Animal Intelligence
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Title: Animal Intelligence
Author: George John Romanes
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*** START OF THE PROJECT GUTENBERG EBOOK ANIMAL INTELLIGENCE ***
THE INTERNATIONAL SCIENTIFIC SERIES.
VOLUME XLIV.
I HAVE recently learnt from the publishers of the 'International
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Necessarily, therefore, the material to be dealt with in his work will
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ANIMAL INTELLIGENCE.
BY
GEORGE J. ROMANES, M. A., LL. D., F. R. S.,
ZOOLOGICAL SECRETARY OF THE LINNEAN SOCIETY.
NEW YORK:
D. APPLETON AND COMPANY,
1, 3, AND 5 BOND STREET.
1884.
PREFACE.
WHEN I first began to collect materials for this work it was my
intention to divide the book into two parts. Of these I intended the
first to be concerned only with the facts of animal intelligence, while
the second was to have treated of these facts in their relation to the
theory of Descent. Finding, however, as I proceeded, that the material
was too considerable in amount to admit of being comprised within the
limits of a single volume, I have made arrangements with the publishers
of the 'International Scientific Series' to bring out the second
division of the work as a separate treatise, under the title 'Mental
Evolution.' This treatise I hope to get ready for press within a year or
two.
My object in the work as a whole is twofold. First, I have thought it
desirable that there should be something resembling a text-book of the
facts of Comparative Psychology, to which men of science, and also
metaphysicians, may turn whenever they may have occasion to acquaint
themselves with the particular level of intelligence to which this or
that species of animal attains. Hitherto the endeavour of assigning
these levels has been almost exclusively in the hands of popular
writers; and as these have, for the most part, merely strung together,
with discrimination more or less inadequate, innumerable anecdotes of
the display of animal intelligence, their books are valueless as works
of reference. So much, indeed, is this the case, that Comparative
Psychology has been virtually excluded from the hierarchy of the
sciences. If we except the methodical researches of a few distinguished
naturalists, it would appear that the phenomena of mind in animals,
having constituted so much and so long the theme of unscientific
authors, are now considered well-nigh unworthy of serious treatment by
scientific methods. But it is surely needless to point out that the
phenomena which constitute the subject-matter of Comparative Psychology,
even if we regard them merely as facts in Nature, have at least as great
a claim to accurate classification as those phenomena of structure which
constitute the subject-matter of Comparative Anatomy. Leaving aside,
therefore, the reflection that within the last twenty years the facts of
animal intelligence have suddenly acquired a new and profound
importance, from the proved probability of their genetic continuity with
those of human intelligence, it would remain true that their systematic
arrangement is a worthy object of scientific endeavour. This, then, has
been my first object, which, otherwise stated, amounts merely to passing
the animal kingdom in review in order to give a trustworthy account of
the grade of psychological development which is presented by each group.
Such is the scope of the present treatise.
My second, and much more important object, is that of considering the
facts of animal intelligence in their relation to the theory of Descent.
With the exception of Mr. Darwin's admirable chapters on the mental
powers and moral sense, and Mr. Spencer's great work on the Principles
of Psychology, there has hitherto been no earnest attempt at tracing the
principles which have been probably concerned in the genesis of Mind.
Yet there is not a doubt that, for the present generation at all
events, no subject of scientific inquiry can present a higher degree of
interest; and therefore it is mainly with the view of furthering this
inquiry that I have undertaken this work. It will thus be apparent that
the present volume, while complete in itself as a statement of the facts
of Comparative Psychology, has for its more ultimate purpose the laying
of a firm foundation for my future treatise on Mental Evolution. But
although, from what I have just said, it will be apparent that the
present treatise is preliminary to a more important one, I desire to
emphasise this statement, lest the critics, in being now presented only
with a groundwork on which the picture is eventually to be painted,
should deem that the art displayed is of somewhat too commonplace a
kind. If the present work is read without reference to its ultimate
object of supplying facts for the subsequent deduction of principles, it
may well seem but a small improvement upon the works of the
anecdote-mongers. But if it is remembered that my object in these pages
is the mapping out of animal psychology for the purposes of a subsequent
synthesis, I may fairly claim to receive credit for a sound scientific
intention, even where the only methods at my disposal may incidentally
seem to minister to a mere love of anecdote.
It remains to add a few words on the principles which I have laid down
for my own guidance in the selection and arrangement of facts.
Considering it desirable to cast as wide a net as possible, I have
fished the seas of popular literature as well as the rivers of
scientific writing. The endless multitude of alleged facts which I have
thus been obliged to read, I have found, as may well be imagined,
excessively tedious; and as they are for the most part recorded by
wholly unknown observers, the labour of reading them would have been
useless without some trustworthy principles of selection. The first and
most obvious principle that occurred to me was to regard only those
facts which stood upon the authority of observers well known as
competent; but I soon found that this principle constituted much too
close a mesh. Where one of my objects was to determine the upper limit
of intelligence reached by this and that class, order, or species of
animals, I usually found that the most remarkable instances of the
display of intelligence were recorded by persons bearing names more or
less unknown to fame. This, of course, is what we might antecedently
expect, as it is obvious that the chances must always be greatly against
the more intelligent individuals among animals happening to fall under
the observation of the more intelligent individuals among men. Therefore
I soon found that I had to choose between neglecting all the more
important part of the evidence--and consequently in most cases feeling
sure that I had fixed the upper limit of intelligence too low--or
supplementing the principle of looking to authority alone with some
other principles of selection, which, while embracing the enormous class
of alleged facts recorded by unknown observers, might be felt to meet
the requirements of a reasonably critical method. I therefore adopted
the following principles as a filter to this class of facts. First,
never to accept an alleged fact without the authority of some name.
Second, in the case of the name being unknown, and the alleged fact of
sufficient importance to be entertained, carefully to consider whether,
from all the circumstances of the case as recorded, there was any
considerable opportunity for mal-observation; this principle generally
demanded that the alleged fact, or action on the part of the animal,
should be of a particularly marked and unmistakable kind, looking to the
end which the action is said to have accomplished. Third, to tabulate
all important observations recorded by unknown observers, with the view
of ascertaining whether they have ever been corroborated by similar or
analogous observations made by other and independent observers. This
principle I have found to be of great use in guiding my selection of
instances, for where statements of fact which present nothing
intrinsically improbable are found to be unconsciously confirmed by
different observers, they have as good a right to be deemed trustworthy
as statements which stand on the single authority of a known observer,
and I have found the former to be at least as abundant as the latter.
Moreover, by getting into the habit of always seeking for corroborative
cases, I have frequently been able to substantiate the assertions of
known observers by those of other observers as well or better known.
So much, then, for the principles by which I have been guided in the
selection of facts. As to the arrangement of the facts, I have taken the
animal kingdom in ascending order, and endeavoured to give as full a
sketch as the selected evidence at my disposal permitted of the
psychology which is distinctive of each class, or order, and, in some
cases, family, genus, or even species. The reason of my entering into
greater detail with some natural groups than with others scarcely
requires explanation. For it is almost needless to say that if the
animal kingdom were classified with reference to Psychology instead of
with reference to Anatomy, we should have a very different kind of
zoological tree from that which is now given in our diagrams. There is,
indeed, a general and, philosophically considered, most important
parallelism running through the whole animal kingdom between structural
affinity and mental development; but this parallelism is exceedingly
rough, and to be traced only in broad outlines, so that although it is
convenient for the purpose of definite arrangement to take the animal
kingdom in the order presented by zoological classification, it would be
absurd to restrict an inquiry into Animal Psychology by any
considerations of the apparently disproportionate length and minute
subdivision with which it is necessary to treat some of the groups.
Anatomically, an ant or a bee does not require more consideration than a
beetle or a fly; but psychologically there is need for as great a
difference of treatment as there is in the not very dissimilar case of a
monkey and a man.
Throughout the work my aim has been to arrive at definite principles
rather than to chronicle mere incidents--an aim which will become more
apparent when the work as a whole shall have been completed. Therefore
it is that in the present volume I have endeavoured, as far as the
nature and circumstances of the inquiry would permit, to suppress
anecdote. Nevertheless, although I have nowhere introduced anecdotes for
their own sake, I have found it unavoidable not to devote much the
largest part of the present essay to their narration. Hence, with the
double purpose of limiting the introduction of anecdotes as much as
possible, and of not repeating more than I could help anecdotes already
published, I have in all cases, where I could do so without detriment to
my main object, given the preference to facts which have been
communicated to me by friends and correspondents. And here I may fitly
take the opportunity of expressing my thanks and obligations to the
latter, who in astonishing numbers have poured in their communications
during several years from all quarters of the globe. I make this
statement because I desire to explain to all my correspondents who may
read this book, that I am not the less sensible of their kindness
because its bounty has rendered it impossible for me to send
acknowledgments in individual cases. However, I should like to add in
this connection that it does not follow, because I have only quoted a
small percentage of the letters which I have received, that all of the
remainder have been useless. On the contrary, many of these have served
to convey information and suggestions which, even if not reserved for
express quotation in my forthcoming work, have been of use in guiding my
judgment on particular points. Therefore I hope that the publication of
these remarks may serve to swell the stream of communications into a yet
larger flow.[1]
In all cases where I have occasion to quote statements of fact, which in
the present treatise are necessarily numerous, I have made a point of
trying to quote _verbatim_. Only where I have found that the account
given by an author or a correspondent might profitably admit of a
considerable degree of condensation have I presented it in my own words.
And here I have to express my very special obligations to Mr. Darwin,
who not only assisted me in the most generous manner with his immense
stores of information, as well as with his valuable judgment on sundry
points of difficulty, but has also been kind enough to place at my
disposal all the notes and clippings on animal intelligence which he has
been collecting for the last forty years, together with the original MS.
of his wonderful chapter on 'Instinct.' This chapter, on being re-cast
for the 'Origin of Species,' underwent so merciless an amount of
compression that the original draft constitutes a rich store of hitherto
unpublished material. In my second work I shall have occasion to draw
upon this store more largely than in the present one, and it is needless
to add that in all cases where I do draw upon it I shall be careful to
state the source to which I am indebted.
[The above was written when I sent this work to the publishers several
months ago, and I have thought it best to leave the concluding paragraph
as it originally stood. But in making this explanation, I cannot allude
to the calamity which has since occurred without paying my tribute, not
alone to the memory of the greatest genius of our age, but still more,
and much more, to the memory of a friend so inexpressibly noble, kind,
and generous, that even my immense admiration of the naturalist was
surpassed by my loving veneration for the man.]
FOOTNOTES:
[1] Letters may be addressed to me directly at 18 Cornwall Terrace,
Regent's Park, London, N W.
CONTENTS.
PAGE
INTRODUCTION 1
CHAPTER I.
APPLICATION OF THE FOREGOING PRINCIPLES TO THE LOWEST ANIMALS 18
CHAPTER II.
MOLLUSCA 25
CHAPTER III.
ANTS 31
CHAPTER IV.
BEES AND WASPS 143
CHAPTER V.
TERMITES 198
CHAPTER VI.
SPIDERS AND SCORPIONS 204
CHAPTER VII.
REMAINING ARTICULATA 226
CHAPTER VIII.
FISH 241
CHAPTER IX.
BATRACHIANS AND REPTILES 254
CHAPTER X.
BIRDS 266
CHAPTER XI.
MAMMALS 326
CHAPTER XII.
RODENTS 353
CHAPTER XIII.
ELEPHANT 386
CHAPTER XIV.
THE CAT 411
CHAPTER XV.
FOXES, WOLVES, JACKALS, &C. 426
CHAPTER XVI.
THE DOG 437
CHAPTER XVII.
MONKEYS, APES, AND BABOONS 471
INDEX 499
INTRODUCTION.
BEFORE we begin to consider the phenomena of mind throughout the animal
kingdom it is desirable that we should understand, as far as possible,
what it is that we exactly mean by mind. Now, by mind we may mean two
very different things, according as we contemplate it in our own
individual selves, or in other organisms. For if we contemplate our own
mind, we have an immediate cognizance of a certain flow of thoughts or
feelings, which are the most ultimate things, and indeed the only
things, of which we are cognisant. But if we contemplate mind in other
persons or organisms, we have no such immediate cognizance of thoughts
or feelings. In such cases we can only _infer_ the existence and the
nature of thoughts and feelings from the activities of the organisms
which appear to exhibit them. Thus it is that we may have a subjective
analysis of mind and an objective analysis of mind--the difference
between the two consisting in this, that in our subjective analysis we
are restricted to the limits of a single isolated mind which we call our
own, and within the territory of which we have immediate cognizance of
all the processes that are going on, or at any rate of all the processes
that fall within the scope of our introspection. But in our objective
analysis of other or foreign minds we have no such immediate cognizance;
all our knowledge of their operations is derived, as it were, through
the medium of ambassadors--these ambassadors being the activities of the
organism. Hence it is evident that in our study of animal intelligence
we are wholly restricted to the objective method. Starting from what I
know subjectively of the operations of my own individual mind, and the
activities which in my own organism they prompt, I proceed by analogy to
infer from the observable activities of other organisms what are the
mental operations that underlie them.
Now, in this mode of procedure what is the kind of activities which may
be regarded as indicative of mind? I certainly do not so regard the
flowing of a river or the blowing of the wind. Why? First, because the
objects are too remote in kind from my own organism to admit of my
drawing any reasonable analogy between them and it; and, secondly,
because the activities which they present are of invariably the same
kind under the same circumstances; they afford no evidence of feeling or
purpose. In other words, two conditions require to be satisfied before
we even begin to imagine that observable activities are indicative of
mind: first, the activities must be displayed by a living organism; and
secondly, they must be of a kind to suggest the presence of two elements
which we recognise as the distinctive characteristics of mind as
such--consciousness and choice.
So far, then, the case seems simple enough. Wherever we see a living
organism apparently exerting intentional choice, we might infer that it
is conscious choice, and therefore that the organism has a mind. But
further reflection shows us that this is just what we cannot do; for
although it is true that there is no mind without the power of conscious
choice, it is not true that all apparent choice is due to mind. In our
own organisms, for instance, we find a great many adaptive movements
performed without choice or even consciousness coming into play at
all--such, for instance, as in the beating of our hearts. And not only
so, but physiological experiments and pathological lesions prove that in
our own and in other organisms the mechanism of the nervous system is
sufficient, without the intervention of consciousness, to produce
muscular movements of a highly co-ordinate and apparently intentional
character. Thus, for instance, if a man has his back broken in such a
way as to sever the nervous connection between his brain and lower
extremities, on pinching or tickling his feet they are drawn suddenly
away from the irritation, although the man is quite unconscious of the
adaptive movement of his muscles; the lower nerve-centres of the spinal
cord are competent to bring about this movement of adaptive response
without requiring to be directed by the brain. This non-mental operation
of the lower nerve-centres in the production of apparently intentional
movements is called Reflex Action, and the cases of its occurrence, even
within the limits of our own organism, are literally numberless.
Therefore, in view of such non-mental nervous adjustment, leading to
movements which are only in appearance intentional, it clearly becomes a
matter of great difficulty to say in the case of the lower animals
whether any action which appears to indicate intelligent choice is not
really action of the reflex kind.
On this whole subject of mind-like and yet not truly mental action I
shall have much to say in my subsequent treatise, where I shall be
concerned among other things with tracing the probable genesis of mind
from non-mental antecedents. But here it is sufficient merely to make
this general statement of the fact, that even within the experience
supplied by our own organisms adaptive movements of a highly complex and
therefore apparently purposive character may be performed without any
real purpose, or even consciousness of their performance. It thus
becomes evident that before we can predicate the bare existence of mind
in the lower animals, we need some yet more definite criterion of mind
than that which is supplied by the adaptive actions of a living
organism, howsoever apparently intentional such actions may be. Such a
criterion I have now to lay down, and I think it is one that is as
practically adequate as it is theoretically legitimate.
Objectively considered, the only distinction between adaptive movements
due to reflex action and adaptive movements due to mental perception,
consists in the former depending on inherited mechanisms within the
nervous system being so constructed as to effect _particular_ adaptive
movements in response to _particular_ stimulations, while the latter
are independent of any such inherited adjustment of special mechanisms
to the exigencies of special circumstances. Reflex actions under the
influence of their appropriate stimuli may be compared to the actions of
a machine under the manipulations of an operator; when certain springs
of action are touched by certain stimuli, the whole machine is thrown
into appropriate movement; there is no room for choice, there is no room
for uncertainty; but as surely as any of these inherited mechanisms are
affected by the stimulus with reference to which it has been constructed
to act, so surely will it act in precisely the same way as it always has
acted. But the case with conscious mental adjustment is quite different.
For, without at present going into the question concerning the relation
of body and mind, or waiting to ask whether cases of mental adjustment
are not really quite as _mechanical_ in the sense of being the necessary
result or correlative of a chain of physical sequences due to a physical
stimulation, it is enough to point to the variable and incalculable
character of mental adjustments as distinguished from the constant and
foreseeable character of reflex adjustments. All, in fact, that in an
objective sense we can mean by a mental adjustment is an adjustment of a
kind that has not been definitely fixed by heredity as the only
adjustment possible in the given circumstances of stimulation. For were
there no alternative of adjustment, the case, in an animal at least,
would be indistinguishable from one of reflex action.
It is, then, adaptive action by a living organism in cases where the
inherited machinery of the nervous system does not furnish data for our
prevision of what the adaptive action must necessarily be--it is only
here that we recognise the objective evidence of mind. The criterion of
mind, therefore, which I propose, and to which I shall adhere throughout
the present volume, is as follows:--Does the organism learn to make new
adjustments, or to modify old ones, in accordance with the results of
its own individual experience? If it does so, the fact cannot be due
merely to reflex action in the sense above described, for it is
impossible that heredity can have provided in advance for innovations
upon, or alterations of, its machinery during the lifetime of a
particular individual.
