. It is probable that this same canal serves also for
depositing the eggs. These last resemble small seeds, covered with
points, and are buried in the stalks of aquatic plants.
Next to the _Nepa_ comes the _Ranatra_, with a cylindrical, elongated,
linear body, with very long and very thin hind legs, and of which one
species, which Geoffroy calls the "aquatic scorpion with an elongated
body," is common everywhere in stagnant waters in spring. It is
brownish, carnivorous, and very voracious.
[Illustration: Fig. 76.--Corixa striata.]
We must now mention the genus _Corixa_, of which one species, the
_Corixa striata_, is very common. This insect walks badly and slowly
on land, but swims and cuts through the water with a prodigious
rapidity.
However, it is not to delay over this last species that we have here
mentioned the name of this genus. Some insects which belong to it, and
which are found in Mexico, deserve to be alluded to, on account of
certain peculiarities which their eggs present. A naturalist, M.
Virlet d'Aoust, has published the following details on this subject:--
"Thousands of small amphibious flies," he says, "flit about in the air
on the surface of lakes, and diving down into the water many feet, and
even many fathoms, go to the bottom to lay their eggs, and only emerge
from the water probably to die close by. We were fortunate enough to
be present at a great fishing or harvest of the eggs, which, under the
Mexican name of _hautle_ (_haoutle_), serve for food to the Indians,
who seem to be no less fond of them than the Chinese are of their
swallows' nests, which they resemble somewhat in taste; only the
_hautle_ is far from commanding such high prices as the Chinese pay
for their birds' nests, which for that reason are reserved entirely
for the tables of the rich; while, for a few small coins, we were
able to carry away with us about a bushel of the _hautle_, a portion
of which, at our request, Mme. B---- was kind enough to prepare for
us.
"They dress these in different ways, but generally make a sort of
cake, which is served up with a sauce, to which the Mexicans give a
zest, as they do indeed to all their dishes, by adding to it _chilié_,
which is composed of green pimento crushed. This is how the natives
proceed when they are fishing for _hautle_: they form with reeds bent
together a sort of fasces, which they place vertically in the lake at
some distance from the bank, and as these are bound together by one of
the reeds, the ends of which are so arranged as to form an indicating
buoy, it is easy to draw them out at will. Twelve to fifteen days
suffice for each reed in these fasces to be entirely covered with
eggs, which they thus fish up by millions. The former are then left to
dry in the sun, on a cloth, for an hour or more; the grains are then
easily detached. After this operation, they are replaced in the water
for the next hautle harvest."
M. Virlet had attributed to flies the eggs of which we have been
speaking. But in 1851 M. Guérin-Méneville having received, transmitted
to him by M. Ghiliani, eggs of which _hautle_ is made, and some of the
insects said to produce them, stated that the latter belonged to two
different species. The one had been known a long time since under the
name of _Corixa mercenaria_; M. Guérin-Méneville called the other
_Corixa femorata_.
The same entomologist discovered, among the eggs of these two species,
other eggs of a more considerable size, and which he attributed to a
new species of the genus _Notonecta_, about which we are now going to
say a few words.
The _Notonecta glauca_, which Geoffroy calls the Large Bug with Oars
("Grande punaise à avirons"), is very common in ditches, reservoirs,
and stagnant waters. Its body is oblong, narrow, contracted
posteriorly, convex above, flat below, having, at its sides and its
extremities, hairs which, when spread out, support the animal on the
water. Its head is large and of a slightly greenish grey, and has on
each of its sides a very large eye of a pale brown colour. Its thorax
is greyish, the hemelytra of a greenish grey, the membranous wings
white. Of its legs, the front four are short; but the hind legs,
almost twice as long, are furnished with long hairs, and resemble
oars. It is with the aid of these that the animal moves through the
water; and it does so in a singular manner, placing itself on its
back, and generally in an inclined position, as in Fig. 77.
When this insect, on the contrary, drags itself along on the mud, the
front legs are those which it employs, the hind legs being idle, and
merely drawn along behind it. It is generally towards the evening or
during the night that it comes out of the water, to walk and to fly,
if it wishes to pass from one marsh to another.
[Illustration: Fig. 77.--Notonecta glauca.]
This bloodthirsty insect lives entirely by rapine; it is one of the
most carnivorous of insects. Those which it attacks die very soon
after they have been hurt by it. De Geer thinks that the water bug
drops into the wound a poisonous humour. It seizes upon insects much
bigger, and apparently much stronger, than itself, and does not spare
its own species.
The instrument with which the _Notonecta_ attacks its prey is composed
of a very strong and very long conical beak, formed of four joints.
The sucker is composed of an upper piece, short and pointed, and of
four fine pointed hairs.
The female of the _Notonecta glauca_ lays a great number of eggs,
white, and of elongated shape, which it deposits on the stems and
leaves of aquatic plants. The eggs are hatched at the beginning of
spring, or in May, and the young ones at once begin to swim about like
their mother, on their backs, belly upwards. M. Léon Dufour says on
this subject:--
"A dorsal region, raised like a donkey's back, or like the rounded
keel of a boat, and covered with a velvety substance, which renders it
impermeable, numerous fine fringes which garnish either the hind legs,
or the borders of the abdomen and thorax, or lastly in a double row
form a crest or comb running down the surface of the belly, and which
spread themselves out or fold themselves in at the will of the insect,
just like fins, favour both this supine attitude and the accuracy of
the swimming movements of the _Notonectæ_. Since Nature--which seems
often to delight in producing extraordinary exceptions to her ordinary
rules, thus bearing witness to the immensity of her resources--had
condemned this animal to pass its life in an inverted position, it was
necessary, for the maintenance of its existence, that it should
provide it with an organisation in harmony with this attitude. It is
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