Chapter III: Ants (5)

Lastly, there are two species of Eciton totally blind, and their habits differ from those of the species which we have hitherto considered. Bates writes of them:--

The armies of _E. vastator_ and _E. erratica_ move, as
far as I could learn, wholly under covered roads, the
ants constructing them gradually but rapidly as they
advance. The column of foragers pushes forward step by
step, under the protection of these covered passages,
through the thickets, and on reaching a rotting log,
or other promising hunting-ground, pour into the
crevices in search of booty. I have traced their
arcades, occasionally, for a distance of one or two
hundred yards; the grains of earth are taken from the
soil over which the column is passing, and are fitted
together without cement. It is this last-mentioned
feature that distinguishes them from the similar
covered roads made by termites, who use their
glutinous saliva to cement the grains together. The
blind Ecitons, working in numbers, build up
simultaneously the sides of their convex arcades, and
contrive, in a surprising manner, to approximate them
and fit in the key-stones without letting the loose
uncemented structure fall to pieces. There was a very
clear division of labour between the two classes of
neuters in these blind species. The large-headed
class, although not possessing monstrously lengthened
jaws like the worker-majors in _E. hamata_ and _E.
drepanophora_, are rigidly defined in structure from
the small-headed class, and act as soldiers, defending
the working community (like soldier termites) against
all comers. Whenever I made a breach in one of their
covered ways, all the ants underneath were set in
commotion, but the worker-minors remained behind to
repair the damage, whilst the large-heads issued forth
in a most menacing manner, rearing their heads and
snapping their jaws with an expression of the fiercest
rage and defiance.

_Annornia arcens._--This is the so-called 'driver' or 'marching' ant of West Africa, which in habits and intelligence closely resembles the military ants of the other hemisphere. I shall therefore not wait again to describe these habits in detail. Like the Ecitons, the marching ants of Africa have no fixed nest, but make temporary halts in the shade of hollow trees, overhanging rocks, &c. They march in large armies, and, like the Ecitons, always in the form of a long close column; but in this case the relative position of the carriers of spoil and larvæ is reversed, for while these occupy the middle place the soldiers and officers march on either side. These have large heads armed with powerful jaws, and never take part in carrying; their function is to maintain order, act as scouts, and attack prey. The habits of these ants resemble most closely those of the blind Ecitons in that they very frequently, and indeed generally, build covered ways; they do so apparently in order to protect themselves from the heat of the African sun. Their line of march is therefore marked by a continuous arch or tunnel, which is always being constructed by the van of the column. The structure is made of earth moulded together by saliva, and is very quickly built. But it is only built in places where the line of march is exposed to the sunlight; at night, or in the shadow of trees or long grass, it is not made. If their camp is flooded by a tropical rainstorm, the ants congregate in a close mass, with the younger ants in the centre; they thus form a floating island.

It is remarkable that ants of different hemispheres should manifest so close a similarity with respect to all these wonderful habits. The Chasseur ants of Trinidad, and, according to Madame Merian, the ants of visitation of Cayenne, also display habits of the same kind.

_General Intelligence of Various Species._

Many of the foregoing facts display an astonishing degree of intelligence as obtaining among ants; for I think that however much latitude we may be inclined to allow to 'blind instinct' in the way of imitating actions elsewhere due to conscious purpose, some at least of these foregoing facts can only be fairly reconciled with the view that the insects know what they are doing and why they are doing it. But as I am myself well aware of the difficulty that arises in all such cases of drawing the line between purposeless instinct and purposive intelligence, I have thought it desirable to reserve for this concluding division of the present chapter several isolated facts which have been observed among sundry species of ants, and which do not seem to admit of being reasonably comprised under the category of instinctive action, if by the latter we mean action pursued without knowledge of the relation between the means adopted and the ends attained.

It will be remembered that our test of instinctive as distinguished from truly intelligent action is simply whether all individuals of a species perform similar adaptive movements under the stimulus supplied by similar and habitual circumstances, or whether they manifest individual and peculiar adaptive movements to meet the exigencies of novel and peculiar circumstances. The importance of this distinction may be rendered manifest by the following illustrations.

We have already seen that the ants which Sir John Lubbock observed display many and complex instincts, which together might seem to justify us in anticipating that animals which present such wonderful instincts must also present sufficient general intelligence to meet simple though novel exigencies by such simple adaptations as the unfamiliar circumstances require. Yet experiments which he made in this connection seem to show that such is not the case, but that these ants, with all their wealth of instinctive endowments, are utterly destitute of intelligent resources; they have abundance of common and detailed knowledge (supposing the adaptations to be made consciously) how to act under certain complex though familiar circumstances, but appear quite unable to originate any adaptive action to obviate even the simplest conceivable difficulty, if this is of a kind which they have not been previously accustomed to meet. Thus, on a horizontal rod B supported in a saucer of water S, and therefore inaccessible to the ants from beneath, he placed some larvæ A. On the nest N he then placed a block of wood C D, constructed so that the portion D should touch the larvæ at A. When the ants had made a number of journeys over C D A and back again, he raised the block C D so that there was an interval 3/10 of an inch between the end of the block D and the larvæ at A.