In my next work I shall have occasion to consider this criterion of mind
more carefully, and then it will be shown that as here stated the
criterion is not rigidly exclusive, either, on the one hand, of a
possibly mental element in apparently non-mental adjustments, or,
conversely, of a possibly non-mental element in apparently mental
adjustments. But, nevertheless, the criterion is the best that is
available, and, as it will be found sufficient for all the purposes of
the present work, its more minute analysis had better be deferred till I
shall have to treat of the probable evolution of mind from non-mental
antecedents. I may, however, here explain that in my use of this
criterion I shall always regard it as fixing only the upper limit of
non-mental action; I shall never regard it as fixing the lower limit of
mental action. For it is clear that long before mind has advanced
sufficiently far in the scale of development to become amenable to the
test in question, it has probably begun to dawn as nascent subjectivity.
In other words, because a lowly organised animal does _not_ learn by its
own individual experience, we may not therefore conclude that in
performing its natural or ancestral adaptations to appropriate stimuli
consciousness, or the mind-element, is wholly absent; we can only say
that this element, if present, reveals no evidence of the fact. But, on
the other hand, if a lowly organised animal _does_ learn by its own
individual experience, we are in possession of the best available
evidence of conscious memory leading to intentional adaptation.
Therefore our criterion applies to the upper limit of non-mental action,
not to the lower limit of mental.
Of course to the sceptic this criterion may appear unsatisfactory, since
it depends, not on direct knowledge, but on inference. Here, however, it
seems enough to point out, as already observed, that it is the best
criterion available; and further, that scepticism of this kind is
logically bound to deny evidence of mind, not only in the case of the
lower animals, but also in that of the higher, and even in that of men
other than the sceptic himself. For all objections which could apply to
the use of this criterion of mind in the animal kingdom would apply with
equal force to the evidence of any mind other than that of the
individual objector. This is obvious, because, as I have already
observed, the only evidence we can have of objective mind is that which
is furnished by objective activities; and as the subjective mind can
never become assimilated with the objective so as to learn by direct
feeling the mental processes which there accompany the objective
activities, it is clearly impossible to satisfy any one who may choose
to doubt the validity of inference, that in any case other than his own
mental processes ever do accompany objective activities. Thus it is that
philosophy can supply no demonstrative refutation of idealism, even of
the most extravagant form. Common sense, however, universally feels that
analogy is here a safer guide to truth than the sceptical demand for
impossible evidence; so that if the objective existence of other
organisms and their activities is granted--without which postulate
comparative psychology, like all the other sciences, would be an
unsubstantial dream--common sense will always and without question
conclude that the activities of organisms other than our own, when
analogous to those activities of our own which we know to be accompanied
by certain mental states, are in them accompanied by analogous mental
states.
The theory of animal automatism, therefore, which is usually attributed
to Descartes (although it is not quite clear how far this great
philosopher really entertained the theory), can never be accepted by
common sense; and even as a philosophical speculation it will be seen,
from what has just been said, that by no feat of logic is it possible to
make the theory apply to animals to the exclusion of man. The expression
of fear or affection by a dog involves quite as distinctive and complex
a series of neuro-muscular actions as does the expression of similar
emotions by a human being; and therefore, if the evidence of
corresponding mental states is held to be inadequate in the one case, it
must in consistency be held similarly inadequate in the other. And
likewise, of course, with all other exhibitions of mental life.
It is quite true, however, that since the days of Descartes--or rather,
we might say, since the days of Joule--the question of animal automatism
has assumed a new or more defined aspect, seeing that it now runs
straight into the most profound and insoluble problem that has ever been
presented to human thought--viz. the relation of body to mind in view of
the doctrine of the conservation of energy. I shall subsequently have
occasion to consider this problem with the close attention that it
demands; but in the present volume, which has to deal only with the
phenomena of mind as such, I expressly pass the problem aside as one
reserved for separate treatment. Here I desire only to make it plain
that the mind of animals must be placed in the same category, with
reference to this problem, as the mind of man; and that we cannot
without gross inconsistency ignore or question the evidence of mind in
the former, while we accept precisely the same kind of evidence as
sufficient proof of mind in the latter.
And this proof, as I have endeavoured to show, is in all cases and in
its last analysis the fact of a living organism showing itself able to
learn by its own individual experience. Wherever we find an animal able
to do this, we have the same right to predicate mind as existing in such
an animal that we have to predicate it as existing in any human being
other than ourselves. For instance, a dog has always been accustomed to
eat a piece of meat when his organism requires nourishment, and when his
olfactory nerves respond to the particular stimulus occasioned by the
proximity of the food. So far, it may be said, there is no evidence of
mind; the whole series of events comprised in the stimulations and
muscular movements may be due to reflex action alone. But now suppose
that by a number of lessons the dog has been taught not to eat the meat
when he is hungry until he receives a certain verbal signal: then we
have exactly the same kind of evidence that the dog's actions are
prompted by mind as we have that the actions of a man are so
prompted.[2] Now we find that the lower down we go in the animal
kingdom, the more we observe reflex action, or non-mental adjustment, to
predominate over volitional action, or mental adjustment. That is to
say, the lower down we go in the animal kingdom, the less capacity do we
find for changing adjustive movements in correspondence with changed
conditions; it becomes more and more hopeless to _teach_ animals--that
is, to establish associations of ideas; and the reason of this, of
course, is that ideas or mental units become fewer and less definite the
lower we descend through the structure of mind.
* * * * *
It is not my object in the present work to enter upon any analysis of
the operations of mind, as this will require to be done as fully as
possible in my next work. Nevertheless, a few words must here be said
with regard to the main divisions of mental operation, in order to
define closely the meanings which I shall attach to certain terms
relating to these divisions, and the use of which I cannot avoid.
The terms sensation, perception, emotion, and volition need not here be
considered. I shall use them in their ordinary psychological
significations; and although I shall subsequently have to analyse each
of the organic or mental states which they respectively denote, there
will be no occasion in the present volume to enter upon this subject. I
may, however, point out one general consideration to which I shall
throughout adhere. Taking it for granted that the external indications
of mental processes which we observe in animals are trustworthy, so that
we are justified in inferring particular mental states from particular
bodily actions, it follows that in consistency we must everywhere apply
the same criteria.
For instance, if we find a dog or a monkey exhibiting marked expressions
of affection, sympathy, jealousy, rage, &c., few persons are sceptical
enough to doubt that the complete analogy which these expressions afford
with those which are manifested by man, sufficiently prove the
existence of mental states analogous to those in man of which these
expressions are the outward and visible signs. But when we find an ant
or a bee apparently exhibiting by its actions these same emotions, few
persons are sufficiently non-sceptical not to doubt whether the outward
and visible signs are here trustworthy as evidence of analogous or
corresponding inward and mental states. The whole organisation of such a
creature is so different from that of a man that it becomes questionable
how far analogy drawn from the activities of the insect is a safe guide
to the inferring of mental states--particularly in view of the fact that
in many respects, such as in the great preponderance of 'instinct' over
'reason,' the psychology of an insect is demonstrably a widely different
thing from that of a man. Now it is, of course, perfectly true that the
less the resemblance the less is the value of any analogy built upon the
resemblance, and therefore that the inference of an ant or a bee feeling
sympathy or rage is not so valid as is the similar inference in the case
of a dog or a monkey. Still it _is_ an inference, and, so far as it
goes, a valid one--being, in fact, the only inference available. That is
to say, if we observe an ant or a bee apparently exhibiting sympathy or
rage, we must either conclude that some psychological state resembling
that of sympathy or rage is present, or else refuse to think about the
subject at all; from the observable facts there is no other inference
open. Therefore, having full regard to the progressive weakening of the
analogy from human to brute psychology as we recede through the animal
kingdom downwards from man, still, as it is the only analogy available,
I shall follow it throughout the animal series.
It may not, however, be superfluous to point out that if we have full
regard to this progressive weakening of the analogy, we must feel less
and less certain of the real similarity of the mental states compared;
so that when we get down as low as the insects, I think the most we can
confidently assert is that the known facts of human psychology furnish
the best available pattern of the probable facts of insect psychology.
Just as the theologians tell us--and logically enough--that if there is
a Divine Mind, the best, and indeed only, conception we can form of it
is that which is formed on the analogy, however imperfect, supplied by
the human mind; so with 'inverted anthropomorphism' we must apply a
similar consideration with a similar conclusion to the animal mind. The
mental states of an insect may be widely different from those of a man,
and yet most probably the nearest conception that we can form of their
true nature is that which we form by assimilating them to the pattern of
the only mental states with which we are actually acquainted. And this
consideration, it is needless to point out, has a special validity to
the evolutionist, inasmuch as upon his theory there must be a
psychological, no less than a physiological, continuity extending
throughout the length and breadth of the animal kingdom.
* * * * *
In these preliminary remarks only one other point requires brief
consideration, and this has reference to the distinction between what in
popular phraseology is called 'Instinct' and 'Reason.' I shall not here
enter upon any elaborate analysis of a distinction which is undoubtedly
valid, but shall confine my remarks to explaining the sense in which I
shall everywhere use these terms.
Few words in our language have been subject to a greater variety of
meanings than the word instinct. In popular phraseology, descended from
the Middle Ages, all the mental faculties of the animal are termed
instinctive, in contradistinction to those of man, which are termed
rational. But unless we commit ourselves to an obvious reasoning in a
circle, we must avoid assuming that all actions of animals are
instinctive, and then arguing that because they are instinctive,
therefore they differ from the rational actions of man. The question
really lies in what is here assumed, and we can only answer it by
examining in what essential respect instinct differs from reason.
Again, Addison says:--
I look upon instinct as upon the principle of
gravitation in bodies, which is not to be explained by
any known qualities inherent in the bodies themselves,
nor from any laws of mechanism, but as an immediate
impression from the first Mover, and the Divine energy
acting in the creatures.
This mode of 'looking upon instinct' is merely to exclude the subject
from the sphere of inquiry, and so to abstain from any attempt at
definition.
Innumerable other opinions might be quoted from well-known writers,
'looking upon instinct' in widely different ways; but as this is not an
historical work, I shall pass on at once to the manner in which science
looks upon it, or, at least, the manner in which it will always be
looked upon throughout the present work.
Without concerning ourselves with the origin of instincts, and so
without reference to the theory of evolution, we have to consider the
most conspicuous and distinctive features of instinct as it now exists.
The most important point to observe in the first instance is that
instinct involves _mental_ operations; for this is the only point that
serves to distinguish instinctive action from reflex. Reflex action, as
already explained, is non-mental neuro-muscular adaptation to
appropriate stimuli; but instinctive action is this and something more;
there is in it the element of mind. Such, at least, is instinctive
action in the sense that I shall always allude to it. I am, of course,
aware that the limitation which I thus impose is one which is ignored,
or not recognised, by many writers even among psychologists; but I am
persuaded that if we are to have any approach to definiteness in the
terms which we employ--not to say of clearness in our ideas concerning
the things of which we speak--it is most desirable to restrict the word
instinct to mental as distinguished from non-mental activity. No doubt
it is often difficult, or even impossible, to decide whether or not a
given action implies the presence of the mind-element--_i.e._, conscious
as distinguished from unconscious adaptation; but this is altogether a
separate matter, and has nothing to do with the question of defining
instinct in a manner which shall be formally exclusive, on the one hand
of reflex action, and on the other of reason. As Virchow truly observes,
'it is difficult or impossible to draw the line between instinctive and
reflex action;' but at least the difficulty may be narrowed down to
deciding in particular cases whether or not an action falls into this or
that category of definition; there is no reason why the difficulty
should arise on account of any ambiguity of the definitions themselves.
Therefore I endeavour to draw as sharply as possible the line which _in
theory_ should be taken to separate instinctive from reflex action; and
this line, as I have already said, is constituted by the boundary of
non-mental or unconscious adjustment, with adjustment in which there is
concerned consciousness or mind.
Having thus, I hope, made it clear that the difficulty of drawing a
distinction between reflex and instinctive actions as a class is one
thing, and that the difficulty of assigning particular actions to one or
the other of our categories is another thing, we may next perceive that
the former difficulty is obviated by the distinction which I have
imposed, and that the latter only arises from the fact that on the
objective side there is no distinction imposable. The former difficulty
is obviated by the distinction which I have drawn, simply because the
distinction is itself a definite one. In particular cases of adjustive
action we may not always be able to affirm whether consciousness of
their performance is present or absent; but, as I have already said,
this does not affect the validity of our definition; all we can say of
such cases is that if the performance in question is attended with
consciousness it is instinctive, and if not it is reflex.
And the difficulty of assigning particular actions to one or other of
these two categories arises, as I have said, merely because on the
objective side, or the side of the nervous system, there is no
distinction to be drawn. Whether or not a neural process is accompanied
by a mental process, it is in itself the same. The advent and
development of consciousness, although progressively converting reflex
action into instinctive, and instinctive into rational, does this
exclusively in the sphere of subjectivity; the nervous processes engaged
are throughout the same in kind, and differ only in the relative degrees
of their complexity. Therefore, as the dawn of consciousness or the rise
of the mind-element is gradual and undefined, both in the animal kingdom
and in the growing child, it is but necessary that in the early morning,
as it were, of consciousness any distinction between the mental and the
non-mental should be obscure, and generally impossible to determine.
Thus, for instance, a child at birth does not close its eyes upon the
near approach of a threatening body, and it only learns to do so by
degrees as the result of experience; at first, therefore, the action of
closing the eyelids in order to protect the eyes may be said to be
instinctive, in that it involves the mind-element:[3] yet it afterwards
becomes a reflex which asserts itself even in opposition to the will.
And, conversely, sucking in a new-born child, or a child _in utero_, is,
in accordance with my definition, a reflex action; yet in later life,
when consciousness becomes more developed and the child _seeks_ the
breast, sucking may properly be called an instinctive action. Therefore
it is that, as in the ascending scale of objective complexity the
mind-element arises and advances gradually, many particular cases which
occupy the undefined boundary between reflex action and instinct cannot
be assigned with confidence either to the one region or to the other.
We see then the point, and the only point, wherein instinct can be
consistently separated from reflex action; viz., in presenting a mental
constituent. Next we must consider wherein instinct may be separated
from reason. And for this purpose we may best begin by considering what
we mean by reason.
The term 'reason' is used in significations almost as various as those
which are applied to 'instinct.' Sometimes it stands for all the
distinctively human faculties taken collectively, and in antithesis to
the mental faculties of the brute; while at other times it is taken to
mean the distinctively human faculties of intellect.
Dr. Johnson defines it as 'the power by which man deduces one
proposition from another, and proceeds from premises to consequences.'
This definition presupposes language, and therefore ignores all cases of
inference not thrown into the formal shape of predication. Yet even in
man the majority of inferences drawn by the mind never emerge as
articulate propositions; so that although, as we shall have occasion
fully to observe in my subsequent work, there is much profound
philosophy in identifying reason with speech as they were identified in
the term Logos, yet for purposes of careful definition so to identify
intellect with language is clearly a mistake.
More correctly, the word reason is used to signify the power of
perceiving analogies or ratios, and is in this sense equivalent to the
term 'ratiocination,' or the faculty of deducing inferences from a
perceived equivalency of relations. Such is the only use of the word
that is strictly legitimate, and it is thus that I shall use it
throughout the present treatise. This faculty, however, of balancing
relations, drawing inferences, and so of forecasting probabilities,
admits of numberless degrees; and as in the designation of its lower
manifestations it sounds somewhat unusual to employ the word reason, I
shall in these cases frequently substitute the word intelligence. Where
we find, for instance, that an oyster profits by individual experience,
or is able to perceive new relations and suitably to act upon the result
of its perceptions, I think it sounds less unusual to speak of the
oyster as displaying intelligence than as displaying reason. On this
account I shall use the former term to signify the lower degrees of the
ratiocinative faculty; and thus in my usage it will be opposed to such
terms as instinct, reflex action, &c., in the same manner as the term
reason is so opposed. This is a point which, for the sake of clearness,
I desire the reader to retain in his memory. I shall always speak of
intelligence and intellect in antithesis to instinct, emotion, and the
rest, as implying mental faculties the same in kind as those which in
ourselves we call rational.
Now it is notorious that no distinct line can be drawn between instinct
and reason. Whether we look to the growing child or to the ascending
scale of animal life, we find that instinct shades into reason by
imperceptible degrees, or, as Pope expresses it, that these principles
are 'for ever separate, yet for ever near.' Nor is this other than the
principles of evolution would lead us to expect, as I shall afterwards
have abundant occasion to show. Here, however, we are only concerned
with drawing what distinction we can between instinct and reason as
these faculties are actually presented to our observation. And this in a
general way it is not difficult to do.
We have seen that instinct involves 'mental operations,' and that by
this feature it is distinguished from reflex action; we have now to
consider the features by which it is distinguished from reason. These
are accurately, though not completely, conveyed by Sir Benjamin Brodie,
who defines instinct as 'a principle by which animals are induced,
independently of experience and reasoning, to the performances of
certain voluntary acts, which are necessary to their preservation as
individuals, or to the continuance of the species, or in some other way
convenient to them.'[4] This definition, as I have said, is accurate as
far as it goes, but it does not state with sufficient generality and
terseness that all instinctive action is adaptive; nor does it clearly
bring out the distinction between instinct and reason which is thus well
conveyed by the definition of Hartmann, who says in his 'Philosophy of
the Unconscious,' that 'instinct is action taken in pursuance of an end,
but without conscious perception of what the end is.' This definition,
however, is likewise defective in that it omits another of the important
differentiæ of instinct--namely, the uniformity of instinctive action as
performed by different individuals of the same species. Including this
feature, therefore, we may more accurately and completely define
instinct as mental action (whether in animals or human beings),
directed towards the accomplishing of adaptive movement, antecedent to
individual experience, without necessary knowledge of the relation
between the means employed and the ends attained, but similarly
performed under the same appropriate circumstances by all the
individuals of the same species. Now in every one of these respects,
with the exception of containing a mental constituent and in being
concerned in adaptive action, instinct differs from reason. For reason,
besides involving a mental constituent, and besides being concerned in
adaptive action, is always subsequent to individual experience, never
acts but upon a definite and often laboriously acquired knowledge of the
relation between means and ends, and is very far from being always
similarly performed under the same appropriate circumstances by all the
individuals of the same species.
