Chapter III: Ants (4)

It is not a little surprising to see that the ants
bring in not only seeds of large size and fallen
grain, but also green capsules, the torn stalks of
which show that they have been freshly gathered from
the plant. The manner in which they accomplish this
feat is as follows. An ant ascends the stem of a
fruiting plant of shepherd's-purse (_Capsella
bursa-pastoris_), let us say, and selects a
well-filled but green pod about midway up the stem,
those below being ready to shed their seeds at a
touch. Then, seizing it in its jaws, and fixing its
hind legs firmly as a pivot, it contrives to turn
round and round, and so strain the fibres of the
fruit-stalk that at length they snap. It then descends
to the stem, patiently backing and turning upwards
again as often as the clumsy and disproportionate
burden becomes wedged between the thickly set stalks,
and joins the line of its companions on their way to
the nest. In this manner capsules of chickweed
(_Stellaria media_) and entire calyces, containing the
nutlets of calamint, are gathered; two ants also
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 never seen a capsule
severed from its stalk by cutting alone, and the
mandibles of this ant are perhaps incompetent to
perform such a task. I have occasionally seen ants
engaged in cutting the capsules of certain plants,
drop them, and allow their companions below to carry
them away; and this corresponds with the curious
account given by Ælian of the manner in which the
spikelets of corn are severed and thrown down 'to the
people below,' [Greek: tô dêmô tô katô].

The recognition of the principle of the division of labour which the latter observation supplies, is further proved by the following quotation from the same author. A dead grasshopper which was being carried into their nest was--

Too large to pass through the door, so they tried to
dismember it. Failing in this, several ants drew the
wings and legs as far back as possible, while others
gnawed through the muscles where the strain was
greatest. They succeeded at last in thus pulling it
in.

The same thing is strikingly shown by the following quotation from Lespès:--

If the road from the place where they are gathering
their harvest to the nest is very long, they make
regular depôts for their provisions under large
leaves, stones, or other suitable places, and let
certain workers have the duty of carrying them from
depôt to depôt.

Büchner (_loc. cit._ p. 101) also makes the following references to the statements of previous observers:--

The subterranean workers of this remarkable genus are
very clever. The Rev. H. Clark reports from Rio de
Janeiro, that the _Sa-ubas_ have made a regular tunnel
under the bed of the river Parahyba, which is there as
broad as the Thames at London, in order to reach a
storehouse which is on the opposite bank. Bates tells
us that close to the Magoary rice-mills, near Para,
the ants bored through the dam of a large reservoir,
and the water escaped before the mischief could be
remedied. In the Para Botanical Gardens an
enterprising French gardener did everything he could
to drive the _Sa-ubas_ away. He lit fires at the chief
entrances of their nests, and blew sulphur vapour into
their galleries by means of bellows. But how
astonished was Bates when he saw the vapour come out
at no less a distance than seventy yards! Such an
extension have the subterranean passages of the
_Sa-ubas_.

The recognition of the principle of the division of labour, which is shown by the above observations, is further corroborated by the following quotation from Belt:--

Between the old burrows and the new one was a steep
slope. Instead of descending this with their burdens,
they cast them down on the top of the slope, whence
they rolled down to the bottom, where another relay of
labourers picked them up and carried them to the new
burrow. It was amusing to watch the ants hurrying out
with bundles of food, dropping them over the slope,
and rushing back immediately for more.

The same thing has been observed, as already stated, of the leaf-cutting ants--those engaged in cutting frequently throwing down the fragments of leaf which they cut to the carriers below. The prevalence of this habit among various species of ants therefore renders credible the following statements of Vincent Gredler of Botzen which are thus recorded in 'der Zool. Gart.,' xv. p. 434:--

In Herr Gredler's monastery one of the monks had been
accustomed for some months to put food regularly on
his window-sill for ants coming up from the garden.
In consequence of Herr Gredler's communications he
took it into his head to put the bait for the ants,
pounded sugar, into an old inkstand, and hung this up
by a string to the cross-piece of his window, and left
it hanging freely. A few ants were in with the bait.
These soon found their road out over the string with
their grains of sugar, and so their way back to their
friends. Before long a procession was arranged on the
new road from the window-sill along the string to the
spot where the sugar was, and so things went on for
two days, nothing fresh occurring. But one day the
procession stopped at the old feeding-place on the
window-sill, and took the food thence, without going
up to the pendent sugar-jar. Closer observation
revealed that about a dozen of the rogues were in the
jar above, and were busily and unwearyingly carrying
the grains of sugar to the edge of the pot, and
throwing them over to their comrades down below.

Many other instances of the division of labour might be given besides these, and those to be mentioned hereafter in other connections throughout the course of the present chapter; but enough has been said to show that the principle is unquestionably acted upon by sundry species of ants.

That ants are liable to make mistakes, and, when they do, that they profit by experience, is shown by the following experiment made by Moggridge; and many other instances might be given were it desirable:--

It sometimes happens that an ant has manifestly made a
bad selection, and is told on its return that what it
has brought home with much pains is no better than
rubbish, and is hustled out of the nest, and forced to
throw its burden away. In order to try whether these
creatures were not fallible like other mortals, I one
day took out with me a little packet of grey and white
porcelain beads, and scattered these in the path of a
harvesting train. They had scarcely lain a minute on
the earth before one of the largest workers seized
upon a bead, and with some difficulty clipped it with
its mandibles and trotted back at a great pace to the
nest. I waited for a little while, my attention being
divided between the other ants who were vainly
endeavouring to remove the beads, and the entrance
down which the worker had disappeared, and then left
the spot. On my return in an hour's time, I found the
ants passing unconcernedly by and over the beads which
lay where I had strewed them in apparently
undiminished quantities; and I conclude from this that
they had found out their mistake, and had wisely
returned to their accustomed occupations.