The ants kept on coming, and tried hard to reach down
from D to A, which was only just out of their
reach. . . . After a while they all gave up their
efforts and went away, losing their prize in spite of
most earnest efforts, because it did not occur to them
to drop 3/10 of an inch. At the moment when the
separation was made there were fifteen ants on the
larvæ. These could, of course, have returned if one had
stood still and allowed the others to get on its back.
This, however, did not occur to them; nor did they
think of letting themselves drop from the bottom of the
paper (P) on to the nest. Two or three, indeed, fell
down, I have no doubt by accident; but the remainder
wandered about, until at length most of them got into
the water.

In another experiment he interposed a light straw bridge on the way between the nest and the larvæ, and when the ants had well learnt the way, he drew the bridge a short distance towards the nest, so that a small chasm was made in the road. The ants tried hard and ineffectually to reach across it, but it did not occur to them to _push_ the straw into its original position.

The following experiment is still more illustrative of the absence of intelligence, because the adjustive action required would not demand the exercise of such high powers of imagination and abstraction as would have been required for the moving forwards of the paper drawbridge.

To test their intelligence I made the following
experiments: I suspended some honey over a nest of
_Lasius flavus_ at a height of about 1/2 an inch, and
accessible only by a paper bridge more than 10 feet
long. Under the glass I then placed a small heap of
earth. The ants soon swarmed over the earth on to the
glass, and began feeding on the honey. I then removed
a little of the earth, so that there was an interval
of about 1/3 of an inch between the glass and the
earth; but though the distance was so small, they
would not jump down, but preferred to go round by the
long bridge. They tried in vain to stretch up from the
earth to the glass, which, however, was just out of
their reach, though they could touch it with their
antennæ; but it did not occur to them to heap the
earth up a little, though if they had moved only half
a dozen particles of earth they would have secured for
themselves direct access to the food. This, however,
never occurred to them. At length they gave up all
attempts to reach up to the glass, and went round by
the paper bridge. I left the arrangement for several
weeks, but they continued to go round by the long
paper bridge.

Another and somewhat similar experiment consisted in placing an upright stick A, supporting at an angle another stick B, which nearly but not quite touched the ground at C. At the end of the stick B there were placed some larvæ in a horizontal glass cell at D. Into this cell were also placed a number of ants along with the larvæ. The drop from D to C was only 1/2 an inch; 'still, though the ants reached over and showed a great anxiety to take this short cut home, they none of them faced the leap, but all went round by the sticks, a distance of nearly 7 feet.' Sir John then reduced the interruption to 2/5 of an inch, so that the ants could even touch the glass cell with their antennæ; yet all day long the ants continued to go the long way round rather than face the drop. Next, therefore, he took still longer sticks and tapes, and arranged them as before, only horizontally instead of vertically. He also placed some fine earth under the glass cell containing the larvæ. The ants as before continued to go the long way round (16 feet), though the drop could not have hurt either themselves or the larvæ, and though even this drop might have been obviated by heaping up the fine earth into a little mound 1/8 of an inch high, so as to touch the glass cell.

It is desirable, however, here to state that all species of ants do not show this aversion to allowing themselves to drop through short distances; for Moggridge describes the harvesting ants of Europe as seeming rather to enjoy acrobatic performances of this kind; and the same fact is recorded by Belt of the leaf-cutting ants of the Amazons. Dr. Bastian, in his work on 'Brain as an Organ of Mind,' suggests that the 'seeming lack of intelligence betrayed by our English ants, from their disinclination to take a small leap, may be due simply to their defective sight' (pp. 241-2). But even this consideration does not extenuate the stupidity of the ants which failed to heap up the fine earth to reach the glass cell which they were able to touch with their antennæ.

That the species of ants on which Sir John Lubbock experimented were not, however, quite destitute of intelligence is proved by the result of the following experiment:--

I put some provisions in a shallow box with a glass
top and a single hole in one side; I then put some
specimens of _Lasius niger_ to the food, and soon a
stream of ants was at work busily carrying supplies
off to the nest. When they had got to know their way
thoroughly, and from thirty to forty were so occupied,
I poured some fine mould in front of the hole, so as
to cover it to a depth of about 1/2 an inch. I then
took out the ants which were actually in the box. As
soon as the ants had recovered from the shock of this
unexpected proceeding on my part, they began to run
all round and about the box, looking for some other
place of entrance. Finding none, however, they began
digging down into the earth just over the hole,
carrying off the grains of earth one by one and
depositing them without any order all round at a
distance of from 1/2 to 6 inches, until they had
excavated down to the doorway, when they again began
carrying off the food as before.

This experiment was several times repeated on _L. niger_ and on _L. flavus_, always with the same result.

Thus, then, we may conclude that the reasoning power of these ants, although shown by the first experiments to be almost _nil_, is shown by this experiment to be not quite _nil_; for the attempt to meet the exigencies of the case by first going round the box to seek another entrance, before taking the labour to remove the earth from the known entrance, implies a certain rudimentary degree of adaptive capacity which belongs to the category of the rational.