Thus the distinction between instinct and reason is both more definite
and more manifold than is that between instinct and reflex action.
Nevertheless, in particular cases there is as much difficulty in
classifying certain actions as instinctive or rational, as there is in
cases where the question lies between instinct and reflex action. And
the explanation of this is, as already observed, that instinct passes
into reason by imperceptible degrees; so that actions in the main
instinctive are very commonly tempered with what Pierre Huber calls 'a
little dose of judgment or reason,' and _vice versâ_. But here, again,
the difficulty which attaches to the classification of particular
actions has no reference to the validity of the distinctions between the
two classes of actions; these are definite and precise, whatever
difficulty there may be in applying them to particular cases.
Another point of difference between instinct and reason may be noticed
which, although not of invariable, is of very general applicability. It
will have been observed, from what has already been said, that the
essential respect in which instinct differs from reason consists in the
amount of conscious deliberation which the two processes respectively
involve. Instinctive actions are actions which, owing to their frequent
repetition, become so habitual in the course of generations that all
the individuals of the same species automatically perform the same
actions under the stimulus supplied by the same appropriate
circumstances. Rational actions, on the other hand, are actions which
are required to meet circumstances of comparatively rare occurrence in
the life-history of the species, and which therefore can only be
performed by an intentional effort of adaptation. Consequently there
arises the subordinate distinction to which I allude, viz., that
instinctive actions are only performed under particular circumstances
which have been frequently experienced during the life-history of the
species; whereas rational actions are performed under varied
circumstances, and serve to meet novel exigencies which may never before
have occurred even in the life-history of the individual.
Thus, then, upon the whole, we may lay down our several definitions in
their most complete form.
Reflex action is non-mental neuro-muscular adjustment, due to the
inherited mechanism of the nervous system, which is formed to respond to
particular and often recurring stimuli, by giving rise to particular
movements of an adaptive though not of an intentional kind.
Instinct is reflex action into which there is imported the element of
consciousness. The term is therefore a generic one, comprising all those
faculties of mind which are concerned in conscious and adaptive action,
antecedent to individual experience, without necessary knowledge of the
relation between means employed and ends attained, but similarly
performed under similar and frequently recurring circumstances by all
the individuals of the same species.
Reason or intelligence is the faculty which is concerned in the
intentional adaptation of means to ends. It therefore implies the
conscious knowledge of the relation between means employed and ends
attained, and may be exercised in adaptation to circumstances novel
alike to the experience of the individual and to that of the species.
FOOTNOTES:
[2] Of course it may be said that we have no evidence of _prompting_ in
either case; but this is the side issue which concerns the general
relation of body and mind, and has nothing to do with the guarantee of
inferring the presence of mind in particular cases.
[3] _I.e._, ancestral as well as individual. If the race had not always
had occasion to close the eyelids to protect the eyes, it is certain
that the young child would not so quickly learn to do so in virtue of
its own individual experience alone; and as the action cannot be
attributed to any process of conscious inference, it is not rational;
but we have seen that it is not originally reflex; therefore it is
instinctive.
[4] _Psychological Researches_, p. 187.
CHAPTER I.
APPLICATION OF THE FOREGOING PRINCIPLES TO THE LOWEST ANIMALS.
_Protozoa._
NO one can have watched the movements of certain Infusoria without
feeling it difficult to believe that these little animals are not
actuated by some amount of intelligence. Even if the manner in which
they avoid collisions be attributed entirely to repulsions set up in the
currents which by their movements they create, any such mechanical
explanation certainly cannot apply to the small creatures seeking one
another for the purposes of prey, reproduction, or, as it sometimes
seems, of mere sport. There is a common and well-known rotifer whose
body is of a cup shape, provided with a very active tail, which is armed
at its extremity with strong forceps. I have seen a small specimen of
this rotifer seize a much larger one with its forceps, and attach itself
by this means to the side of the cup. The large rotifer at once became
very active, and swinging about with its burden until it came to a piece
of weed, it took firm hold of the weed with its own forceps, and began
the most extraordinary series of movements, which were obviously
directed towards ridding itself of the encumbrance. It dashed from side
to side in all directions with a vigour and suddenness which were highly
astonishing, so that it seemed as if the animalcule would either break
its forceps or wrench its tail from its body. No movements could
possibly be better suited to jerk off the offending object, for the
energy with which the jerks were given, now in one direction and now in
another, were, as I have said, most surprising. But not less surprising
was the tenacity with which the smaller rotifer retained its hold; for
although one might think that it was being almost jerked to pieces,
after each bout of jerking it was seen to be still attached. This trial
of strength, which must have involved an immense expenditure of energy
in proportion to the size of the animals, lasted for several minutes,
till eventually the small rotifer was thrown violently away. It then
returned to the conflict, but did not succeed a second time in
establishing its hold. The entire scene was as like intelligent action
on the part of both animals as could well be imagined, so that if we
were to depend upon appearances alone, this one observation would be
sufficient to induce me to attribute conscious determination to these
microscopical organisms.
But, without denying that conscious determination may here be present,
or involving ourselves in the impossible task of proving such a
negative, we may properly affirm that until an animalcule shows itself
to be teachable by individual experience, we have no sufficient evidence
derived or derivable from any number of such apparently intelligent
movements, that conscious determination is present. Therefore, I need
not wait to quote the observations of the sundry microscopists who
detail facts more or less similar to the above, with expressions of
their belief that microscopical organisms display a certain degree of
instinct or intelligence as distinguished from mechanical, or wholly
non-mental adjustment. But there are some observations relating to the
lowest of all animals, and made by a competent person, which are so
remarkable that I shall have to quote them in full. These observations
are recorded by Mr. H. J. Carter, F.R.S., in the 'Annals of Natural
History,' and in his opinion prove that the beginnings of instinct are
to be found so low down in the scale as the Rhizopoda. He says:--'Even
_Athealium_ will confine itself to the water of the watch-glass in which
it may be placed when away from sawdust and chips of wood among which it
has been living; but if the watch-glass be placed upon the sawdust, it
will very soon make its way over the side of the watch-glass and get to
it.'
This is certainly a remarkable observation: for it seems to show that
the rhizopod distinguishes the presence of the sawdust outside the
watch-glass, and crawls over the brim of the latter in order to get into
more congenial quarters, while it is contented with the water in the
watch-glass so long as there is no sawdust outside. But to proceed:
On one occasion, while investigating the nature of
some large, transparent, spore-like elliptical cells
(fungal?) whose protoplasm was rotating, while it was
at the same time charged with triangular grains of
starch, I observed some actinophorous rhizopods
creeping about them, which had similarly shaped grains
of starch in their interior; and having determined the
nature of these grains in both by the addition of
iodine, I cleansed the glasses, and placed under the
microscope a new portion of the sediment from the
basin containing these cells and actinophryans for
further examination, when I observed one of the
spore-like cells had become ruptured, and that a
portion of its protoplasm, charged with the triangular
starch-grains, was slightly protruding through the
crevice. It then struck me that the actinophryans had
obtained their starch-grains from this source; and
while looking at the ruptured cell, an _actinophrys_
made its appearance, and creeping round the cell, at
last arrived at the crevice, from which it extricated
one of the grains of starch mentioned, and then crept
off to a good distance. Presently, however, it
returned to the same cell; and although there were now
no more starch-grains protruding, the _actinophrys_
managed again to extract one from the interior through
the crevice. All this was repeated several times,
showing that the _actinophrys_ instinctively knew that
those were nutritious grains, that they were contained
in this cell, and that, although each time after
incepting a grain it went away to some distance, it
knew how to find its way back to the cell again which
furnished this nutriment.
On another occasion I saw an _actinophrys_ station
itself close to a ripe spore-cell of _pythium_, which
was situated upon a filament of _Spirogyra crassa_;
and as the young ciliated monadic germs issued forth,
one after another, from the dehiscent spore-cell, the
_actinophrys_ remained by it and caught every one of
them, even to the last, when it retired to another
part of the field, as if instinctively conscious that
there was nothing more to be got at the old place.
But by far the greatest feat of this kind that ever
presented itself to me was the catching of a young
_acineta_ by an old sluggish _amoeba_, as the
former left its parent; and this took place as
follows:--
In the evening of the 2nd of June, 1858, in Bombay,
while looking through a microscope at some _Euglenæ_,
&c., which had been placed aside for examination in a
watch-glass, my eye fell upon a stalked and triangular
_acineta_ (_A. mystacina_?), around which an
_amoeba_ was creeping and lingering, as they do when
they are in quest of food. But knowing the antipathy
that the _amoeba_, like almost every other
infusorian, has to the tentacles of the _acineta_, I
concluded that the _amoeba_ was not encouraging an
appetite for its whiskered companion, when I was
surprised to find that it crept up the stem of the
_acineta_, and wound itself round its body. This mark
of affection, too much like that frequently evinced at
the other end of the scale, even where there is a mind
for its control, did not long remain without
interpretation. There was a young _acineta_, tender,
and without poisonous tentacles (for they are not
developed at birth), just ready to make its exit from
the parent, an exit which takes place so quickly, and
is followed by such rapid bounding movements of the
non-ciliated _acineta_, that who would venture to say,
_à priori_, that a dull, heavy, sluggish _amoeba_
could catch such an agile little thing? But the
_amoeba_ are as unerring and unrelaxing in their
grasp as they are unrelenting in their cruel
inceptions of the living and the dead, when they serve
them for nutrition; and thus the _amoeba_, placing
itself round the ovarian aperture of the _acineta_,
received the young one, nurse-like, in its fatal lap,
incepted it, descended from the parent, and crept off.
Being unable to conceive at the time that this was
such an act of atrocity on the part of the _amoeba_
as the sequel disclosed, and thinking that the young
_acineta_ might yet escape, or pass into some other
form in the body of its host, I watched the _amoeba_
for some time afterwards, until the tale ended by the
young _acineta_ becoming divided into two parts, and
thus in their respective digestive spaces ultimately
becoming broken down and digested.[5]
With regard to these remarkable observations it can only, I think, be
said that although certainly very suggestive of something more than
mechanical response to stimulation, they are not sufficiently so to
justify us in ascribing to these lowest members of the zoological scale
any rudiment of truly mental action. The subject, however, is here full
of difficulty, and not the least so on account of the _amoeba_ not
only having no nervous system, but no observable organs of any kind; so
that, although we may suppose that the adaptive movements described by
Mr. Carter were non-mental, it still remains wonderful that these
movements should be exhibited by such apparently unorganised creatures,
seeing that as to the remoteness of the end attained, no less than the
complex refinement of the stimulus to which their adaptive response was
due, the movements in question rival the most elaborate of non-mental
adjustments elsewhere performed by the most highly organised of nervous
systems.
_Coelenterata._
Dr. Eimer attributes 'voluntary action' to the Medusæ, and indeed draws
a sharp distinction between what he considers their 'involuntary' and
'voluntary' movements. In this distinction, however, I do not at all
concur; for although I am well acquainted with the difference between
the active and slow rhythm upon which the distinction is founded, I see
no evidence whatever for supposing that the difference involves any
psychological element. The active swimming is produced by stimulation,
and is no doubt calculated to lead to the escape of the organism; but
this fact certainly does not carry us beyond the ordinary possibilities
of reflex action. And even when, as in some species is constantly the
case, bouts of active swimming appear to arise spontaneously or without
observable stimulation, the fact is to be attributed to a liberation of
overplus ganglionic energy, or to some unobservable stimulation; it does
not justify the supposition of any psychical element being concerned.[6]
M'Crady gives an interesting account of a medusa which carries its larvæ
on the inner sides of its bell-shaped body. The manubrium, or mobile
digestive cavity of the animal, depends, as in the other Medusæ, from
the summit of the concave surface of the bell, like a clapper or tongue.
Now M'Crady observed this depending organ to be moved first to one side
and then to the other side of the bell, in order to give suck to the
larvæ on the sides of the bell--the larvæ dipping their long noses into
the nutrient fluids which that organ of the parent's body contained. I
cite this case, because if it occurred in one of the higher animals it
would probably be called a case of instinct; but as it occurs in so low
an animal as a jelly-fish, it is unreasonable to suppose that
intelligence can ever have played any part in originating the action.
Therefore we may set it down as the uncompounded result of natural
selection.
Some species of medusæ--notably _Sarsia_--seek the light, crowding into
the path of a beam, and following it actively if moved. They derive
advantage from so doing, because certain small crustacea on which they
feed likewise crowd into the light. The seeking of light by these medusæ
is therefore doubtless of the nature of a reflex action which has been
developed by natural selection in order to bring the animals into
contact with their prey. Paul Bert has found that _Daphnia pulex_ seeks
the light (especially the yellow ray), and Engelmann has observed the
same fact with regard to certain protoplasmic organisms. But in none of
these or other such cases is there any evidence of a psychical element
being concerned in the process.
_Echinodermata._
Some of the natural movements of these animals, as also some of their
movements under stimulation, are very suggestive of purpose; but I have
satisfied myself that there is no adequate evidence of the animals being
able to profit by individual experience, and therefore, in accordance
with our canon, that there is no adequate evidence of their exhibiting
truly mental phenomena. On the other hand, the study of reflex action in
these organisms is full of interest--so much so that in my next work I
shall take them as typical organisms in this connection.[7]
_Annelida._
Mr. Darwin has now in the press a highly interesting work on the habits
of earth-worms. It appears from his observations that the manner in
which these animals draw down leaves, &c., into their burrows is
strongly indicative of instinctive action, if not of intelligent
purpose--seeing that they always lay hold of the part of the leaf (even
though an exotic one) by the traction of which the leaf will offer least
resistance to being drawn down. But as this work will so shortly be
published, I shall not forestall any of the facts which it has to state,
nor should I yet like to venture an opinion as to how far these facts,
when considered altogether, would justify any inference to a truly
mental element as existing in these animals.
Of the land leeches in Ceylon, Sir E. Tennent gives an account which
likewise seems to bespeak intelligence as occurring in annelids. He
says:--
In moving, the land leeches have the power of planting
one extremity on the earth and raising the other
perpendicularly to watch for their victim. Such is
their vigilance and instinct, that on the approach of
a passer-by to a spot which they infest, they may be
seen amongst the grass and fallen leaves on the edge
of a native path, poised erect, and preparing for
their attack on man and horse. On descrying their prey
they advance rapidly by semicircular strides, fixing
one end firmly and arching the other forwards, till by
successive advances they can lay hold of the
traveller's foot, when they disengage themselves from
the ground and ascend his dress in search of an
aperture to enter. In these encounters the individuals
in the rear of a party of travellers in the jungle
invariably fare worst, as the leeches, once warned of
their approach, congregate with singular celerity.[8]
FOOTNOTES:
[5] H. J. Carter, F.R.S., _Annals of Natural History_, 3rd Series, 1863,
pp. 45-6.
[6] For an account of the natural movements of the Medusæ and the
effects of stimulation upon them, see Croonian Lecture in _Phil. Trans._
1875, and also _Phil. Trans._ 1877 and 1879.
[7] See Croonian Lecture, 1881, in forthcoming issue of _Phil. Trans._
[8] _Natural History of Ceylon_, p. 481.
CHAPTER II.
MOLLUSCA.
I SHALL treat of the Mollusca before the Articulata, because as a group
their intelligence is not so high. Indeed, it is not to be expected that
the class of animals wherein the 'vegetative' functions of nutrition and
reproduction predominate so largely over the animal functions of
sensation, locomotion, &c., should present any considerable degree of
intelligence. Nevertheless, in the only division of the group which has
sense organs and powers of locomotion highly developed--viz., the
Cephalopoda--we meet with large cephalic ganglia, and, it would appear,
with no small development of intelligence. Taking, however, the
sub-kingdom in ascending order, I shall first present all the
trustworthy evidence that I have been able to collect, pointing to the
highest level of intelligence that is attained by the lower members.
The following is quoted from Mr. Darwin's MS.:--
Even the headless oyster seems to profit from
experience, for Dicquemase ('Journal de Physique,'
vol. xxviii. p. 244) asserts that oysters taken from a
depth never uncovered by the sea, open their shells,
lose the water within, and perish; but oysters taken
from the same place and depth, if kept in reservoirs,
where they are occasionally left uncovered for a short
time, and are otherwise incommoded, learn to keep
their shells shut, and then live for a much longer
time when taken out of the water.[9]
Some evidence of intelligence seems to be displayed by the razor-fish.
For the animals dislike salt, so that when this is sprinkled above their
burrows in the sand, they come to the surface and quit their
habitations. But if the animal is once seized when it comes to the
surface and afterwards allowed to retire into its burrow, no amount of
salt will force it again to come to the surface.[10]
With regard to snails, L. Agassiz writes: 'Quiconque a eu l'occasion
d'observer les amours des limaçons, ne saurait mettre en doute la
séduction déployée dans les mouvements et les allures qui préparent et
accomplissent le double embrassement de ces hermaphrodites.'[11]
Again, Mr. Darwin's MS. quotes from Mr. W. White[12] a curious exhibition
of intelligence in a snail, which does not seem to have admitted of
mal-observation. This gentleman 'fixed a land-shell mouth uppermost in a
chink of rock; in a short time the snail protruded itself to its utmost
length, and, attaching its foot vertically above, tried to pull the
shell out in a straight line. Not succeeding, it rested for a few
minutes and then stretched out its body on the right side and pulled its
utmost, but failed. Resting again, it protruded its foot on the left
side, pulled with its full force, and freed the shell. This exertion of
force in three directions, which seems so geometrically suitable, must
have been intentional.'
If it is objected that snail shells must frequently be liable to be
impeded by obstacles, and therefore that this display of manoeuvring
on the part of their occupants is to be regarded as a reflex, I may
remark that here again we have one of those incessantly recurring cases
where it is difficult to draw the line between intelligence and
non-intelligence. For, granting that the action is to a certain extent
mechanical, we must still recognise that the animal while executing it
must have remembered each of the two directions in which it had pulled
ineffectually before it began to pull in the third direction; and it is
improbable that snail shells are so frequently caught in positions from
which a pull in only one direction will release them, that natural
selection would have developed a special instinct to try pulling
successively in three directions at right angles to one another.
