Chapter III: Ants (2)

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--