Another point of considerable interest, as bearing on the general intelligence of ants, is one that was brought out as the result of a laborious series of hourly observations, extending without intermission from 6.30 A.M. to 10 P.M. for a period of three months. The object of these observations was to ascertain whether the principle of the division of labour is practised by the ants. The result of these observations was to show that during the winter-time, when the ants are not active, certain individuals are told off to forage for supplies, and that when any casualty overtakes these individuals, others are told off to supply their places. Thus, in the words of Sir John Lubbock's analysis of his lengthy tables,--

The feeders at the beginning of the experiment were
those known to us as Nos. 5, 6, and 7. On the 22nd of
November a friend, registered as No. 8, came to the
honey, and again on the 11th December; but with these
two exceptions the whole of the supplies were carried
in by Nos. 5 and 6, with a little help from No. 7.
Thinking now it might be alleged that possibly these
were merely unusually active or greedy individuals, I
imprisoned No. 6 when she came out to feed on the 5th.
As will be seen from the table, no other ant had been
out to the honey for some days; and it could therefore
hardly be accidental that on that very evening another
ant (then registered as No. 9) came out for food. This
ant, as will be seen from the table, then took the
place of No. 6 (No. 5 being imprisoned). On the 11th
January No. 9 took in all the supplies, again with a
little help from No. 7. So matters continued until the
17th, when I imprisoned No. 9, and then again, _i.e._
on the 19th, another ant (No. 10) came out for the
food, aided, on and after the 22nd, by another (No.
11). This seems to me very curious. From the 1st
November to the 5th January, with two or three casual
exceptions, the whole of the supplies were carried in
by three ants, one of whom, however, did comparatively
little. The other two are imprisoned, and then, but
not till then, a fresh ant appears on the scene. She
carries in the food for a week, and then she being
imprisoned, two others undertake the task. On the
other hand, in nest 1, when the first foragers were
not imprisoned, they continued during the whole time
to carry in the necessary supplies.

The facts, therefore, certainly seem to indicate that certain ants are told off as foragers, and that during winter, when but little food is required, two or three such foragers are sufficient to provide it.

Although Sir John Lubbock's ants showed such meagre resources of intelligent adjustment, other species of ants, which we have already had occasion to consider, appear to be as remarkable in this respect as they are in respect of their instinctive adjustments. Unfortunately observations on this subject are very sparse, but such as they are they hold out a strong inducement for any one who has the opportunity to experiment with the view of testing the intelligence of those species in connection with which the following observations have been made.

Réaumur states that ants will make no attempt to enter
an inhabited beehive to get at the contained honey,
knowing that the bees will slaughter them if they do
so. But if the hive is uninhabited, or the bees all
dead, the ants will swarm into the hive as long as any
honey is to be found there.

P. Huber records that a wall which had been partly erected by ants was observed by him--

As though it were intended to support the still
unfinished arched roof of a large room, which was
being built from the opposite side. But the workers
which had begun the arch had given it too low an
elevation for the wall on which it was to rest, and if
it had been continued on the same lines it would have
met the partition wall halfway up, and this was to be
avoided. I had just made this criticism to myself,
when a new arrival, after looking at the work, came to
the same conclusion. For it began at once to destroy
what had been done, and to heighten the wall on which
it was supported, and to make a new arch with the
materials of the old one under my very eyes. When the
ants begin an undertaking it seems exactly as if an
idea slowly ripened into execution in their minds.
Thus if one of them finds two stalks lying crosswise
on the nest, which make possible the formation of a
room, or some little rafters which suggest the walls
and the corners, it first observes the various parts
accurately, and then quickly and neatly heaps little
pellets of earth in the interspaces and alongside the
stalks. It brings from every side materials that seem
appropriate, and sometimes takes such from the
uncompleted works of its companions, so much is it
urged on by the idea which it has once conceived, and
by the desire to execute it. It goes and comes and
turns back again, until its plan is recognisable by
the others.

Ebrard, in his 'Etudes de Moeurs' (p. 3), gives the following remarkable instance of the display of intelligence of _F. fusca_:--

The earth was damp and the workers were in full
swing. It was a constant coming and going of ants,
coming forth from their underground dwelling, and
carrying back little pellets of earth for building. In
order to concentrate my attention I fixed my gaze on
the largest of the rooms which were being built,
wherein several ants were busy. The work had made
considerable progress; but although a projection could
be plainly seen along the upper edge of the wall,
there remained an interspace of about twelve or
fifteen millimetres to fill in. Here would have been
the place, in order to support the earth still to be
brought in, to have had recourse to those pillars,
buttresses, or fragments of dried leaves, which many
ants are wont to use in building. But the use of this
expedient is not customary with the ants I was
observing (_F. fusca_). Our ants, however, were
sufficient for the occasion. For a moment they seemed
inclined to leave their work, but soon turned instead
to a grass-plant growing near, the long narrow leaves
of which ran close together. They chose the nearest,
and weighted its distal end with damp earth, until its
apex just bent down to the space to be covered.
Unfortunately the bend was too close to the extremity,
and it threatened to break. To prevent this
misfortune, the ants gnawed at the base of the leaf
until it bent along its whole length and covered the
space required. But as this did not seem to be quite
enough, they heaped damp earth between the base of the
plant and that of the leaf, until the latter was
sufficiently bent. After they had thus attained their
object, they heaped on the buttressing leaf the
materials required for building the arched roof.