The only other instance that I have met with of the apparent display of
intelligence in snails is the remarkable one which Mr. Darwin gives in
his 'Descent of Man,' on the authority of Mr. Lonsdale. Although the
interpretation which is assigned to the fact seems to me to go beyond
anything that we should have reason to expect of snail intelligence, I
cannot ignore a fact which stands upon the observation of so good an
authority, and shall therefore quote it in Mr. Darwin's words:--
These animals appear also susceptible of some degree
of permanent attachment: an accurate observer, Mr.
Lonsdale, informs me that he placed a pair of
land-snails (_Helix pomatia_), one of which was
weakly, into a small and ill-provided garden. After a
short time the strong and healthy individual
disappeared, and was traced by its track of slime over
a wall into an adjoining well-stocked garden. Mr.
Lonsdale concluded that it had deserted its sickly
mate; but after an absence of twenty-four hours it
returned, and apparently communicated the result of
its successful exploration, for both then started
along the same track, and disappeared over the
wall.[13]
In this case the fact must be accepted, seeing that it stands on the
authority of an accurate observer, and is of so definite a kind as not
to admit of mistake. Consequently we are shut up to the alternative of
supposing the return of the healthy snail to its mate a mere accident,
and their both going over the wall into the well-stocked garden another
mere accident, or acquiescing in the interpretation which Mr. Darwin
assigns. Now, if we look closely into the matter, the chances against
the double accident in question are certainly so considerable as to
render the former supposition almost impossible. On the other hand,
there is evidence to prove, as I shall immediately show, that a not
distantly allied animal is unquestionably able to remember a particular
locality as its home, and habitually to return to this locality after
feeding. Therefore, in view of this analogous and corroborative case,
the improbability of the snail remembering for twenty-four hours the
position of its mate is very much reduced; while the subsequent
communication, if it took place, would only require to have been of the
nature of 'follow me,' which, as we shall repeatedly find, is a degree
of communicative ability which many invertebrated animals possess.
Therefore, in view of these considerations, I incline to Mr. Darwin's
opinion that the facts can only be explained by supposing them due to
intelligence on the part of the snails. Thus considered, these facts are
no doubt very remarkable; for they would appear to indicate not merely
accurate memory of direction and locality for twenty-four hours, but
also no small degree of something akin to 'permanent attachment,' and
sympathetic desire that another should share in the good things which
one has found.[14]
The case to which I have just alluded as proving beyond all doubt that
some Gasteropoda are able to retain a very precise and accurate memory
of locality, is that of the common limpet.
Mr. J. Clarke Hawkshaw publishes in the Journal of the Linnæan Society
the following account of the habits in question:--
The holes in the chalk in which the limpets are often
to be found are, I believe, excavated in a great
measure by rasping from the lingual teeth, though I
doubt whether the object is to form a cavity to
shelter in, though the cavities, when formed, may be
of use for that purpose. It must be of the greatest
importance to a limpet that, in order that it may
insure a firm adherence to the rock, its shell should
fit the rock accurately; when the shell does fit the
rock accurately, a small amount of muscular
contraction of the animal would cause the shell to
adhere so firmly to a smooth surface as to be
practically immoveable without fracture. As the shells
cannot be adapted daily to different forms of surface,
the limpets generally return to the same place of
attachment. I am sure this is the case with many; for
I found shells perfectly adjusted to the uneven
surfaces of flints, the growth of the shells being in
some parts distorted and indented to suit
inequalities in the surface of the flints. . . .
I noticed signs that limpets prefer a hard, smooth
surface to a pit in the chalk. On one surface of a
large block, over all sides of which limpets were
regularly and plentifully distributed, there were two
flat fragments of a fossil shell about 3 inches by 4
inches, each embedded in the chalk. The chalk all
round these fragments was free from limpets; but on
the smooth surface of the pieces of shell they were
packed as closely as they could be. I noticed another
case, which almost amounts, to my mind, to a proof
that they prefer a smooth surface to a hole. A limpet
had formed a clearing on one of the sea-weed-covered
blocks before referred to. In the midst of this
clearing was a pedestal of flint rather more than one
inch in diameter, standing up above the surface of the
chalk; it projected so much that a tap from my hammer
broke it off. On the top of the smooth fractured
surface of this flint the occupant of the clearing had
taken up its abode. The shell was closely adapted to
the uneven surface, which it would only fit in one
position. The cleared surface was in a hollow with
several small natural cavities, where the limpet could
have found a pit ready made to shelter in; yet it
preferred, after each excursion, to climb up to the
top of the flint, the most exposed point in all its
domain.[15]
It appears certain from these observations, which to some extent were
anticipated by those of Mr. F. C. Lukis,[16] that limpets, after every
browsing excursion, return to one particular spot or home; and the
precise memory of direction and locality implied by this fact seems to
justify us in regarding these actions of the animal as of a nature
unquestionably intelligent.
Coming now to the cephalopoda, there is no doubt that if a larger sphere
of opportunity permitted, adequate observation of these animals would
prove them to be much the most intelligent members of the sub-kingdom.
Unfortunately, however, this sphere of opportunity has hitherto been
very limited. The following meagre account is all that I have been able
to gather concerning the psychology of these interesting animals.
According to Schneider,[17] the Cephalopoda show unmistakable evidence
of consciousness and intelligence. This observer had an opportunity of
watching them for a long time in the zoological station at Naples; and
he says that they appeared to recognise their keeper after they had for
some time received their food from him. Hollmann narrates that an
octopus, which had had a struggle with a lobster, followed the latter
into an adjacent tank, to which it had been removed for safety, and
there destroyed it. In order to do this the octopus had to climb up a
vertical partition above the surface of the water and descend the other
side.[18] According to Schneider, the Cephalopoda have an abstract idea
of water, seeking to return to it when removed, even though they do not
see it. But this probably arises from the sense of discomfort due to
exposure of their skin to the air; and if we can call it an 'idea,' it
is doubtless shared by all other aquatic Mollusca when exposed to air.
FOOTNOTES:
[9] This fact is also stated by Bingley, _Animal Biography_, vol. iii.
p. 454, and is now turned to practical account in the so-called
'Oyster-schools' of France. The distance from the coast to Paris being
too great for the newly dredged oysters to travel without opening their
shells, they are first taught in the schools to bear a longer and longer
exposure to the air without gaping, and when their education in this
respect is completed they are sent on their journey to the metropolis,
where they arrive with closed shells, and in a healthy condition.
[10] Bingley, _loc. cit._, vol. iii. p. 449.
[11] _De l'Espèce et de la Classe_, &c., 1869, p. 106.
[12] _A Londoner's Walk to Edinburgh_, p. 155 (1856).
[13] _Descent of Man_, pp. 262-3.
[14] The facts, however, in order to sustain such conclusions, of course
require corroboration, and it is therefore to be regretted that Mr.
Lonsdale did not experimentally repeat the conditions.
[15] _Journal Linn. Soc._ vol. xiv. p. 406 _et seq._
[16] _Mag. Nat. Hist._ 1831, vol. iv. p. 346.
[17] _Thieresche Wille_, § 78.
[18] _Leben der Cephalopoden_, s. 21.
CHAPTER III.
ANTS.
WITHIN the last ten or twelve years our information on the habits and
intelligence of these insects has been so considerably extended, that in
here rendering a condensed epitome of our knowledge in this most
interesting branch of comparative psychology, it will be found that the
chapter is constituted principally of a statement of observations and
experiments which have been conducted during the short period named. The
observers to whom we are mainly indebted for this large increase of our
knowledge are Messrs. Bates, Belt, Müller, Moggridge, Lincecum, MacCook,
and Sir John Lubbock. From the fact that these naturalists conducted
their observations in different parts of the world and on widely
different species of ants, it is not surprising that their results
should present many points of difference; for this only shows, as we
might have expected, that different species of ants differ considerably
in habits and intelligence. Therefore, in now drawing all these numerous
observations to a focus, I shall endeavour to show clearly their points
of difference as well as their points of agreement; and in order that
the facts to be considered may be arranged in some kind of order, I
shall deal with them under the following heads:--Powers of special
sense; Sense of direction; Powers of memory; Emotions; Powers of
communication; Habits general in sundry species; Habits peculiar to
certain species; General intelligence of various species.
_Powers of Special Sense._
Taking first the sense of sight, Sir John Lubbock made a number of
experiments on the influence of light coloured by passing through
various tints of stained glass, with the following results. The ants
which he observed greatly dislike the presence of light within their
nests, hurrying about in search of the darkest corners when light is
admitted. The experiments showed that the dislike is much greater in the
case of some colours than in that of others. Thus under a slip of red
glass there were congregated on one occasion 890 ants, under green 544,
under yellow 495, and under violet only 5. To our eyes the violet is as
opaque as the red, more so than the green, and much more so than the
yellow. Yet, as the numbers show, the ants had scarcely any tendency to
congregate under it: there were nearly as many under the same area of
the uncovered portion of the nest as under that shaded by the violet
glass. It is curious that the coloured glasses appear to act on the ants
in a graduated series, which corresponds with the order of their
influence on a photographic plate. Experiments were therefore made to
test whether it might not be the actinic rays that were so particularly
distasteful to the ants; but with negative results. Placing violet glass
above red produces the same effect as red glass alone. Obviously,
therefore, the ants avoid the violet glass because they dislike the rays
which it transmits, and do not prefer the other colours because they
like the rays which they transmit. Sodium, barium, strontium, and
lithium flames were also tried, but not with so much effect as the
coloured glass.
It has just been observed that the relative dislike which Sir John
Lubbock's ants showed to lights of different colours seems to be
determined by the position of the colour in the spectrum--there being a
regular gradation of intolerance shown from the red to the violet end.
As these ants dislike light, the question suggests itself that the
reason of their graduated intolerance to light of different colours may
be due to their eyes not being so much affected by the rays of low as by
those of high refrangibility. In this connection it would be interesting
to ascertain whether ants of the genus _Atta_ show a similarly graduated
intolerance to the light in different parts of the spectrum; for both
Moggridge and MacCook record of this genus that it not only does not
shun the light, but seeks it--coming to the glass sides of their
artificial nests to enjoy the light of a lamp. Possibly, therefore, the
scale of preference to lights of different colours would be found in
this genus to be the reverse of that which Sir John Lubbock has found in
the case of the British species.
As regards hearing, Sir John Lubbock found that sounds of various kinds
do not produce any effect upon the insects. Tuning-forks and violin
notes, shouting, whistling, &c., were all equally inefficient in
producing the slightest influence upon the animals; and experiments with
sensitive flames, microphone, telephone, &c., failed to yield any
evidence of ants emitting sounds inaudible to human ears.
Lastly, as regards the sense of smell, Sir John Lubbock found that on
bringing a camel's-hair brush steeped in various strong scents near
where ants were passing, "some went on without taking any notice, but
others stopped, and evidently perceiving the smell, turned back. Soon,
however, they returned, and passed the scented pencil. After doing this
two or three times, they generally took no further notice of the scent.
This experiment left no doubt on my mind." In other cases the ants were
observed to wave about and throw back their antennæ when the scented
pencil was brought near.
That ants track one another by scent was long ago mentioned by Huber,
and also that they depend on this sense for their power of finding
supplies which have been previously found by other ants. Huber proved
their power of tracking a path previously pursued by their friends, by
drawing his finger across the trail, so obliterating the scent at that
point, and observing that when the ants arrived at that point they
became confused and ran about in various directions till they again came
upon the trail on the other side of the interrupted space, when they
proceeded on their way as before. The more numerous and systematic
experiments of Sir John Lubbock have fully corroborated Huber's
observations, so far as these points are concerned. Thus, to give only
one or two of these experiments; in the accompanying woodcut (Fig. 1) A
is the nest, B a board, _n_ _f_ _g_ slips of paper, _h_ and _m_ similar
slides of glass, on one of which, _h_, there was placed pupæ, while the
other, _m_, was left empty. Sir John Lubbock watched two particular
(marked) ants proceeding from A to _h_ and back again, carrying the pupæ
on _h_ to the nest A. Whenever an ant came out of A upon B he transposed
the slips _f_ and _g_. Therefore at the angle below _n_ there was a
choice presented to the ant of taking the unscented pathway leading to
the full glass _h_, or the scented pathway leading to the empty glass
_m_. The two marked ants, knowing their way, always took the right turn
at the angle; but the stranger ants, being guided only by scent, for the
most part took the wrong turn at the angle, so going to the empty glass
_m_. For out of 150 stranger ants only 21 went to _h_, while the
remaining 129 went to _m_. Still the fact that all the stranger ants did
not follow the erroneous scent-trail to _m_, may be taken to indicate
that they are also assisted in finding treasure by the sense of sight,
though in a lesser degree. Therefore Sir John Lubbock concludes that in
finding treasure 'they are guided in some cases by sight, while in
others they track one another by scent.'
[Illustration: Fig. 1.]
As further evidence showing how much more ants depend upon scent than
upon sight in finding their way, the following experiment may be quoted.
In the accompanying woodcut (Fig. 2) the line marked 1, 2, 3 represents
the edge of a paper bridge leading to the nest; A the top of a pencil
which is standing perpendicularly upon a board, represented by the
general black surface; B the top of the same pencil when moved a
distance of a few inches from its first position A. On the top of this
pencil were placed some pupæ. Sir John Lubbock, after contriving this
arrangement, marked an ant and put it upon the pupæ on the top of the
pencil. After she had made two journeys carrying pupæ from the pencil to
the nest (the tracks she pursued being represented by the two thick
white lines), while she was in the nest he moved the pencil to its
position at B. The thin white line represents the course then pursued
by the ant in its endeavours to find the pencil, which was shifted only
a few inches from A to B. That is, 'the ants on their journey to the
shifted object travelled very often backwards and forwards and round the
spot where the coveted object first stood. Then they would retrace their
steps towards the nest, wander hither and thither from side to side
between the nest and the point A, and only after very repeated efforts
around the original site of the larvæ reach, as it were, accidentally
the object desired at B.' Therefore the ants were clearly not guided by
the _sight_ of the pencil.
[Illustration: Fig. 2.]
[Illustration: Fig. 3.]
[Illustration: Fig. 4.]
[Illustration: Fig. 5.]
The same thing is well shown by another form of experiment. 'Some food
was placed at the point _a_ (Figs. 3 and 4) on a board measuring 20
inches by 12 inches, and so arranged that the ants in going straight
from it to the nest would reach the board at the point _b_, and after
passing under the paper tunnel _c_, would proceed between five pairs of
wooden bricks, each 3 inches in length and 1-3/4 inches in height. When
they got to know their way they went quite straight along the line _d e_
to _a_. The board was then twisted as shown in Fig. 4. 'The bricks and
tunnel being arranged exactly in the same direction as before, but the
board having been moved, the line _d e_ was now outside them. The
change, however, did not at all discompose the ants; but instead of
going, as before, through the tunnel and between the rows of bricks to
_a_, they walked exactly along the old path to _e_.' Keeping the board
steady, but moving the brick pathway to the left-hand corner of the
board where the food was next placed (Fig. 5), had the effect of making
the ant first go to the old position of the food at _a_, whence it
veered to a new position, which we may call _x_. The bricks and food
were then moved towards the right-hand corner of the board--_i.e._ over
a distance of 8 inches (Fig. 6). The ant now first went to _a_, then to
_x_, and not finding the food at either place, set to work to look for
it at random, and was only successful after twenty-five minutes'
wandering.
[Illustration: Fig. 6.]
And, as evidence how much more dependence they place upon scent in
finding their way than upon any other of their faculties, it is
desirable to quote yet one further experiment, which is of great
interest as showing that when their sense of smell is made to contradict
their sense of direction, they follow the former, notwithstanding, as we
shall presently see, the wonderful accuracy of the information which is
supplied to them by the latter. 'If, when _F. niger_ were carrying off
larvæ placed in a cup on a piece of board, I turned the board round so
that the side which had been turned towards the nest was away from it,
and _vice versâ_, the ants always returned over the same track on the
board, and, in consequence, directly away from home. If I moved my board
to the other side of my artificial nest, the result was the same.
Evidently they followed the road, not the direction.'
There can be little doubt that ants have a sense of taste, as they are
so well able to distinguish sugary substances; and it is unquestionable
that in their antennæ they possess highly elaborated organs of touch.
_Sense of Direction._
As evidence of the accuracy and importance of the sense of direction in
the Hymenoptera, we must here adduce Sir John Lubbock's highly
interesting experiments on ants--leaving his experiments in this
connection on bees and wasps to be considered in the next chapter. He
first accustomed some ants (_Lasius niger_) to go to and fro to food
over a wooden bridge. When they had got quite accustomed to the way, he
watched when an ant was upon a bridge which could be rotated, and while
she was passing along it, he turned it round, so that end _b_ was at
_c_, and _c_ at _b_. 'In most cases the ant immediately turned round
also; but even if she went on to _b_ or _c_, as the case might be, as
soon as she came to the end of the bridge she turned round.' Next,
between the nest and the food he placed a hat-box twelve inches in
diameter and seven inches high, cutting two small holes, so that the
ants in passing from the nest to the food had to pass in at one hole and
out at the other. The box was fixed upon a central pivot, so as to admit
of being rotated easily without much friction or disturbance. When the
ants had well learnt their way, the box was turned half round as soon as
an ant had entered it, 'but in every case the ant turned too, thus
retaining her direction.' Lastly, Sir John took a disk of white paper,
which he placed in the stead of the hat-box between the nest and the
food. When an ant was on the disk making towards the food, he gently
drew the disk to the other side of the food, so that the ant was
conveyed by the moving surface in the same direction as that in which
she was going, but _beyond_ the point to which she intended to go. Under
these circumstances 'the ant did not turn round, but went on' to the
further edge of the disk, when she seemed 'a good deal surprised at
finding where she was.'
