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.