The characteristic _trait_ of the building of ants,
says Forel, is the almost complete absence of an
unchangeable model, peculiar to each species, such as
is found in wasps, bees, and others. The ants know how
to suit their indeed little perfect work to
circumstances, and to take advantage of each
situation. Besides, each works for itself and on a
given plan, and is only occasionally aided by others
when these understand its plan. Naturally many
collisions occur, and some destroy that which others
have made. This also gives the key to understanding
the labyrinth of the dwelling. For the rest, it is
always those workers which have discovered the most
advantageous method, or which have shown the most
patience, which win over to their plan the majority of
their comrades and at last the whole colony, although
not without many fights for supremacy. But if one
succeeds in obtaining a second to follow it, and this
second draws the others after it, the first is soon
lost again in the crowd.

Espinas also observed ('Thierischen Gesellschaften,' German translation, 1879, p. 371) that each single ant made its own plan and followed it until a comrade, which had caught the idea, joined it, and then they worked together in the execution of the same plan.

Moggridge says of the harvesters of Europe,--

I have observed on more than one occasion that when in
digging into an ants' nest I have thrown out an
_elater_ larva, the ants would cluster round it and
direct it towards some small opening in the soil,
which it would quickly enlarge and disappear down. At
other times, however, the ants would take no notice of
the _elater_, and it is my belief that the attentions
paid to it on former occasions were purely selfish,
and that they intended to avail themselves of the
tunnel thus made down into the soil, with the view of
reopening communications with the galleries and
granaries concealed below, the approaches to which had
been covered up. I have frequently watched the ants
make use of these passages mined by the _elater_ on
these occasions.

And again, as showing apparently intelligent adaptation of their usual habits to altered circumstances, he gives an account of the behaviour of these ants when a great crowd of them were confined by him in a glass jar containing earth. He says:--

On the following morning the openings were ten in
number, and the greatly increased heaps of excavated
earth showed that they must probably have been at work
all night. The amount of work done in this short time
was truly surprising, for it must be remembered that,
eighteen hours before, the earth presented a perfectly
level surface, and the larvæ and ants, now housed
below, found themselves prisoners in a strange place,
bounded by glass walls, and with no exit possible.

It seems to me that the ants displayed extraordinary
intelligence in having thus at a moment's notice
devised a plan by which the superabundant number of
workers could be employed at one time without coming
in one another's way. The soil contained in the jar
was of course less than a tenth part of that comprised
within the limits of an ordinary nest, while the
number of workers was probably more than a third of
the total number belonging to the colony. If therefore
but one or two entrances had been pierced in the soil,
the workers would have been for ever running against
one another, and a great number could never have got
below to help in the all-important task of preparing
passages and chambers for the accommodation of the
larvæ. These numerous and funnel-shaped entrances
admitted of the simultaneous descent and ascent of
large numbers of ants, and the work progressed with
proportionate rapidity. After a few days only three
entrances, and eventually only one, remained open.

Concerning the harvesting ant of Texas, the following quotation may be made, under the present head, from MacCook. After remarking that these ants always select sunny places wherein to build their nests, or disks, he goes on to say that within a few paces of his tent--

A nest was made which was partly shaded by a small
mesquite tree that stood just beyond the margin of the
clearing. The sapling had probably grown up after the
location of the community, and for some reason had
been permitted to remain until too old to kill off.
The shadow thrown upon the pavement was very slight;
nevertheless, fifteen feet distant a new formicary was
being established. The path from the ranch to the
spring ran between this new hill and the old one, and
ants were in communication between the two. An opening
had been made in the ground, and the beginnings of a
new formicary were quite apparent. This is the only
instance observed of what seemed an attempt at
colonising or removing, and I associated it with the
presence of the small but growing shadow of the young
tree.

He also gives us a still more remarkable observation, which indeed, I must candidly say, does not appear to me credible. I am, therefore, glad to add that it does not appear very distinctly from the account whether the author himself made the observation, or had it narrated to him by his guide. But here is the observation in his own words:--

While studying the habits of the cutting ant I was
tempted to make a night visit to a farm some distance
from camp, by the farmer's story of depredations made
by these insects upon certain plants and vegetables. A
long, dark tramp, a blind and vain search among the
fields, compelled us at last to call out the
countryman from his bed. He led us directly to one of
the cutting ants' nests, which was overshadowed by a
young peach tree. 'There they be, sir,' cried he
triumphantly. They were agriculturals! So also were
the other nests shown. The reason for this confounding
of the two ants on the part of the people hereabouts,
and the reason for the 'cutting' operations of our
harvesters, will be explained farther on. It is only
in point here to say that the farmer affirmed that the
ants under the peach tree had stripped off the first
tender leaves last spring, so that scarcely one had
been left upon the limbs. I am convinced that the
reason for this onslaught was the desire to be rid of
the obnoxious shade, and open the formicary to the
full light of the sun.