These experiments seem to show that the mysterious 'sense of direction,'
and consequent faculty of 'homing,' are in ants, at all events, due to a
process of registering, and, where desirable, immediately counteracting
any change of direction, even when such change is gently made by a
wholly closed chamber in which the animal is moving, and not by any
muscular movements of the animal itself. And the fact that drawing the
moving surface along in the same direction of advance as that which the
insect is pursuing does not affect the movements of the latter, seems
conclusively to show that the power of registration has reference only
to _lateral_ movements of the travelling surface; it has no reference to
variations in the _velocity_ of advance along the line in which the
animal is progressing.[19]
_Powers of Memory._
Little need here be said to prove that ants display some powers of
memory; for many of the observations and experiments already detailed
constitute a sufficient demonstration of the statement that they do.
Thus, for instance, the general fact that whenever an ant finds her way
to a store of food or larvæ, she will return to it again and again in a
more or less direct line from her nest, constitutes ample proof that the
ant remembers the way to the store. It is of considerable interest,
however, to note that the nature of this insect-memory appears to be, as
far as it goes, precisely identical with that of memory in general.
Thus, a new fact becomes _impressed_ upon their memory by _repetition_,
and the impression is liable to become effaced by lapse of time. More
evidence on both these features of insect-memory will be adduced when we
come to treat of the intelligence of bees; but meanwhile it is enough to
refer to the fact that in his experiments on ants, Sir John Lubbock
found it necessary to _teach_ the insects by a repetition of several
lessons their way to treasure, if that way was long or unusual.
With regard to the _duration_ of memory, it does not appear that any
experiments have been made; but the following observation by Mr. Belt on
this point in the case of the leaf-cutting ant may here be stated. In
June 1859 he found his garden invaded by these ants, and following up
their paths he found their nest about a hundred yards distant. He
poured down their burrows a pint of common brown carbolic acid, mixed
with four buckets of water. The marauding parties were at once drawn off
from the garden to meet the danger at home, and the whole formicarium
was disorganised, the ants running up and down again in the utmost
perplexity. Next day he found them busily employed bringing up the
ant-food from the old burrows, and carrying it to newly formed ones a
few yards distant. These, however, turned out to be only intended as
temporary repositories; for in a few days both the old and the new
burrows were entirely deserted, so that he supposed all the ants to have
died. Subsequently, however, he found that they had migrated to a new
site, about two hundred yards from the old one, and there established
themselves in a new nest. Twelve months later the ants again invaded his
garden, and again he treated them to a strong dose of carbolic acid. The
ants, as on the previous occasion, were at once withdrawn from the
garden, and two days afterwards he found 'all the survivors at work on
one track that led directly to the old nest of the year before, where
they were busily employed in making fresh excavations. Many were
bringing along pieces of ant-food' from the nest most recently deluged
with carbolic acid to that which had been similarly deluged a year
before, and from which all the carbolic acid had long ago disappeared.
'Others carried the undeveloped white pupæ and larvæ. It was a wholesale
and entire migration;' and the next day the nest down which he had last
poured the carbolic acid was entirely deserted. Mr. Belt adds: 'I
afterwards found that when much disturbed, and many of the ants
destroyed, the survivors migrate to a new locality. I do not doubt that
some of the leading minds in this formicarium recollected the nest of
the year before, and directed the migration to it.'
Now, I do not insist that the facts necessarily point to this
conclusion; for it may have been that the leaders of the migration
simply stumbled upon the old and vacant nest by accident, and finding it
already prepared as a nest, forthwith proceeded to transfer the food and
pupæ to it. Still, as the two nests were separated from one another by
so considerable a distance, this hypothesis does not seem probable, and
the only other one open to us is that the ants remembered the site of
their former home for a period of twelve months. And this conclusion is
rendered less improbable from a statement of Karl Vogt in his
'Thierstaaten,' to the effect that for several successive years ants
from a certain nest used to go through certain inhabited streets to a
chemist's shop 600 mètres distant, in order to obtain access to a vessel
filled with syrup. As it cannot be supposed that this vessel was found
in successive working seasons by as many successive accidents, it can
only be concluded that the ants remembered the syrup store from season
to season.
I shall now pass on to consider a class of highly remarkable facts,
perhaps the most remarkable of the many remarkable facts connected with
ant psychology.
It has been known since the observations of Huber that all the ants of
the same nest or community recognise one another as friends, while an
ant introduced from another nest, even though it be an ant of the same
species, is known at once to be a foreigner, and is usually maltreated
or put to death. Huber found that when he removed an ant from a nest and
kept it away from its companions for a period of four months it was
still recognised as a friend, and caressed by its previous
fellow-citizens after the manner in which ants show friendship, viz., by
stroking antennæ. Sir John Lubbock, after repeating and fully confirming
these observations, extended them as follows. He first tried keeping the
separated ant away from the nest for a still longer period than four
months, and found that even after a separation of more than a year the
animal was recognised as before. He repeated this experiment a number of
times, and always with the same invariable difference between the
reception accorded to a foreigner and a native--no matter, apparently,
how long the native had been absent.
Considering the enormous number of ants that go to make a nest, it seems
astonishing enough that they should be all personally known to one
another, and still more astonishing that they should be able to
recognise members of their community after so prolonged an absence.
Thinking that the facts could only be explained, either by all the ants
in the same nest having a peculiar smell, or by all the members of the
same community having a particular pass-word or gesture-sign, Sir John
Lubbock, with the view of testing this theory, separated some ants from
a nest while still in the condition of pupæ, and, when they emerged from
that state as perfect insects, transferred them back to the nest from
which they had been taken as pupæ. Of course in this case the ants in
the nest could never have _seen_ those which had been removed, for a
larval ant is as unlike the mature insect as a grub is unlike a beetle;
neither can it be supposed that a larva, hatched out away from the nest,
should retain, when a perfect insect, any smell belonging to its parent
nest--more especially as it had been hatched out by ants in another
nest;[20] nor, lastly, is it reasonable to imagine that the animal, while
still a larval grub, can have been taught any gesture-signal used as a
pass-word by the matured animals. Yet, although all these possible
hypotheses seem to be thus fully excluded by the conditions of the
experiment, the result showed unequivocally that the ants recognised
their transformed larvæ as native-born members of their community.
Lastly, Sir John Lubbock tried the experiment of going still further
back in the life-history of the ants before separating them from the
nest. For in September he divided a nest into two halves, each having a
queen. At this season there were neither larvæ nor eggs. The following
April both the queens began to lay eggs, and in August--_i.e._ nearly a
year after the original partitioning of the nest--he took some of the
ants newly hatched from the pupæ in one division, and placed them in the
other division, and _vice versâ_. In all cases these ants were received
by the members of the other half of the divided nest as friends,
although if a stranger were introduced into either half it was
invariably killed. Yet the ants which were thus so certainly recognised
by their kindred ants as friends had never, even in the state of an egg,
been present in that division of the nest before. On this highly
remarkable fact Sir John Lubbock says:--
These observations seem to me conclusive as far as
they go, and they are very surprising. In my
experiments of last year, though the results were
similar, still the ants experimented with had been
brought up in the nest, and were only removed after
they had become pupæ. It might therefore be argued
that the ants, having nursed them as larvæ, recognised
them when they came to maturity; and though this would
certainly be in the highest degree improbable, it
could not be said to be impossible. In the present
case, however, the old ants had absolutely never seen
the young ones until the moment when, some days after
arriving at maturity, they were introduced into the
nest; and yet in all ten cases they were undoubtedly
recognised as belonging to the community.
It seems to me, therefore, to be established by these
experiments that the recognition of ants is not
personal and individual; that their harmony is not due
to the fact that each ant is individually acquainted
with every other member of the community.
At the same time, the fact that they recognise their
friends even when intoxicated, and that they know the
young born in their own nest even when they have been
brought out of the chrysalis by strangers, seems to
indicate that the recognition is not effected by means
of any sign or pass-word.
We must, therefore, conclude with reference to this subject that the
mode whereby recognition is undoubtedly effected is as yet wholly
unintelligible; and I have introduced these facts under the heading of
memory only because this heading is not more inappropriate than any
other that could be devised for their reception.
It ought here to be added also that the power of thus recognising
members of their community is not confined by the limits of
blood-relationship, for in an experiment made by Forel it was shown that
Amazon ants recognised their own slaves almost instantaneously after an
absence of four months.
Under this heading I may also adduce the evidence as to enormous masses,
or, as we might say, a whole nation of ants recognising each other as
belonging to the same nationality. New nests often spring up as
offshoots from the older ones, and thus a nation of towns gradually
spreads to an immense circumference around the original centre. Forel
describes a colony of _F. exsecta_ which comprised more than two hundred
nests, and covered a space of nearly two hundred square mètres. 'All the
members of such a colony, even those from the furthermost nest,
recognise each other and admit no stranger.'
Similarly, MacCook describes an 'ant town' in the Alleghany Mountains of
North America ('Trans. Amer. Entom. Soc.,' Nov. 1877) which was
inhabited by _F. exsectoïdes_. It consists of 1,600 to 1,700 nests,
which rise in cones to a height of from two to five feet. The ground
below is riddled in every direction with subterranean passages of
communication. The inhabitants are all on the most friendly terms, so
that if any one nest is injured it is repaired by their united forces.
It remains to be added in connection with this subject that the
recognition is not automatically invariable, but when 'ants are removed
from a nest in the pupa state, tended by strangers, and then restored,
some at least of their relatives are certainly puzzled, and in many
cases doubt their claims to consanguinity. I say some, because while
strangers under the circumstances would have been immediately attacked,
these ants were in every case amicably received by the majority of the
colony, and it was sometimes several hours before they came across one
who did not recognise them.'
It may also be added that _Lasius flavus_ behaves towards strangers
quite differently and much more hospitably than is the case with _L.
niger_. The stranger shows no alarm, but, on the contrary, will
voluntarily enter the strange nest, and she is there received with
kindness; although from the attention she excites, and the numerous
communications which take place between her and her new friends, Sir
John was 'satisfied that they knew she was not one of themselves. . . .
Very different is the behaviour of _L. niger_ under similar
circumstances. I tried the same experiment with them. There was no
communications with the antennæ, there was no cleaning, but every ant
which the stranger approached flew at her like a little tigress. I tried
this experiment four times; each stranger was killed and borne off to
the nest.'
_Emotions._
The pugnacity, valour, and rapacity of ants are too well and generally
known to require the narration of special instances of their display.
With regard to the tenderer emotions, however, there is a difference of
opinion among observers. Before the researches of Sir John Lubbock it
was the prevalent view that these insects display marked signs of
affection towards one another, both by caressing movements of their
antennæ, and by showing solicitude for friends in distress. Sir John,
however, has found that the species of ants on which he has experimented
are apparently deficient both in feelings of affection and of
sympathy--or, at least, that such feelings are in these species much
less strongly developed than the sterner passions.
He tried burying some specimens of _Lasius niger_ beneath an ant-road;
but none of the ants traversing the road made any attempt to release
their imprisoned companions. He tried the same experiment with the same
result on various other species. Even when the friends in difficulty are
actually in sight, it by no means follows that their companions will
assist them. Of this, he says, he could give almost any number of
instances. Thus, when ants are entangled in honey, their companions
devote themselves to the honey, and entirely neglect their friends in
distress; and when partly drowned, their friends take no notice. When
chloroformed or intoxicated their own companions either do not heed
them, or else 'seem somewhat puzzled at finding their intoxicated
fellow-creatures in such a condition, take them up, and carry them about
for a time in a somewhat aimless manner.' Further experiments, however,
on a larger scale, went to show that chloroformed ants were treated as
dead, _i.e._ removed to the edge of the parade-board and dropped over
into the surrounding moat of water; while intoxicated ants were
generally carried into the nest, if they were ants belonging to that
community; if not, they were thrown overboard. This care shown towards
intoxicated friends appears to indicate a dim sense of sympathy towards
afflicted individuals; but that this emotion or instinct does not in the
case of these species extend to healthy individuals in distress seems to
be proved, not only by the experiments of burying already described, but
also by the following:--
On Sept. 2, therefore, I put two ants from one of my
nests of _F. fusca_ into a bottle, the end of which
was tied up with muslin as described, and laid it down
close to the nest. In a second bottle I put two ants
from another nest of the same species. The ants which
were at liberty took no notice of the bottle
containing their imprisoned friends. The strangers in
the other bottle, on the contrary, excited them
considerably. The whole day one, two, or more ants
stood sentry, as it were, over the bottle. In the
evening no less than twelve were collected round it, a
larger number than usually came out of the nest at any
one time. The whole of the next two days, in the same
way, there were more or less ants round the bottle
containing the strangers; while, as far as we could
see, no notice whatever was taken of the friends. On
the 9th the ants had eaten through the muslin, and
effected an entrance. We did not chance to be on the
spot at the moment; but as I found two ants lying
dead, one in the bottle and one just outside, I think
there can be no doubt that the strangers were put to
death. The friends throughout were quite neglected.
Sept. 21.--I then repeated the experiment, putting
three ants from another nest in a bottle as before.
The same scene was repeated. The friends were
neglected. On the other hand, some of the ants were
always watching over the bottle containing the
strangers, and biting at the muslin which protected
them. The next morning at 6 A.M. I found five ants
thus occupied. One had caught hold of the leg of one
of the strangers, which had unwarily been allowed to
protrude through the meshes of the muslin. They worked
and watched, though not, as far as I could see, with
any system, till 7.30 in the evening, when they
effected an entrance, and immediately attacked the
strangers.
Sept. 24.--I repeated the same experiment with the
same nest. Again the ants came and sat over the bottle
containing the strangers, while no notice was taken of
the friends.
The next morning again, when I got up, I found five
ants round the bottle containing the strangers, none
near the friends. As in the former case, one of the
ants had seized a stranger by the leg, and was trying
to drag her through the muslin. All day the ants
clustered round the bottle, and bit perseveringly,
though not systematically, at the muslin. The same
thing happened all the following day.
On repeating these experiments with another species
(viz., _Formica rufescens_) the ants took no notice of
either bottle, and showed no sign either of affection
or hatred. One is almost tempted to surmise that the
spirit of these ants is broken by slavery [_i.e._ by
the habit of keeping slaves]. But the experiments on
_F. fusca_ seem to show that in these curious insects
hatred is a stronger passion than affection.
We must not, however, too readily assent to this general conclusion,
that ants as a whole are deficient in the tenderer emotions; for
although the case is doubtless so with the species which Sir John
examined, it appears to be certainly otherwise with other species, as we
shall presently see. But first it may be well to point out that even the
hard-hearted species with which Sir John had to do seem not altogether
devoid of sympathy with sick or mutilated friends, although they appear
to be so towards healthy friends in distress. Thus the care shown to
intoxicated friends seems to indicate, if not, as already observed, a
dim sense of sympathy, at least an instinct to preserve the life of an
ailing citizen for the future benefit of the community. Sir John also
quotes some observations of Latreille showing that ants display sympathy
with mutilated companions; and, lastly, mentions an instance which he
has himself observed of the same thing. A specimen of _F. fusca_
congenitally destitute of antennæ was attacked and injured by an ant of
another species. When separated by Sir John, another ant of her own
species came by. 'She examined the poor sufferer carefully, then picked
her up tenderly, and carried her away into the nest. It would have been
difficult for any one who witnessed this scene to have denied to this
ant the possession of humane feelings.' Moggridge is also of opinion
that the habit of throwing sick and apparently dead ants into the
water, is 'in part to be rid of them, and partly, perhaps, with a view
to effecting a possible cure; for I have seen one ant carry another down
the twig which formed their path to the surface of the water, and, after
dipping it in for a minute, carry it laboriously up again, and lay it in
the sun to dry and recover.'
But that some species of ants display marked signs of what we may call
sympathy even towards healthy companions in distress, is proved by the
following observation of Mr. Belt. He writes:[21]--
One day, watching a small column of these ants (_i.e._
_Eciton humata_), I placed a little stone on one of
them to secure it. The next that approached, as soon
as it discovered its situation, ran backwards in an
agitated manner, and soon communicated the
intelligence to the others. They rushed to the rescue;
some bit at the stone and tried to move it, others
seized the prisoner by the legs and tugged with such
force that I thought the legs would be pulled off, but
they persevered until they got the captive free. I
next covered one up with a piece of clay, leaving only
the ends of its antennæ projecting. It was soon
discovered by its fellows, which set to work
immediately, and by biting off pieces of the clay soon
liberated it. Another time I found a very few of them
passing along at intervals. I confined one of these
under a piece of clay at a little distance from the
line, with his head projecting. Several ants passed
it, but at last one discovered it and tried to pull it
out, but could not. It immediately set off at a great
rate, and I thought it had deserted its comrade, but
it had only gone for assistance, for in a short time
about a dozen ants came hurrying up, evidently fully
informed of the circumstances of the case, for they
made directly for their imprisoned comrade and soon
set him free. I do not see how this action could be
instinctive. It was sympathetic help, such as man only
among the higher mammalia shows. The excitement and
ardour with which they carried on their unflagging
exertions for the rescue of their comrade could not
have been greater if they had been human beings.
This observation seems unequivocal as proving fellow-feeling and
sympathy, so far as we can trace any analogy between the emotions of the
higher animals and those of insects. That insects with such highly
organised social habits, and depending so greatly on the principles of
co-operation, should manifest emotions or instincts of an incipiently
altruistic character, is no more than we should antecedently expect on
the general principle of survival of the fittest. Our only surprise
should be that these emotions, or instincts, should appear to be so
feebly developed in some species of ants, and, as we shall subsequently
see, also of bees. But it may be worth while in this connection to point
out that the valuable observation of Mr. Belt above quoted refers to the
species of ant which, as we shall subsequently find, presents the most
highly organised instincts of co-operation that are to be met with among
ants, and therefore the greatest dependence of the welfare of the
individual on that of the community. And the same remark is applicable
to our native species, _F. sanguinea_, which the Rev. W. W. F. White has
repeatedly seen rescuing buried companions very much in the manner
described by Mr. Belt; and he does not appear to be acquainted with Mr.
Belt's observations. He figures one case in which he saw three ants
co-operating to dig out a buried comrade.[22]
_Powers of Communication._
Huber, Kirby and Spence, Dugardin, Burmeister, Franklin, and other
observers have all expressed themselves as more or less strongly of the
opinion that members of the same community of ants, and other social
Hymenoptera, are able to communicate information to one another by some
system of language or signs. The facts, however, on which their opinion
rests have not been stated with that degree of caution and detail which
the acceptance of the conclusion requires. Thus, Kirby and Spence give
only one instance of supposed communication between ants,[23] and even
this one is inconclusive, as the facts described admit of being
explained by supposing that the ants simply tracked one another by
scent; while Huber merely deals in general statements as to 'contact of
antennæ,' without narrating any particulars of his observations.
Therefore, until within the last few years there was really no
sufficient evidence to sustain the general opinion that ants are able to
communicate with one another; but the observations which I shall now
detail must be regarded as fully substantiating that general opinion by
facts as abundant and conclusive as the most critical among us can
desire. I shall first narrate in his own words the more important of Sir
John Lubbock's experiments in this connection:--
I took three tapes, each about 2 feet 6 inches long,
and arranged them parallel to one another and about 6
inches apart. An end of each I attached to one of the
nests (_F. niger_), and at the other end I placed a
glass. In the glass at the end of one tape I placed a
considerable number (300 to 600) of larvæ. In the
second I put two or three larvæ only, in the third
none at all. The object of the last was to see whether
many ants would come to the glasses under such
circumstances by mere accident, and I may at once say
that scarcely any did so. I then took two ants, and
placed one of them to the glass with many larvæ, the
other to that with two or three. Each of them took a
larva and carried it to the nest, returning for
another, and so on. After each journey I put another
larva in the glass with only two or three larvæ, to
replace that which had been removed. Now, if several
ants came under the above circumstances as a mere
matter of accident, or accompanying one another by
chance, or if they simply saw the larvæ which were
being brought, and consequently concluded that they
might themselves find a larva in the same place, then
the numbers going to the two glasses ought to be
approximately equal. In each case the number of
journeys made by the ants would be nearly the same;
consequently, if it was a matter of scent, the two
glasses would be in the same position. It would be
impossible for an ant, seeing another in the act of
bringing a larva, to judge for itself whether there
were few or many left behind. On the other hand, if
the strangers were brought, then it would be curious
to see whether more were brought to the glass with
many larvæ than to that which only contained two or
three. I should also mention that every stranger was
imprisoned until the end of the experiment.
The results of these experiments were that during 47-1/2 hours the ants
which had access to a glass containing numerous larvæ brought 257
friends to their assistance; while during an interval 5-1/2 hours longer
those which visited the glass with only two or three larvæ brought only
82 friends; and, as already mentioned, no single ant came to the glass
which contained no larvæ. Now, as all the glasses were exposed to
similar conditions, and as the roads to the first two must, in the first
instance at all events, have been equally scented by the passage of ants
over them, these results look very conclusive as proving some power of
definite communication, not only that larvæ are to be found, but even
where the largest store is to be met with.
To this interesting account Sir John Lubbock adds,--
One case of apparent communication struck me very
much. I had had an ant (_F. niger_) under observation
one day, during which she was occupied in carrying off
larvæ to her nest. At night I imprisoned her in a
small bottle; in the morning I let her out at 6.15,
when she immediately resumed her occupation. Having to
go to London, I imprisoned her again at 9 o'clock.
When I returned at 4.40 I put her again to the larvæ.
She examined them carefully, and went home without
taking one. At this time no other ants were out of the
nest. In less than a minute she came out again with
eight friends, and the little heap made straight for
the heap of larvæ. When they had gone two-thirds of
the way I again imprisoned the marked ant; the others
hesitated a few minutes, and then with curious
quickness returned home. At 5.15 I put her again to
the larvæ. She again went home _without a larva_, but
after only a few seconds' stay in the nest, came out
with no less than thirteen friends. They all went
towards the larvæ, but when they had got about
two-thirds of the way, although the marked ant had on
the previous day passed over the ground about 150
times, and though she had just gone straight from the
larvæ to the nest, she seemed to have forgotten her
way, and considered; and after she had wandered about
for half an hour, I put her to the larvæ. Now, in this
case, the twenty-one ants must have been brought out
by my marked one, for they came exactly with her, and
there were no other ants out. Moreover, it would seem
that they must have been told, because (which is very
curious in itself) she did not in either case bring a
larva, and consequently it cannot have been the mere
sight of a larva which had induced them to follow her.
Further experiments proved, as we might have expected, that although an
ant is able to communicate to her friends in the nest that she has found
treasure somewhere outside, she is not able to describe to them its
precise locality. Thus, having exposed larvæ and placed an ant upon them
as before, Sir John watched every time she came out of the nest with
friends to assist her, but instead of allowing her to pilot the way, he
took her up and carried her to the larvæ, allowing her to return with a
larva upon her own feet. Under these circumstances the friends, although
evidently coming out with the intention of finding some treasure, were
never able to find it; but wandered about in various directions for a
while, and then returned to the nest. Thus, during two hours she brought
out in her successive journeys altogether no less than 120 ants, of
which number only 5 in their unguided wanderings happened to find the
sought-for treasure. This result seems to prove, as we might have
expected, that the communication is of the nature of some sign amounting
to no more than a 'follow me.' Other experiments confirmed this result,
and also brought out the fact that 'some species act much more in
association than others--_Formica fusca_, for instance, much less than
_Lasius niger_.' Thus Sir John Lubbock placed some honey before a marked
specimen of the former species; but although she visited and revisited
the honey during an entire day, she brought out no friends to share it;
and although in her journeys to and from the nest she happened to pass
and repass many other individuals, they took no notice of each other.
The obvious objection to these experiments, that an ant observing a
friend bringing home food or a pupa might infer, without being told,
that by accompanying the friend on the return journey she 'might
participate in the good things,' has been partly met by the fact already
stated, viz., that there is so very marked a difference in the result
if, on experimenting on two ants, one had access to a large treasure and
the other only to a small one. But to put this matter beyond question,
Sir John Lubbock tried the experiment of pinning down a dead fly, so
that the ant which found it was unable, with all her tugging, to move it
towards the nest. At length she went back to the nest for assistance,
and returned accompanied by seven friends. So great was her excitement,
however, that she outran these friends, 'who seemed to have come out
reluctantly, as if they had been asleep, and were only half awake;' and
they failed to find the fly, slowly meandering about for twenty minutes.
After again tugging for a time at the fly, the first ant returned a
second time to the nest for assistance, and in less than a minute came
out with eight friends. They were even less energetic than the first
party, and having lost sight of their guide in the same manner as
happened before, they all returned to the nest. Meanwhile several of the
first party, which had all the while been meandering about, found the
fly, and proceeded to dismember it, carrying the trophy to the nest, and
calling out more friends in the ordinary way. This experiment was
repeated several times and on different species, always with the same
result. Now, as Sir John remarks, 'the two cases (_i.e._ those in which
the ant brought out friends to her assistance even when she had no booty
to show) surely indicate a distinct power of communication. . . . It is
impossible to doubt that the friends were brought out by the first ant;
and as she returned empty-handed to the nest, the others cannot have
been induced to follow her by merely observing her proceedings. I
conclude, therefore, that they possess the power of requesting their
friends to come and help them.'
In order to ascertain whether the signs which communicating ants make to
one another are made by means of sound, Sir John Lubbock placed near a
nest of _Lasius flavus_ six small upright pillars of wood about 1-1/2
inch high, and on one of these he put a drop of honey. 'I then put three
ants to the honey, and when each had sufficiently fed, I imprisoned her,
and put another; thus always keeping three ants at the honey, but not
allowing them to go home. If, then, they could summon their friends by
sound, there ought soon to be many ants at the honey.' The result
showed that the ants were not able thus to call to one another from a
distance.
As additional proof of the general fact that at all events some ants
have the power of communicating information to one another, it will be
enough here to quote an exceedingly interesting observation of the
distinguished geologist Hague. The quotations are taken from his letters
written to Mr. Darwin, and published in _Nature_:[24]--
On the mantelshelf of our sitting-room my wife has the
habit of keeping fresh flowers. A vase stands at each
end, and near the middle a small tumbler, usually
filled with violets. Some time ago I noticed a pile of
very small red ants on the wall above the left-hand
vase, passing upward and downward between the
mantelshelf and a small hole near the ceiling, at a
point where a picture nail had been driven. The ants,
when first observed, were not very numerous, but
gradually increased in number, until on some days the
little creatures formed an almost unbroken procession,
issuing from the hole at the nail, descending the
wall, climbing the vase directly below the nail,
satisfying their desire for water or perfume, and then
returning. The other vase and tumbler were not visited
at that time.
As I was just then recovering from a long illness it
happened that I was confined to the house, and spent
my days in the room where the operations of these
insects attracted my attention. Their presence caused
me some annoyance, but I knew of no effective means of
getting rid of them. For several days in succession I
frequently brushed the ants in great numbers from the
wall down to the floor; but as they were not killed
the result was that they soon formed a colony in the
wall at the base of the mantel, ascending thence to
the shelf, so that before long the vase was attacked
from above and below.
One day I observed a number of ants, perhaps thirty or
forty, on the shelf at the foot of the vase. Thinking
to kill them, I struck them lightly with the end of my
finger, killing some and disabling the rest. The
effect of this was immediate and unexpected. As soon
as those ants which were approaching arrived near to
where their fellows lay dead and suffering, they
turned and fled with all possible haste. In half an
hour the wall above the mantelshelf was cleared of
ants.
During the space of an hour or two the colony from
below continued to ascend until reaching the lower
bevelled edge of the shelf, at which point the more
timid individuals, although unable to see the vase,
somehow became aware of trouble, and turned about
without further investigation, while the more daring
advanced hesitatingly just to the upper edge of the
shelf, when, extending their antennæ and stretching
their necks, they seemed to peep cautiously over the
edge until beholding their suffering companions, when
they too turned and followed the others, expressing by
their behaviour great excitement and terror. An hour
or two later, the path or trail leading from the lower
colony to the vase was almost entirely free from ants.
I killed one or two ants on their path, striking them
with my finger, but leaving no visible trace. The
effect of this was that as soon as an ant ascending
towards the shelf reached the spot where one had been
killed, it gave signs immediately of great
disturbance, and returned directly at the highest
possible speed.
A curious and invariable feature of their behaviour
was that when such an ant, returning in fright, met
another approaching, the two would always communicate,
but each would pursue its own way, the second ant
continuing its journey to the spot where the first had
turned about, and then following that example.
For some days after this there were no ants visible on
the wall, either above or below the shelf.
Then a few ants from the lower colony began to
reappear, but instead of visiting the vase which had
been the scene of the disaster, they avoided it
altogether, and following the lower front edge of the
shelf to the tumbler standing near the middle, made
their attack upon that. I repeated the same experiment
here with precisely the same result. Killing or
maiming a few of the ants and leaving their bodies
about the base of the tumbler, the others on
approaching, and even before arriving at the upper
surface of the shelf where their mutilated companions
were visible, gave signs of intense emotion, some
running away immediately, and others advancing to
where they could survey the field and then hastening
away precipitately.
Occasionally an ant would advance towards the tumbler
until it found itself among the dead and dying; then
it seemed to lose all self-possession, running hither
and thither, making wide circuits about the scene of
the trouble, stopping at times and elevating the
antennæ with a movement suggestive of wringing them in
despair, and finally taking flight. After this another
interval of several days passed, during which no ants
appeared. Now, three months later, the lower colony
has been entirely abandoned. Occasionally, however,
especially when fresh and fragrant violets have been
placed on the shelf, a few 'prospectors' descend from
the upper nail-hole, rarely, almost never, approaching
the vase from which they were first driven away, but
seeking to satisfy their desire at the tumbler. To
turn back these stragglers and keep them out of sight
for a number of days, sometimes for a fortnight, it is
sufficient to kill one or two ants on the trail which
they follow descending the wall. This I have recently
done as high up as I can reach, three or four feet
above the mantel. The moment this spot is reached, an
ant turns abruptly and makes for home, and in a little
while there is not an ant visible on the wall.
In a subsequent volume of 'Nature' (viii. p. 244), Mr. Darwin publishes
another letter which he received from Mr. Hague upon the same subject.
It seems that Mr. Moggridge suggested to Mr. Darwin that, as he and
others had observed ants to be repelled by the mere scent of a finger
drawn across their path, the observation of Mr. Hague might really
resolve itself into a dislike on the part of the ants to cross a line
over which a finger had been drawn, and have nothing to do with
intelligent terror inspired by the sight of their slaughtered
companions. The following is Mr. Hague's reply to Mr. Darwin's request
for further experiments to test this point:--
Acting on Mr. M----'s suggestion, I first tried making
simple finger-marks on their path (the mantel is of
marble), and found just the results which he describes
in his note as observed by himself at Mentone, that
is, no marked symptoms of fear, but a dislike to the
spot, and an effort to avoid it by going around it, or
by turning back and only crossing it again after an
interval of time. I then killed several ants on the
path, using a smooth stone or piece of ivory, instead
of my finger, to crush them. In this case the ants
approaching all turned back as before, and with much
greater exhibition of fear than when the simple
finger-mark was made. This I did repeatedly. The final
result was the same as obtained last winter. They
persisted in coming for a week or two, during which I
continued to kill them, and then they disappeared, and
we have seen none since. It would appear from this
that while the taint of the hand is sufficient to turn
them back, the killing of their fellows with a stone
or other material produces the effect described in my
first note. This was made clear to me at that time,
from the behaviour of the ants the first day I killed
any, for on that occasion some of them approaching the
vase from below, on reaching the upper edge of the
mantel, peeped over, and drew back on seeing what had
happened about the vase, then turned away a little,
and after a moment tried again at another and another
point along the edge, with the same result in the end.
Moreover, those that found themselves among the dead
and dying went from one writhing ant to another in
great haste and excitement, exhibiting the signs of
fright which I described.
I hardly hope that any will return again, but if they
do, and give me an opportunity, I shall endeavour to
act further on Mr. M----'s suggestion.
With this quotation I shall conclude the present division of the
chapter; for, looking to all the other observations previously
mentioned, there can be no question concerning the general fact that
ants have the power of communicating with one another. And under
subsequent headings abundant additional evidence on this point will be
found implicated with the other facts detailed.
_Habits General in Sundry Species._
_Swarming._--The precise facts with regard to the swarming of ants are
not yet certainly established. As regards some of the facts, however,
there is no doubt. The winged males and females first quit the nest in
enormous numbers, and choose some fine afternoon in July or August for
their wedding flight. The entrances to the nest are widened by the
workers and increased in number, and there is a great commotion on the
surface of the nest. The swarm takes place as a thick cloud of all the
male and female insects, rising together to a considerable height. The
flight continues for several hours, usually circling round some tree or
tower, and it is during the flight that fertilisation is effected. After
it is effected, the swarm returns to the ground, when the males perish,
either from falling a prey, in their shelterless condition, to birds or
spiders, or, on account of not being able to feed themselves, from
starvation. 'The workers, or neuter ants, of their own colony have lost
all interest in them from the moment of their return, and trouble
themselves no more about them, for they well know that the males have
now fulfilled their vocation.' The great majority of the fertilised
females share the same fate as the males. But a small proportion find
concealment in holes, which they either dig for themselves, or happen to
find ready made, and there found a new colony. The first thing they do
is to pull off their now useless wings, by scratching and twisting them,
one after the other, with the clawed ends of their feet. They then lay
their eggs, and become the queens of new colonies.
Forel says that no fertilised female ever returns to her original home;
but that the workers keep back a certain number of females which are
fertilised before the swarming takes place; in this case the workers
pull off the wings of the fertilised females. The majority of observers,
however, maintain that some of the females composing the swarm return to
their native home to become mothers where they had been children.
Probably both statements are correct. A writer in the 'Groniger
Deekblad' for June 16, 1877, observes that, looking to the injurious
effects of in-breeding, the facts as related by Forel are less probable
than those related by other observers, and that, if they actually occur,
the females fertilised before flight are probably kept by the ants as a
sort of 'reserve corps to which the workers resort only in case of need,
and if they fail to secure any returning queens.'
_Nursing._--The eggs will not develop into larvæ unless nursed. The
nursing is effected by licking the surface of the eggs, which under the
influence of this process increase in size, or grow. In about a
fortnight, during which time the workers carry the eggs from higher to
lower levels of the nest, and _vice versâ_, according to the
circumstances of heat, moisture, &c., the larvæ are hatched out, and
require no less careful nursing than the eggs. The workers feed them by
placing mouths together and regurgitating food stored up in the crop or
proventriculus into the intestinal tract of the young. The latter show
their hunger by 'stretching out their little brown heads.' Great care
is also taken by the workers in cleaning the larvæ, as well as in
carrying them up and down the chambers of the nest for warmth or
shelter.
When fully grown the larvæ spin cocoons, and are then pupæ, or the
'ants' eggs' of bird-fanciers. These require no food, but still need
incessant attention with reference to warmth, moisture, and cleanliness.
When the time arrives for their emergence as perfect insects, the
workers assist them to get out of their larval cases by biting through
the walls of the latter. It is noticeable that in doing this the workers
do not keep to any exact time, but free them sometimes earlier and
sometimes later, in accordance with their rate of development. 'The
little animal when freed from its chrysalis is still covered with a thin
skin, like a little shirt, which has to be pulled off. When we see how
neatly and gently this is done, and how the young creature is then
washed, brushed, and fed, we are involuntarily reminded of the nursing
of human babies. The empty cases, or cocoons, are carried outside the
nest, and may be seen heaped together there for a long time. Some
species carry them far away from the nest, or turn them into building
materials for the dwelling.'[25]
_Education._--The young ant does not appear to come into the world with
a full instinctive knowledge of all its duties as a member of a social
community. It is led about the nest, and 'trained to a knowledge of
domestic duties, especially in the case of the larvæ.' Later on the
young ants are taught to distinguish between friends and foes. When an
ants' nest is attacked by foreign ants, the young ones never join in the
fight, but confine themselves to removing the pupæ; and that the
knowledge of hereditary enemies is not wholly instinctive in ants is
proved by the following experiment, which we owe to Forel. He put young
ants belonging to three different species into a glass case with pupæ of
six other species--all the species being naturally hostile to one
another. The young ants did not quarrel, but worked together to tend the
pupæ. When the latter hatched out, an artificial colony was formed of a
number of naturally hostile species all living together after the manner
of the 'happy families' of the showmen.