From this account it is not very clear whether the writer himself saw evidence of the former denudation of the tree, and if so whether there was any indication, other than the word of the farmer, that the denudation had been effected by the ants. To make this conclusion credible the best conceivable evidence would be required, and this, unfortunately, is just what we find wanting. Somewhat the same remarks may be made on the following quotation from the same writer, though in this case his view is to some extent supported by an observation of Moggridge, as well as by that of Ebrard already quoted:--

Here I observed what appeared to be a new mode of
operation. The workers, in several cases, left the
point at which they had begun a cutting, ascended the
blade, and passed as far out toward the point as
possible. The blade was thus borne downward, and as
the ant swayed up and down it really seemed that she
was taking advantage of the leverage thus gained, and
was bringing the augmented force to bear upon the
fracture. In two or three cases there appeared to be a
division of labour; that is to say, while the cutter
at the roots kept on with her work, another ant
climbed the grass blade and applied the power at the
opposite end of the lever. This position may have been
quite accidental, but it certainly had the appearance
of a voluntary co-operation. I was sorry not to be
able to establish this last inference by a series of
observations, as the facts were only observed in this
one nest.

The observation of Moggridge, to which I have alluded as in some measure rendering support to the foregoing, is as follows. Speaking of European harvesters which he kept in an artificial nest for the purposes of close observation, he says:--

I was also in this way able to see for myself much
that I otherwise could not have seen. Thus I was able
to watch the operation of removing roots which had
pierced through their galleries, belonging to seedling
plants growing on the surface, and which was performed
by two ants, one pulling at the free end of the root,
and the other gnawing at its fibres where the strain
was greatest, until at length it gave way.

And again,--

Two ants sometimes combine their efforts, when one
stations itself near the base of the peduncle, and
gnaws it at the point of greatest tension, while the
other hauls upon and twists it. . . . I have occasionally
seen ants engaged in cutting the capsules of certain
plants, drop them, and allow their companions below to
carry them away.

Lastly, the statements of these three observers taken together serve to render credible the following quotation from Bingley,[43] who says that in Captain Cook's expedition in New South Wales ants were seen by Sir Joseph Banks and others--

As green as a leaf, which live upon trees and build
their nests of various sizes, between that of a man's
head and his fist. These nests are of a very curious
structure: they are formed by bending down several of
the leaves, each of which is as broad as a man's hand,
and gluing the points of them together so as to form a
purse. The viscous matter used for this purpose is an
animal juice. . . . Their method of bending down leaves
we had no opportunity to observe; but we saw thousands
uniting all their strength to hold them in this
position, while other busy multitudes were employed
within, in applying this gluten, that was to prevent
their returning back. To satisfy ourselves that the
leaves were bent and held down by the efforts of these
diminutive artificers, we disturbed them in their
work; and as soon as they were driven from their
station, the leaves on which they were employed sprang
up with a force much greater than we could have
thought them able to conquer by any combination of
their strength.

This remarkable fact also seems to be corroborated by the following independent observation of Sir E. Tennent:--

The most formidable of all is the great red ant, or
Dimiya. It is particularly abundant in gardens and on
fruit-trees; it constructs its dwellings by gluing the
leaves of such species as are suitable from their
shape and pliancy into hollow balls, and these it
lines with a kind of transparent paper, like that
manufactured by the wasp. I have watched them at the
interesting operation of forming these dwellings;--a
line of ants standing on the edge of one leaf bring
another into contact with it, and hold both together
with their mandibles till their companions within
attach them firmly by means of their adhesive paper,
the assistants outside moving along as the work
proceeds. If it be necessary to draw closer a leaf too
distant to be laid hold of by the immediate workers,
they form a chain by depending one from the other till
the object is reached, when it is at length brought
into contact, and made fast by cement.

I shall now pass on to the remarkable observation communicated to Kirby by Colonel Sykes, F.R.S., and which is thus narrated by Kirby in his 'History, Habits, and Instincts of Animals:'--

When resident at Poona, the dessert, consisting of
fruits, cakes, and various preserves, always remained
upon a small side table, in a verandah of the
dining-room. To guard against inroads, the legs of the
table were immersed in four basins filled with water;
it was removed an inch from the wall, and, to keep off
dust from open windows, was covered with a tablecloth.
At first the ants did not attempt to cross the water,
but as the strait was very narrow, from an inch to an
inch and a half, and the sweets very tempting, they
appear, at length, to have braved all risks, to have
committed themselves to the deep, to have scrambled
across the channel, and to have reached the objects of
their desires, for hundreds were found every morning
revelling in enjoyment: daily vengeance was executed
upon them without lessening their numbers; at last the
legs of the table were painted, just above the water,
with a circle of turpentine. This at first seemed to
prove an effectual barrier, and for some days the
sweets were unmolested, after which they were again
attacked by these resolute plunderers; but how they
got at them seemed totally unaccountable, till Colonel
Sykes, who often passed the table, was surprised to
see an ant drop from the wall, about a foot above the
table, upon the cloth that covered it; another and
another succeeded. So that though the turpentine and
the distance from the wall appeared effectual
barriers, still the resources of the animal, when
determined to carry its point, were not exhausted, and
by ascending the wall to a certain height, with a
slight effort against it, in falling it managed to
land in safety upon the table.

Colonel Sykes was a good observer, so that this statement, standing upon his authority, ought not, perhaps, to be questioned. But in all cases of remarkable intelligence displayed by animals, we naturally and properly desire corroboration, however good the authority may be on which the statement of such cases may rest. I will, therefore, add the following instances of the ingenious and determined manner in which ants overcome obstacles, and which so far lend confirmation to the above account.

Professor Leuckart placed round the trunk of a tree, which was visited by ants as a pasture for aphides, a broad cloth soaked in tobacco-water. When the ants returning home down the trunk of the tree arrived at the soaked cloth, they turned round, went up the tree again to some of the overhanging branches, and allowed themselves to drop clear of the obnoxious barrier. On the other hand, the ants which desired to mount the tree first examined the nature of the barrier, then turned back and procured from a distance little pellets of earth, which they carried in their jaws and deposited one after another upon the tobacco-cloth till a road of earth was made across it, over which the ants passed to and fro with impunity.

This interesting, and indeed surprising observation of Leuckart's is, in turn, a corroboration of an almost identical one made more than a century ago by Cardinal Fleury, and communicated by him to Réaumur, who published it in his 'l'Histoire des Insectes' (1734). The Cardinal smeared the trunk of a tree with birdlime in order to prevent the ants from ascending it; but the insects overcame the obstacle by making a road of earth, small stones, &c., as in the case just mentioned. In another instance the Cardinal saw a number of ants make a bridge across a vessel of water surrounding the bottom of an orange-tree tub. They did so by conveying a number of little pieces of _wood_, the choice of which material instead of earth or stones, as in the previous case, seems to betoken no small knowledge of practical engineering.

Büchner, after quoting these cases, proceeds to say (_loc. cit._, p. 120),--

The ants behaved in yet more ingenious fashion under
the following very similar circumstances. Herr G.
Theuerkauf, the painter (Wasserthorstr. 49, Berlin),
writes to the author, November 18, 1875: 'A maple tree
standing on the ground of the manufacturer, Vollbaum,
of Elbing (now of Dantzic), swarmed with aphides and
ants. In order to check the mischief, the proprietor
smeared about a foot width of the ground round the
tree with tar. The first ants who wanted to cross
naturally stuck fast. But what did the next? They
turned back to the tree and carried down aphides,
which they stuck down on the tar one after another
until they had made a bridge over which they could
cross the tarring without danger. The above-named
merchant, Vollbaum, is the guarantor of this story,
which I received from his own mouth on the very spot
whereat it occurred.'

Büchner also gives the following case on the authority of Karl Vogt (_loc. cit._, p. 128). An apiary of a friend was invaded by ants:--

To make this impossible for the future, the four legs
of the beehive-stand were put into small, shallow
bowls filled with water, as is often done with food in
ant-infested places. The ants soon found a way out of
this, or rather a way into their beloved honey, and
that over an iron staple with which the stand was
attached to a neighbouring wall. The staple was
removed, but the ants did not allow themselves to be
defeated. They climbed into some linden trees standing
near, the branches of which hung over the stand, and
then dropped upon it from the branches, doing just the
same as their comrades do with respect to food
surrounded by water, when they drop upon it from the
ceiling of the room. In order to make this impossible,
the boughs were cut away. But once more the ants were
found in the stand, and closer investigation showed
that one of the bowls was dried up, and that a crowd
of ants had gathered in it. But they found themselves
puzzled how to go on with their robbery, for the leg
did not, by chance, rest on the bottom of the bowl,
but was about half an inch from it. The ants were seen
rapidly touching each other with their antennæ, or
carrying on a consultation, until at last a rather
larger ant came forward and put an end to the
difficulty. It rose to its full height on its hind
legs, and struggled until at last it seized a rather
projecting splinter of the wooden leg, and managed to
take hold of it. As soon as this was done other ants
ran on to it, strengthened the hold by clinging, and
so made a little living bridge, over which the others
could easily pass.

The same author publishes the following very remarkable observation, quoted from a letter to him by Dr. Ellendorf:--

It is a hard matter to protect any eatables from these
creatures, let the custody be ever so close. The legs
of cupboards and tables in or on which eatables are
kept are placed in vessels of water. I myself did
this, but I none the less found thousands of ants in
the cupboard next morning. It was a puzzle to me how
they crossed the water, but the puzzle was soon
solved; for I found a straw in one of the saucers,
which lay obliquely across the edge of the pan and
touched the leg of the press: this they had used for a
bridge. Hundreds were drowned in the water, apparently
because disorder had reigned at first, those coming
down with booty meeting those going up. But now there
was perfect order; the descending stream used one side
of the straw, the ascending the other. I now pushed
the straw about an inch away from the cupboard leg; a
terrible confusion arose. In a moment the leg
immediately over the water was covered with hundreds
of ants, feeling for the bridge in every direction
with their antennæ, running back again and coming in
ever larger swarms, as though they had communicated to
their comrades within the cupboard the fearful
misfortune that had taken place. Meanwhile the
new-comers continued to run along the straw, and not
finding the leg of the cupboard the greatest
perplexity arose. They hurried round the edge of the
pan, and soon found out where the fault lay. With
united forces they quickly pulled and pushed at the
straw, until it again came into contact with the wood,
and the communication was again restored.