_Habit of keeping Aphides._--It is well known that various species of
ants keep aphides, as men keep milch cows, to supply a nutritious
secretion. Huber first observed this fact, and noticed that the ants
collected the eggs of the aphides and treated them exactly as they
treated their own, guarding and tending them with the utmost care. When
these eggs hatch out the aphides are usually kept and fed by the ants,
to whom they yield a sweet honey-like fluid, which they eject from the
abdomen upon being stroked on this region by the antennæ of the ants.
Mr. Darwin, who has watched the latter process, observes with regard to
it,--
I removed all the ants from a group of about a dozen
aphides on a dock plant, and prevented their
attendance during several hours. After this interval,
I felt sure that the aphides would want to excrete. I
watched them for some time through a lens, but not one
excreted; I then tickled them with a hair in the same
manner, as well as I could, as the ants do with their
antennæ; but not one excreted. Afterwards I allowed an
ant to visit them, and it immediately seemed, by its
eager way of running about, to be well aware what a
rich flock it had discovered; it then began to play
with its antennæ on the abdomen, first of one aphis
and then of another; and each, as soon as it felt the
antennæ, immediately lifted up its abdomen and
excreted a limpid drop of sweet juice, which was
eagerly devoured by the ant. Even quite young aphides
behaved in this manner, showing that the action was
instinctive, and not the result of experience.
The facts also show that the yielding of the secretion to the ants is,
as it were, a voluntary act on the part of the aphides, or, perhaps more
correctly, that the instinct to yield it has been developed in such a
relation to the requirements of the ants, that the peculiar stimulation
supplied by the antennæ of the latter is necessary to start the act of
secretion; for in the absence of this particular stimulation the aphides
will never excrete until compelled to do so by the superabundance of the
accumulating secretion. The question, therefore, directly arises how, on
evolutionary principles, such a class of facts is to be met; for it is
certainly difficult to understand the manner in which this instinct, so
beneficial to the ants, can have arisen in the aphides, to which it does
not appear, at first sight, to offer any advantages. Mr. Darwin meets
the difficulty thus: 'Although there is no evidence that any animal
performs an action for the exclusive good of another species, yet each
tries to take advantage of the instincts of others;' and 'as the
secretion is extremely viscid, it is no doubt a convenience to the
aphides to have it removed; therefore probably they do not excrete
solely for the good of the ants.'[26]
Some ants which keep aphides build covered ways, or tunnels, to the
trees or shrubs where the aphides live. Forel saw a tunnel of this kind
which was taken up a wall and down again on the other side, in order to
secure a safe covered way from the nest to the aphides. Occasionally
such covered ways, or tubes, are continued so as to enclose the stems of
the plants on which the aphides live. The latter are thus imprisoned by
the walls of the tube, which, however, expand where they take on this
additional function of stabling the aphides, so that these insects are
really confined in tolerably large chambers. The doors of these chambers
are too small to allow the aphides to escape, while large enough for the
ants to pass in and out. Forel saw such a prison or stable shaped like a
cocoon, and about a centimètre long, which was hanging on the branch of
a tree, and contained aphides carefully tended by the ants. Huber
records similar observations.
Sir John Lubbock has made an interesting addition to our knowledge
respecting this habit as practised by a certain species of ant (_Lasius
flavus_), which departs in a very remarkable manner from the habit as
practised by other species. He says: 'The ants took the greatest care of
these eggs, carrying them off to the lower chambers with the utmost
haste when the nest was disturbed.' But the most interesting of Sir John
Lubbock's observations in this connection is new, and reveals an
astonishing amount of method shown by the ants in farming their
aphides. He says:--
When my eggs hatched I naturally thought that the
aphides belonged to one of the species usually found
on the roots of plants in the nests of _Lasius
flavus_. To my surprise, however, the young creatures
made the best of their way out of the nest, and,
indeed, were sometimes brought out by the ants
themselves. In vain I tried them with roots of grass,
&c.; they wandered uneasily about, and eventually
died. Moreover, they did not in any way resemble the
subterranean species. In 1878 I again attempted to
rear these young aphides; but though I hatched a great
many eggs, I did not succeed. This year, however, I
have been more fortunate. The eggs commenced to hatch
the first week in March. Near one of my nests of
_Lasius flavus_, in which I had placed some of the
eggs in question, was a glass containing living
specimens of several species of plants commonly found
on or around ants' nests. To this some of the young
aphides were brought by the ants. Shortly afterwards I
observed on a plant of daisy, in the axils of the
leaves, some small aphides, very much resembling those
from my nest, though we had not actually traced them
continuously. They seemed thriving, and remained
stationary on the daisy. Moreover, whether they had
sprung from the black eggs or not, the ants evidently
valued them, for they built up a wall of earth round
and over them. So things remained throughout the
summer, but on October 9 I found that the aphides had
laid some eggs exactly resembling those found in the
ants' nests; and on examining daisy plants from
outside, I found on many of them similar aphides, and
more or less of the same eggs.
I confess these observations surprised me very much.
The statements of Huber have not, indeed, attracted so
much notice as many of the other interesting facts
which he has recorded, because if aphides are kept by
ants in their nests, it seems only natural that their
eggs should also occur. The above case, however, is
much more remarkable. Here are aphides, not living in
the ants' nests, but outside, on the leaf-stalks of
plants. The eggs are laid early in October on the
food-plant of the insect. They are of no direct use to
the ants, yet they are not left where they are laid,
where they would be exposed to the severity of the
weather and to innumerable dangers, but brought into
their nests by the ants, and tended by them with the
utmost care through the long winter months until the
following March, when the young ones are brought out
and again placed on the young shoots of the daisy.
This seems to me a most remarkable case of prudence.
Our ants may not perhaps lay up food for the winter,
but they do more, for they keep during six months the
eggs which will enable them to procure food during the
following summer.
The following, which is taken from Büchner's 'Geistesleben der Thiere'
is perhaps a still more striking performance of the same kind as that
which Sir John Lubbock observed:--
The author is debtor to Herr Nottebohm, Inspector of
Buildings at Karlsruhe, who related the following on
May 24, 1876, under the title, 'Ants as Founders of
Aphides' Colonies:'--'Of two equally strong young
weeping ashes, which I planted in my garden at
Kattowitz, in Upper Silesia, one succeeded well, and
in about five or six years showed full foliage, while
the other regularly every year was covered, when it
began to bud, with millions of aphides, which
destroyed the young leaves and sprouts, and thus
completely delayed the development of the tree. As I
perceived that the only reason for this was the action
of the aphides, I determined to destroy them utterly.
So in the March of the following year I took the
trouble to clean and wash every bough, sprig, and bud
before the bursting of the latter, with the greatest
care, by means of a syringe. The result was that the
tree developed perfectly healthy and vigorous leaves
and young shoots, and remained quite free from the
aphides until the end of May or the beginning of June.
My joy was of short duration. One fine sunny morning I
saw a surprising number of ants running quickly up and
down the trunk of the tree; this aroused my attention,
and led me to look more closely. To my great
astonishment I then saw that many troops of ants were
busied in carrying single aphides up the stem to the
top, and that in this way many of the lower leaves had
been planted with colonies of aphides. After some
weeks the evil was as great as ever. The tree stood
alone on the grass plot, and offered the only
situation for an aphides' colony for the countless
ants there present. I had destroyed this colony; but
the ants replanted it by bringing new colonists from
distant branches, and setting them on the young
leaves.[27]
Again--
MacCook noticed, of the mound-making ants, that of
the workers returning to the nest from the tree on
which the milking was going on, a far smaller number
had distended abdomens than among those descending the
tree itself. A closer investigation showed that at the
roots of the trees, at the outlets of the subterranean
galleries, a number of ants were assembled, which were
fed by the returning ants after the fashion already
described in feeding the larvæ, and which were
distinguished by the observer as 'pensioners.' MacCook
often observed the same fact later, among, with
others, the already described Pennsylvanian wood-ant.
Distinguished individuals in the body-guard of the
queen were fed in like fashion. MacCook is inclined to
think that the reason of this proceeding is to be
found in the 'division of labour' so general in the
ant republic, and that the members of the community
which are employed in building and working within the
nest, leave to the others the care of providing food
for themselves as well as for the younger and helpless
members; they thus have a claim to receive from time
to time a reciprocal toll of gratitude, and take it,
as is shown very clearly, in a way demanded by the
welfare of the community.[28]
Aphides are not the only insects which ants employ as cows, several
other insects which yield sweet secretions being similarly utilised in
various parts of the world. Thus, gall insects and cocci are kept in
just the same way as aphides; but MacCook observed that where aphides
and cocci are kept by the same ants, they are kept in separate chambers,
or stalls. The same observer saw caterpillars of the genus _Lycoena_
kept by ants for the sake of a sweet secretion which they supply.
_Habit of making Slaves._--This habit, or instinct, obtains among at
least three species of ant, viz., _Formica rufescens_, _F. sanguinea_,
and _strongylognathus_. It was originally observed by P. Huber in the
first-named species. Here the species enslaved is _F. fusca_, which is
appropriately coloured black. The slave-making ants attack a nest of _F.
fusca_ in a body; there is a great fight with much slaughter, and, if
victorious, the slave-makers carry off the pupæ of the vanquished nest
in order to hatch them out as slaves. Mr. Darwin gives an account of a
battle which he himself observed.[29]
When the pupæ hatch out in the nest of their captors, the young slaves
begin their life of work, and seem to regard their master's home as
their own; for they never attempt to escape, and they fight no less
keenly than their masters in defence of the nest. _F. sanguinea_ content
themselves with fewer slaves than do _F. rufescens_; and the work that
devolves upon the slaves differs according to the species which has
enslaved them. In the nests of _F. sanguinea_ the comparatively few
captives are kept as household slaves; they never either enter or leave
the nest, and so are never seen unless the nest is opened. They are then
very conspicuous from the contrast which their black colour and small
size present to the red colour and much larger size of _F. rufescens_.
As the slaves are by this species kept strictly indoors, all the outdoor
work of foraging, slave-capturing, &c., is performed by the masters; and
when for any reason a nest has to migrate, the masters carry their
slaves in their jaws. _F. rufescens_, on the other hand, assigns a much
larger share of labour to the slaves, which, as we have already seen,
are present in much larger numbers to take it. In this species the males
and fertile females do no work of any kind; and the workers, or sterile
females, though most energetic in capturing slaves, do no other kind of
work. Therefore the whole community is absolutely dependent upon its
slaves. The masters are not able to make their own nests or to feed
their own larvæ. When they migrate, it is the slaves that determine the
migration, and, reversing the order of things that obtains in _F.
sanguinea_, carry their masters in their jaws. Huber shut up thirty
masters without a slave and with abundance of their favourite food, and
also with their own larvæ and pupæ as a stimulus to work; but they could
not feed even themselves, and many died of hunger. He then introduced a
single slave, and she at once set to work, fed the surviving masters,
attended to the larvæ, and made some cells.
In order to confirm this observation, Lespès placed a piece of sugar
near a nest of slave-makers. It was soon found by one of the slaves,
which gorged itself and returned to the nest. Other slaves then came out
and did likewise. Then some of the masters came out, and, by pulling
the legs of the feeding slaves, reminded them that they were neglecting
their duty. The slaves then immediately began to serve their masters
with the sugar. Forel also has confirmed all these observations of
Huber. Indeed, in the case of _F. rufescens_, the structure of the
animal is such as to render self-feeding physically impossible. Its long
and narrow jaws, adapted to pierce the head of an enemy, do not admit of
being used for feeding, unless liquid food is poured into them by the
mouth of a slave. This fact shows of how ancient an origin the instinct
of slave-making must be; it has altered in an important manner a
structure which could not have been so altered prior to the
establishment of the instinct in question.
Mr. Darwin thus sums up the differences in the offices of the slaves in
the nests of _F. sanguinea_ and _F. rufescens_ respectively:--
The latter does not build its own nest, does not
determine its own migrations, does not collect food
for itself or for its fellows, and cannot even feed
itself; it is absolutely dependent on its numerous
slaves. _Formica sanguinea_, on the other hand,
possesses much fewer slaves, and in the early part of
the summer extremely few; the masters determine when
and where a new nest shall be formed, and when they
migrate, the masters carry the slaves. Both in
Switzerland and England the slaves seem to have the
exclusive care of the larvæ, and the masters alone go
on slave-making expeditions. In Switzerland the slaves
and masters work together, making and bringing
materials for the nest; both, but chiefly the slaves,
tend and milk, as it may be called, their aphides; and
thus both collect food for the community. In England
the masters alone usually leave the nest to collect
building materials and food for themselves, their
slaves and larvæ. So that the masters in this country
receive much less service from their slaves than they
do in Switzerland.
Mr. Darwin further observes that 'this difference in the usual habits of
the masters and slaves in the two countries probably depends merely on
the slaves being captured in greater numbers in Switzerland than in
England;' and records that he has observed in a community of the English
species having an unusually large stock of slaves that 'a few slaves
mingled with their masters leaving the nest, and marched along the same
road to a tall Scotch fir tree, twenty-five yards distant, which they
ascended together, probably in search of aphides or cocci.' And,
according to Huber, the principal office of the slaves in Switzerland is
to search for aphides.
Mr. Darwin also made the following observation:--'Desiring to ascertain
whether _F. sanguinea_ could distinguish the pupæ of _F. fusca_, which
they habitually make into slaves, and which are an unwarlike species,
from _F. flava_, which they rarely capture, and never without a severe
fight,' he found 'it was evident that they did at once distinguish
them;' for while 'they eagerly and instantly seized the pupæ of _F.
fusca_, they were much terrified when they came across the pupæ, or even
the earth from the nest, of _F. flava_, and quickly ran away; but in
about a quarter of an hour, shortly after the little yellow ants had
crawled away (from their nest having been disturbed by Mr. Darwin), they
took heart and carried off the pupæ.'
Concerning the origin of this remarkable instinct, Mr. Darwin writes:--
As ants which are not slave-makers will, as I have
seen, carry off pupæ of other species if scattered
near their nests, it is possible that such pupæ
originally stored as food might become developed, and
the foreign ants thus unintentionally reared would
then follow their proper instincts, and do what work
they could. If their presence proved useful to the
species which had seized them--if it were more
advantageous to the species to capture workers than to
procreate them--the habit of collecting pupæ,
originally for food, might by natural selection be
strengthened and rendered permanent for the very
different purpose of raising slaves. When the instinct
was once acquired, if carried out to a much less
extent even than in our British _F. sanguinea_, which,
as we have seen, is less aided by its slaves than the
same species in Switzerland, natural selection might
increase and modify the instinct, always supposing
such modification to be of use to the species, until
an ant was found as abjectly dependent on its slave as
is the _Formica rufescens_.
Ants do not appear to be the only animals of which ants make slaves; for
there seems to be at least one case in which these wonderful insects
enslave insects of another species, which therefore may be said to stand
to the ants in the relation of beasts of burden. The case to which I
allude is one that is recorded in Perty's 'Intellectual Life of Animals'
(2nd ed. p. 329), and is as follows:--
According to Audubon certain leaf-bugs are used as
slaves by the ants in the Brazilian forests. When
these ants want to bring home the leaves which they
have bitten off the trees, they do it by means of a
column of these bugs, which go in pairs, kept in order
on either side by accompanying ants. They compel
stragglers to re-enter the ranks, and laggards to keep
up by biting them. After the work is done the bugs are
shut up within the colony and scantily fed.
_Wars._--On the wars of ants a great deal might be said, as the facts of
interest in this connection are very numerous; but for the sake of
brevity I shall confine myself to giving only a somewhat meagre account.
One great cause of war is the plundering of ants' nests by the
slave-making species. Observers all agree that this plundering is
effected by a united march of the whole army composing a nest of the
slave-making species, directed against some particular nest of the
species which they enslave. According to Lespès and Forel, single scouts
or small companies are first sent out from the nest to explore in
various directions for a suitable nest to attack. These scouts
afterwards serve as guides to the marauding excursion. Forel saw several
of these scouts of the species _F. rufescens_ or Amazon carefully
inspecting a nest of _F. fusca_ which they had found, investigating
especially the entrances. These are purposely made difficult to find by
their architects, and it not unfrequently happens that after all
precautions and inspections on the part of the invaders, an expedition
fails on account of not finding the city gates.
When the scouts have been successful in discovering a suitable nest to
plunder, and have completed their strategical investigations of the
locality to their satisfaction, they return straight to their own nest
or fortress. Forel has then seen them walking about on the surface of
their nest for a long time, as if in consultation, or making up their
minds. Then some of them entered the nest, soon after which hosts of
warriors streamed out of the entrances, and ran about tapping each other
with their heads and antennæ. They then formed into column and set out
to pillage the nest of the slave ants. The following is the account
which Lespès gives of such expeditions:--
They only take place towards the end of the summer and
in autumn. At this time the winged members of the
slave species (_F. fusca_ and _F. cunicularia_) have
left the nest, and the Amazons will not take the
trouble to bring back useless consumers. When the sky
is clear our robbers leave their town in the afternoon
at about three or four o'clock. At first no order is
perceptible in their movements, but when they are all
gathered together they form a regular column, which
then moves forward quickly, and each day in a
different direction. They march closely pressed
together, and the foremost always appear to be seeking
for something on the ground. They are each moment
overtaken by others, so that the head of the column is
continually growing. They are in fact seeking the
traces of the ants which they propose to plunder, and
it is scent that guides them. They snuff over the
ground like hounds following the track of a wild
animal, and when they have found it they plunge
headlong forward, and the whole column rushes on
behind. The smallest armies I saw consisted of several
hundred individuals, but I have also seen some four
times as large. They then form columns which may be
five mètres long, and as much as fifty centimètres
wide. After a march, which often lasts a full hour,
the column arrives at the nest of the slave species.