This observation is strikingly, though unconsciously, confirmed by a recent writer in the _Leisure Hour_ (1880, pp. 718-19), who having been much troubled by small red ants in the tropics swarming over his provisions, placed the latter in a meat-safe detached from the wall and standing on four legs, each of which was placed in a little tin vessel containing water. Eight or ten days afterwards he found his provisions in the safe swarming with ants as before, and on investigating their mode of access to them found--

Proceeding along the whitewashed wall a string of ants
going and coming from the outer door to a height of
four feet on my wall, and corresponding with that of
the safe; and looking between it and the wall, I
discovered the secret--the bridge which these
persevering little insects had made. It consisted of a
broken bit of straw, which rested with one end on a
mud buttress fixed to the wall, and the other on the
overhanging or projecting top of the safe, which came
within an inch and a half of the wall. So they must
have carried the straw up from the floor, and resting
their end of it on the support they had prepared, let
it fall until its other end reached the safe, and then
crossed and completed the structure, for it was
fastened at both ends with the mortar composed of
their saliva and fine earth. Ruthlessly I destroyed
the bridge, and moving the safe farther from the wall,
managed to prevent their inroads for that season at
least. Since then I have frequently seen short
bridges, composed entirely of the concrete or mortar
which the white ants use to cover up their workings,
extending from a damp earthen wall to anything not
more than three-quarters of an inch from it.

Of the Ecitons Mr. Belt says:--

I shall relate two more instances of the use of a
reasoning faculty in these ants. I once saw a wide
column trying to pass along a crumbling, nearly
perpendicular slope. They would have got very slowly
over it, and many of them would have fallen, but a
number having secured their hold, and reaching to each
other, remained stationary, and over them the main
column passed. Another time they were crossing a
watercourse along a small branch, not thicker than a
goose-quill. They widened this natural bridge to three
times its width by a number of ants clinging to it and
to each other on each side, over which the column
passed three or four deep; whereas excepting for this
expedient they would have had to pass over in single
file, and treble the time would have been consumed.
Can it be contended that such insects are not able to
determine by reasoning powers which is the best way of
doing a thing?

Another observer, writing from the same part of the world to Büchner, gives a still more wonderful account of the ingenuity of Ecitons in crossing water. This observer is Herr H. Kreplin, of Heidemühl (Station Ducherom), 'who lived for nearly twenty years in South America as an engineer, and had often the opportunity of seeing the driver ants in the forests there.' He writes to Büchner, under date May 10, 1876, as follows:--

On both sides of the train, at about 10 mm. distance
from each other, stronger ants are to be seen,
distinguishable from the others by their foxy colour
and very thick heads with gigantic mandibles. These
'thickheads' play the same _rôle_ in the ant-state for
which they are cast in cultured communities. They look
after the order of the march, and allow none to turn
either to the right or left. The least confusion in
the regularity of the march makes them turn round and
put things straight again. While the procession of the
brown workers streams on unceasingly with a swarming
motion, the 'officers,' as the natives call these
thickheads, run constantly backwards and forwards,
ready to take the command on meeting any difficulty.
The crossing of streams by these creatures is the most
interesting point. If the watercourse be narrow, the
thickheads soon find trees, the branches of which meet
on the bank on either side, and after a short halt the
column set themselves in motion over these bridges,
rearranging themselves in the narrow train with
marvellous quickness on reaching the further side. But
if no natural bridge be available for the passage,
they travel along the bank of the river until they
arrive at a flat sandy shore. Each ant now seizes a
bit of dry wood, pulls it into the water, and mounts
thereupon. The hinder rows push the front ones even
further out, holding on to the wood with their feet
and to their comrades with their jaws. In a short time
the water is covered with ants, and when the raft has
grown too large to be held together by the small
creatures' strength, a part breaks itself off and
begins the journey across, while the ants left on the
bank busily pull their bits of wood into the water,
and work at enlarging the ferry-boat until it again
breaks. This is repeated as long as an ant remains on
shore. I had often heard described this method of
crossing rivers, but in the year 1859 I had the
opportunity of seeing it for myself.

It is remarkable that the military or driving ants of Africa exhibit precisely similar devices for the bridging of streams, namely, by forming a chain of individuals over which the others pass. By means of similar chains they also let themselves down from trees. It must be observed, however, that these and all the above observations, being independently made and separately recorded, serve to corroborate one another so strongly that we can entertain no reasonable doubt concerning the wonderful facts which they convey.

I shall now bring these numerous instances to a close with a quotation from Mr. Belt, which reveals in the most unequivocal manner surprising powers of observation and rational action on the part of the leaf-cutting ants of South America, whose general habits we have already considered:--

A nest was made near one of our tramways, and to get
to the trees the ants had to cross the rails, over
which the waggons were continually passing and
repassing. Every time they came along a number of ants
were crushed to death. They persevered in crossing for
some time, but at last set to work and tunnelled
underneath each rail. One day, when the waggons were
not running, I stopped up the tunnels with stones; but
although great numbers carrying leaves were thus cut
off from the nest, they would not cross the rails, but
set to work making fresh tunnels underneath them.

_Anatomy and Physiology of Nerve-centres and Sense-organs._

The foregoing facts concerning the intelligence of ants fully justifies Mr. Darwin's observation that 'the brain of an ant is one of the most marvellous atoms of matter in the world, perhaps more so than the brain of a man.' It may therefore be interesting in this particular case to depart from the lines otherwise laid down throughout the present work, and to devote a short section to the anatomy and physiology of this nerve-centre with its appended organs of sense.

The brain of an ant, then, is proportionally larger than that of any other insect. (See Titus Graber, 'Insects,' vol. i. p. 255.) In structure, also, the brain of an ant is in advance of that of other insects, its nearest analogue being the brain of a bee. The superiority of development is particularly remarkable with reference to the 'stalked bodies' of Dujardin; and these are largest in neuter workers, which are the most intelligent members of the community.

Injury of the brain causes, as in higher animals, tetanic spasms and involuntary reflex movements, followed by stupefaction.

An ant, whose brain has been perforated by the pointed
mandibles of an amazon, remains as though nailed to
its place; a shudder runs from time to time through
its body, and one of its legs is lifted at regular
intervals. It occasionally makes a short and quick
step, as though driven by an unseen spring, but, like
that of an automaton, aimless and objectless. If it is
pulled, it makes a movement of avoidance, but falls
back into its stupefied condition as soon as it is
released. It is no longer capable of action
consciously directed to a given object; it neither
tries to escape, nor to attack, nor to go back to its
home, nor to rejoin its companions, nor to walk away;
it feels neither heat nor cold, it knows neither fear
nor desire for food. It is merely an automatic and
reflex machine, and is exactly similar to one of those
pigeons from which Flourens removed the hemispheres of
the cerebrum. Just in the same way behaves the body of
an ant from which the head has been taken away. In the
numerous fights between amazons and other ants,
countless cases have been observed of slight injury to
the brain, which have caused the most remarkable
phenomena. Many of the wounded were seized with a mad
rage, and flung themselves at every one that came in
their way, whether friend or foe. Others assumed an
appearance of indifference, and walked serenely about
in the midst of the fighting. Others exhibited a
sudden failure of strength; but they still recognised
their enemies, approached them, and tried to bite them
in cold blood, in a way quite foreign to the behaviour
of healthy ants. They were also often observed to run
round and round in a circle, the motion resembling the
_manège_, or riding-school action of mammals, when one
of the crura cerebri has been removed.

If an ant is cut in half through the thorax, so that
the great nerve ganglia of the pro-thorax remain
untouched, the behaviour of the head shows that
intelligence also remains untouched. Ants mutilated in
this way try to go forwards with their two remaining
legs, and beg with their antennæ for their companions'
aid. If one of these latter lets itself be stopped,
then we observe a lively interchange of thanks and
sympathy expressed by the actively moving antennæ.
Forel placed near to each other two such mutilated
bodies of the _F. rufibarbis_. They conversed with
each other in the above-described way, and appeared
each to beg for help. But when he put in some
similarly mutilated ants of a hostile species, _F.
sanguinea_, the picture was changed; war broke out
between these cripples just in the same way and with
the same fury as between perfect ants.[44]

The antennæ appear to be the most important of the sense-organs, as their removal produces an extraordinary disturbance in the intelligence of the animal. An ant so mutilated can no longer find its way or recognise companions, and therefore is unable to distinguish between friends and foes. It is also unable to find food, ceases to engage in any labour, and loses all its regard for larvæ, remaining permanently quiet and almost motionless. A somewhat similar disturbance, or rather destruction, of the mental faculties is observable as a result of the same mutilation in the case of bees.[45]

FOOTNOTES:

[19] While this MS. is passing through the press Sir John Lubbock has read another paper before the Linnæan Society, which contains some important additional matter concerning the sense of direction in ants. It seems that in the experiment above described, the hat-box was not provided with a cover or lid, i.e. was not a 'closed chamber,' and that Sir John now finds the ants to take their bearings from the direction in which they observe the light to fall upon them. For in the experiment with the uncovered hat-box, if the source of light (candle) is moved round together with the rotating table which supports the box, the ants continue their way without making compensating changes in their direction of advance. The same thing happens if the hat-box is covered, so as to make of it a dark chamber. Direction of light being the source of their information that their ground is being moved, we can understand why they do not know that it is being moved when it is moved in the direction of their advance, as in the experiment with the paper slip.

[20] It is to be noted that although ants will attack stranger ants introduced from other nests, they will carefully tend stranger larvæ similarly introduced.