The _F. cuniculariæ_, which are the strongest, offer
keen opposition, but without much result. The Amazons
soon penetrate within the nest, to come out again a
moment later, while the assailed ants at the same time
rush out in masses. During the whole time attention is
directed solely to the larvæ and pupæ, which the
Amazons steal while the others try to save as many as
possible. They know very well that the Amazons cannot
climb, so they fly with their precious burdens to the
surrounding bushes or plants, whereto their enemies
cannot follow them. They then pursue the retreating
robbers and try to take away from them as much of
their booty as possible. But the latter do not trouble
themselves much about them, and hasten on home. On
their return they do not follow the shortest road, but
exactly the one by which they came, finding their way
back by smell. Arrived at their nest, they
immediately hand over their booty to the slaves, and
trouble themselves no more about it. A few days
afterwards the stolen pupæ or nymphæ emerge, without
memory of their childhood, and immediately and without
compulsion take part in all tasks.
According to Büchner's account,[30]--
From time to time the army makes a short halt, partly
to let the rearguard close up, partly because
different opinions arise as to the direction of the
host, or because the place at which they are is
unknown to them. Forel several times saw the army
completely lose its way--an incident only once
observed by Huber. Forel puts the number of warriors
in such an army at from one hundred to more than two
thousand. Its speed is on an average a mètre per
minute, but varies much according to circumstances,
and is naturally least when returning laden with
booty. If the distance be very great, such bodily
fatigue may at last be felt that the whole attack on
the hostile nest is given up, and a retreat is begun;
Forel once saw this happen after they had passed over
a distance of two hundred and forty yards. Sometimes
it seems as though, on coming within sight of the
hostile nest, a kind of discouragement took possession
of them, and prevented their making the attack. If the
nest cannot at once be found, the whole army halts,
and some divisions are sent forward to search for it,
and these are gradually seen returning towards the
centre. Forel also saw such an army only searching the
first day, advancing zigzag, and with frequent halts,
whereas on the following day it went forward to its
aim swiftly and without delay, having found out the
road. It seems that a single ant, even if it knows the
way and the place, is not able alone to lead a large
army, but that a considerable number must be employed
in this duty. Mistakes as to the road occur with
special ease during the return journey, because the
several ants are laden with booty and cannot readily
understand each other. Individual ants are then seen
to wander about in every direction often for a long
time, until they at last reach a spot known to them,
and then advance swiftly to their goal. Many never
come back at all. These mistakes easily occur when the
robbers which have passed into a hostile nest do not
come out again at the same holes whereby they entered,
but by others at some distance--for instance, by a
subterranean canal. Coming out thus in a strange
neighbourhood, they do not know which way to take, and
only some chance to find the right road during their
aimless wanderings about, and recognise and follow it
by smell. On the other hand, such mistakes scarcely
ever happen to individuals in an unladen train, kept
in good array. Other species of ants (_F. fusca_,
_rufa_, _sanguinea_) know better how to manage under
such circumstances than do the Amazons. The laden ones
lay down their loads, first find where they are, and
only take them up again after they have found their
way. If the booty seized in the nest first attacked is
too large to be all taken at once, the robbers return
once, or oftener, so as to complete their work. . . .
The ants, as already said, have no regular leaders nor
chiefs, yet it is certain that in each expedition,
alteration of road, or other change, the decision
during that event comes from a small knot of
individuals, which have previously come to an
understanding, and carry the rest and the undecided
along with them. These do not always follow
immediately, but only after they have received several
taps on the head from the members of the 'ring.' The
procession does not advance until the leaders have
convinced themselves by their own eyesight that the
main part of the army is following.
One day Forel saw some Amazons on the surface of a
nest of the _F. fusca_ seeking and sounding in all
directions, without being able to find the entrance.
At last one of them found a very little hole, hardly
as large as a pin's head, through which the robbers
penetrated. But since, owing to the smallness of the
hole, the invasion went on slowly, the search was
continued, and an entrance was found further off,
through which the Amazon army gradually disappeared.
All was quiet. About five minutes later Forel saw a
booty-laden column emerge from each hole. Not a single
ant was without a load. The two columns united outside
and retreated together.
A marauding excursion of the Amazons against the _F.
rufibarbis_, a sub-species of the _F. fusca_, or small
black ants, took place as follows:--The vanguard of
the robber army found that it had reached the
neighbourhood of the hostile nest more quickly than it
had expected; for it halted suddenly and decidedly,
and sent a number of messengers which brought up the
main body and the rearguard with incredible speed. In
less than thirty seconds the whole army had closed up,
and hurled itself in a mass on the dome of the hostile
nest. This was the more necessary as the _rufibarbes_
during the short halt had discovered the approach of
the enemy, and had utilised the time to cover the dome
with defenders. An indescribable struggle followed,
but the superior numbers of the Amazons overcame, and
they penetrated into the nest, while the defenders
poured by thousands out of the same holes, with their
larvæ and pupæ in their jaws, and escaped to the
nearest plants and bushes, running over the heaps of
their assailants. These looked on the matter as
hopeless, and began to retreat. But the _rufibarbes_,
furious at their proceedings, pursued them, and
endeavoured to get away from them the few pupæ they
had obtained, by trying to seize the Amazons' legs and
to snatch away the pupæ. The Amazon lets its jaws slip
slowly along the captive pupa, as far as the head of
its opponent, and pierces it, if it does not, as
generally happens, draw back. But it often manages to
seize the pupa at the instant at which the Amazon lets
it go and flies with it. This is managed yet more
easily when a comrade holds the robber by the legs,
and compels it to loose its prey in order to guard
itself against its assailant. Sometimes the robbers
seize empty cocoons and carry them away, but they
leave them on the road when they have discovered their
mistake. In the above case the strength of the
_rufibarbes_ proved at last so great that the
rearguard of the retreating army was seriously
pressed, and was obliged to give up its booty. A
number of the Amazons also were overpowered and
killed, but not without the _rufibarbes_ also losing
many people. None the less did some individuals, as
though desperate, rush into the thickest hosts of the
enemy, penetrated again into the nest, and carried off
several pupæ by sheer audacity and skill. Most of them
left their prey to go to the help of their comrades
when assailed by the _rufibarbes_. Ten minutes after
the commencement of the retreat all the Amazons had
left the nest, and, being swifter than their
opponents, they were only pursued for about halfway
back. Their attack had failed on account of a short
delay!
On another occasion observed by Forel, in which
several fertile Amazons also took part and killed many
enemies, the nest was thoroughly ravished, but the
retreat was also in this case very much disturbed and
harassed by the superior numbers of the enemy. There
were many slain on both sides. That in spite of the
above-mentioned unanimity different opinions among the
members of an expedition sometimes hinder its conduct,
the following observation seems to show:--An advancing
column divided after it had gone about ten yards from
the nest. Half turned back, while the other half went
on, but after some time hesitated and also turned
back. Arrived at home, it found those which had
formerly turned back putting themselves in motion in a
new direction. The newly returned followed them, and
the reunited army, after various wheelings, halts,
&c., at last turned home again by a long way round.
The whole business looked like a promenade. But
apparently different parties had different nests in
view, while others were entirely against the
expedition. Yet perhaps it was only a march for
exercise.
Outer obstacles do not, as a rule, hinder the Amazons
when they are once on the march. Forel saw them wade
through some shallow water, although many were drowned
in it, and then march over a dusty high road, although
the wind blew half of them away. As they returned,
booty-laden, neither wind, nor dust, nor water could
make them lay down their prey. They only got back with
great trouble, and turned back again to bring fresh
booty, although many lost their lives.
The following is also quoted from Büchner's excellent epitome of Forel's
observations in this connection:--
The most terrible enemy of the Amazons is the sanguine
ant (_F. sanguinea_), which also keeps slaves, and
thereby often comes into collision with the Amazons on
their marauding excursions. It is not equal to it in
bodily strength or fighting capacity, but surpasses it
in intelligence; according to Forel it is the most
intelligent of all the species of ants. If Forel, for
instance, poured out the contents of a sack filled
with a nest of the slave species near an Amazon nest,
the Amazons apparently generally regarded the tumbled
together heap of ants, larvæ, pupæ, earth, building
materials, &c., as the dome of a hostile nest, and
took all imaginable but useless pains to find out the
entrances thereinto, leaving on one side for this
investigation their only object, the carrying off the
pupæ; but the sanguine ants under similar
circumstances did not allow themselves to be deceived,
but at once ransacked the whole heap.
On another occasion, while a procession of Amazon ants was on its way to
plunder a nest of _F. fusca_, before it arrived Forel poured out a
sack-full of sanguine ants, and made a break in the nest:--
The sanguine ants pressed in, while the _fusca_ came
out to defend themselves. At this moment the first
Amazons arrived. When they saw the sanguine ants they
drew back and awaited the main army, which appeared
much disturbed at the news. But once united, the bold
robbers rushed at their foes. The latter gathered
together and beat back the first attack, but the
Amazons closed up their ranks and made a second
assault, which carried them on to the dome and into
the midst of the enemy. These were overthrown, as well
as a number of _F. pratensis_, which Forel at this
moment poured out on the nest. The conquerors delayed
for a moment on the dome after their victory, and then
entered the nest to bring out a little of the valuable
booty. A few Amazons which were mad with anger did not
return with the main army, but went on slaughtering
blindly among the conquered and the fugitives of the
three species, _fusca_, _pratensis_, and _sanguinea_.
The ravished _rufibarbes_ once became so desperate at
their overthrow that they followed the robbers to
their own nest, and the latter had some trouble in
defending it. The _rufibarbes_ let themselves be
killed in hundreds, and really seemed as though they
courted death. A small number of the Amazons also sank
under the bites of their enemies. The nest contained
slaves of the _rufibarbis_ species, which on this
emergency fought actively against their own race.
There were also slaves of the species _fusca_, so that
the nest included three different species of ants.
The same nest is often revisited many times on the
same day or at different periods, until either there
is no more to steal, or the plundered folk have hit
upon better mode of defence. A column which was in the
act of going back to such a plundered nest turned when
halfway there, and halted, apparently on no other
ground than because it had met the rearguard of the
army, and had learned that the nest was exhausted, and
that there was nothing more to be had there. The
robbers then went off to a _rufibarbis_ nest which was
in the neighbourhood, and killed half the inhabitants
while plundering the nest. The surviving _rufibarbes_
returned after the robbery and brought up new progeny;
but thirteen days later the Amazons again reaped a
rich harvest from the same nest. The Amazon army often
severs itself into two separate divisions when there
is not enough for both to do at the same spot.
Sometimes one division finds something and the other
nothing, and they then reunite. If any obstacle be
placed in their way they try to overcome it, in doing
which some leave the main army, lose themselves, and
only find their way home again with difficulty. Forel
has tried to establish the normal frequency of
expeditions, and found that a colony watched by
himself for a space of thirty days sent out no less
than forty-four marauding excursions. Of these about
eight-and-twenty were completely, nine partially, and
the remainder not at all successful. He four times saw
the army divide into two. Half the expeditions were
levelled against the _rufibarbes_, half against the
_fuscæ_. On an average a successful expedition would
bring back to the colony a thousand pupæ or larvæ. On
the whole, the number of future slaves stolen by a
strong colony during a favourable summer may be
reckoned at forty thousand!
The internecine battles which occasionally break out
among the Amazons themselves are naturally the most
cruel. They tear each other to pieces with incredible
fury, and knots of five or six individuals which have
pierced each other may be seen rolling over each other
on the ground, it being impossible to distinguish
between friend and foe. Civil wars among men are also
known to be the most embittered and the most bloody.
The mode of attack practised by the other best known species of
slave-making ant, _sanguinea_, is somewhat different:--
They march in small troops which, in case of need,
summon reinforcements, and therefore as a rule only
reach their goal slowly. Between the individual troops
messengers or scouts run continually backwards and
forwards. The first troop which arrives at the hostile
nest does not rush at it, as do the Amazons, but
contents itself with making provisional
reconnaissances, wherein some of the assailants are
generally made prisoners by the enemy, which have time
to bethink and to collect themselves. Reinforcements
are now brought up, and a regular siege of the nest
begins. A sudden invasion, like that of the Amazons,
is never seen. The besieging army forms a complete
ring round the hostile nest, and the besiegers hold
this with mandibles open and antennæ drawn back,
without going nearer. In this position they beat off
all assaults of the besieged, until they feel
themselves strong enough to advance to the attack.
This attack scarcely ever fails, and has for its chief
object the mastering of the entrances and outlets of
the nest. A special troop guards each opening, and
only allows such of the besieged to pass out as carry
no pupæ. This manoeuvre gives rise to a number of
comical and characteristic scenes. By this means the
sanguine ants in a few minutes manage to have all the
defenders out of the nests and the pupæ left behind.
This is the case at least with the _rufibarbes_, while
the rather less timid _fuscæ_ try, even at the last
moment when it is useless, to stop up or barricade the
entrances. The sanguine ants do not indeed possess the
terrible weapons and the warlike impetuosity of the
Amazons, but they are stronger and larger. If a
_fusca_ or a _rufibarbis_ fights with a sanguine ant
for the possession of a pupa, it is generally very
soon overcome. While the main part of the army is
penetrating into the nest to steal the pupæ, some
divisions pursue the fugitives, to take away from them
the few pupæ which may chance to have been saved. They
drive them even out of the cricket-holes in which they
have meanwhile taken refuge. In short, it is a
_razzia_, or sweeping burglary, as complete as can be
imagined. In the retreat the robbers in no wise hurry
themselves, for they know that they are threatened by
no danger and no loss, and the complete emptying of a
large and distant nest often takes several days in
accomplishing. The ants which have been so thoroughly
robbed scarcely ever return to their former abode.
It must be admitted that a human army, robbing a
foreign town or fortress, could not behave better or
more prudently.
Huber gives the following account of a battle waged by sanguine ants:--
At ten, in a July morning, he noticed a small band of
them emerge from their nest, and march rapidly towards
a nest of negroes, around which it dispersed. A number
of the blacks rushed out, gave battle, and succeeded
in defeating their invaders, and in making several of
them prisoners. Upon this, the remainder of the
attacking force waited for a reinforcement. When this
came up, they still declined further proceedings, and
sent more aides-de-camp to their own nest. The result
of these messages was a much larger reinforcement; but
even yet the pirates appeared to shun the combat. At
last, the negroes marched out from their nest in a
phalanx of about two feet square, and a number of
skirmishes began, which soon ended in a general
_mêlée_. Long before the event seemed certain, the
negroes carried off their pupæ to the most distant
part of the nest; and when, after a longer encounter,
they appeared to think further resistance vain, they
retreated, attempting to take with them their young.
In this, however, they were prevented, and the
invaders obtained possession of their nest and the
booty. When they had done this, they put in a
garrison, and occupied the night and the succeeding
day in carrying off their spoil.
Büchner says--
Battles between ants of the same species often end
with a lasting alliance, especially when the number of
the workers on both sides is comparatively small. The
wise little animals under such circumstances discover,
much more quickly and better than men, that they can
only destroy each other by fighting, while union would
benefit both parties. Sometimes they drive each other
out of their nests in a quite friendly way. Forel laid
on a table a piece of bark with a nest of the gentle
_Leptothorax acervorum_, and then put on it the
contents of another nest of the same species. The last
comers were by far the more numerous, and soon
possessed themselves of the nest, driving out the
inmates. But the latter did not know whither to go,
and turned back again. They were then seized by their
opponents one after the other, carried away as far as
possible from the nest, and there put down. The
oftener they came back the further were they carried
away. One of the carriers arrived in this fashion at
the edge of the table, and after it had by means of
its feelers convinced itself that it had reached the
end of the world, mercilessly let its burden drop into
the fathomless abyss. It waited a moment to see if it
had attained its object, and then turned back to the
nest. Forel picked up the ant which had fallen on the
floor, and put it down right in front of the returning
ant. The latter repeated the same manoeuvre as at
first, only stretching its neck further over the edge
of the table. He several times reiterated his
experiment, and always with the same result. Later the
two colonies were shut up together in a glass case,
and gradually learned to agree.
At other times, however, warlike ants show great and needless cruelty to
one another:--
They slowly pull from their victim, that is rendered
defenceless by wounds, exhaustion, or terror, first
one feeler and then the other, then the legs one after
another, until they at last kill it, or pull it in a
completely mutilated and helpless condition to some
out-of-the-way spot where it perishes miserably. Yet
some compassionate hearts are to be found among the
victors, which only pull the conquered to a distant
place in order to get rid of them, and there let them
go without injuring them.
The following account is also taken from Büchner's 'Mind in Animals,' p.
87:--
The doors are often guarded by special sentries, which
fulfil their important duty in various ways. Forel saw
a nest of the _Colobopsis truncata_, the two or three
very small round openings of which were watched by
soldiers, arranged so that their thick cylindrical
heads stopped them up, just as a cork stops up the
mouth of a bottle. The same observer saw the
_Myrmecina Latreillei_ defend themselves against the
invasions of the slave-making _Strongylognathus_, by
placing a worker at each of the little openings of the
nest, which quite stops up the opening either with
its head or abdomen. The _Camponotus_ species also
defend their nests by stretching their heads in front
of the openings, drawing back the antennæ. Each
approaching enemy thus receives a sharp blow or bite
delivered with the whole weight of the body. MacCook
noticed in the nests of the soon to be described
Pennsylvanian mound-building ants, the employment of
special sentries, which lay watching within the nest
entrances, and sprang out at the first sight of danger
to attack the enemy; and it was wonderful to see with
what swiftness the news of such an alarm spread
through the nest, and how the inhabitants came out _en
masse_ to meet the enemy. The _Lasius_ species defend
their large, strong, and very extensive nests against
hostile attack or sieges with equal courage and skill,
while other timid species seek to fly as speedily as
possible with their larvæ, pupæ, and fruitful queens.
There is, as Forel tells us, a regular barricade
fight. Passage after passage is stopped and defended
to the uttermost, so that the assailants can only
advance step and step. Unless the latter are in an
enormous majority, the struggle may last a very long
time with these tactics. During this time, other
workers are busy preparing subterranean passages
backwards for eventual flight. Generally such passages
are already made, and during a fight a new dome of the
_Lasius_ may be seen rising at a distance, it not
being difficult for them to make this with the help of
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