When the grain is thus taken into the nest, it is stored in regular granaries, but not until it has been denuded of its 'husks' or 'chaff.' The denuding process is carried on below ground, and the chaff is brought up to the surface, where it is laid in heaps to be blown away by the wind.

It is a remarkable thing, and one not yet understood, why the seed, when thus stored in subterranean chambers just far enough below the surface to favour germination, does not germinate. Moggridge says that out of twenty-one nests and among many thousands of seeds that he examined, he only found twenty-seven cases of incipient germination. Moreover, all these cases occurred in months from November to February, while in the nests opened in October, March, April, and May, no sprouted seeds were discovered, though these are the months highly favourable to germination. He is at a loss to suggest the treatment to which the ants expose the seeds in order to prevent their sprouting. 'Apparently it is not that moisture or warmth or the influence of atmospheric air is denied to the seeds, for we find them in damp soil in genial weather, and often at but a trifling distance below the surface of the ground;' and he has proved that the vitality of the seeds is not impaired, for he succeeded in raising crops of young plants from seeds removed from the granaries.

He also says,--

By a fortunate chance I have been able to prove that
the seeds will germinate in an undisturbed granary
when the ants are prevented from obtaining access to
it: and this goes to show not only that the structure
and nature of the granary chamber is not sufficient of
itself to prevent germination, but also that the
presence of the ants is essential to secure the
dormant condition of the seeds.

I discovered in two places portions of distinct nests
of _Atta structor_ which had been isolated owing to
the destruction of the hollow wall behind which they
lay, and then the granaries well filled up and
literally choked with growing seeds, though the earth
in which they lay completely enclosed and concealed
them until by chance I laid them bare. In one case I
knew that the destruction of the wall had only taken
place ten days before, so that the seeds had sprouted
in the interval.

My experiments also tend to confirm this, and to
favour the belief that the non-germination of the
seeds is due to some direct influence voluntarily
exercised by the ants, and not merely to the
conditions found in the nest, or to acid vapours which
in certain cases are given off by the ants themselves.

These experiments consisted in confining a large number of harvesting ants with their queen and larvæ in a glass test-tube partly filled with damp soil and various seeds, the whole being closed with a cork in the mouth of the test-tube. Under these circumstances the seeds all sprouted, showing that mere confinement in an atmosphere of exhalations from the ants did not prevent germination. Another series of experiments, undertaken at the suggestion of Mr. Darwin, on the effects of an atmosphere of formic acid, showed that although this vapour was very injurious to the seeds, it did not prevent their incipient germination. Therefore it yet remains to be ascertained why the seeds do not germinate in the granaries of the ants.

But in whatever way the ants manage to prevent germination, it is certain that they are aware of the importance in this connection of keeping the seeds as dry as possible; for Moggridge repeatedly observed that when the seeds which had been stored proved over-moist, the ants again took them out and spread them in the sun to dry, to be again brought into the nest after a sufficient exposure.

Lastly, he also repeatedly observed the most surprising and interesting fact that when, as we have seen was occasionally the case, the seeds did begin to germinate in the nests, the ants knew the most effective method of preventing the germination from proceeding; for he found that in these cases the ants gnawed off the tips of the radicles. This fact deserves to be considered as one of the most remarkable among the many remarkable facts of ant-psychology.

Passing on now to the harvesting or agricultural ants of Texas, attention was first called to the habits of this insect by Mr. Buckley in 1860,[40] and by Dr. Lincecum, who sent an account of his observations to Mr. Darwin, by whom they were communicated to the Linnæan Society in 1861. Five years later a paper was published in the Proceedings of the Academy of Natural Sciences of Philadelphia from the MS. of Dr. Lincecum. Lastly, in 1877 Mr. MacCook went to Texas expressly to study the habits of these insects, and he has recently embodied the results of his observations in a book of three hundred pages.[41] These observations are for the most part confirmatory of those of Lincecum, and for this as well as for reasons to be deduced from the work itself, they deserve to be accepted as trustworthy, notwithstanding that in some cases they are provokingly incomplete. The following is an epitome of these observations.

The ants clear away all the herbage above their nest in the form of a perfect circle, or 'disk,' 15 or 20 feet in diameter, by carefully felling every stalk of grass or weed that may be growing thereon. As the nests are placed in thickly grown localities, the effect of these bald or shaven disks is highly conspicuous and peculiar, exactly resembling in miniature the clearings which the settlers make in the American backwoods. The disk, however, is not merely cleared of herbage, but also carefully levelled, all inequalities of the surface being reduced by building pellets of soil into the hollows to an extent sufficient to make a uniformly flat surface. The action of rain and the constant motion of multitudes of ants cause this flat surface to become hard and smooth. In the centre of the disk is the gateway of the nest. This may be either a simple hole or a hollow cone.

From the disk in various directions there radiate ant-roads or avenues, which are cleared and smoothed like the disk itself, and which course through the thick surrounding grass, branching and narrowing as they go till they eventually taper away. These roads are usually three or four in number before they begin to branch, but may be as many as seven. They are usually two to three inches wide at their origin, but in large nests may be as much as five. MacCook found no road longer than sixty feet, but Lincecum describes one of three hundred feet. Along these hard and level roads there is always passing, during the daytime of the harvesting season, a constant stream of ants--those going from the nest being empty-handed, and those returning to it being laden with seeds. Of course the incoming ants, converging from all quarters upon the road, and therefore increasing in numbers as they approach the nest, require greater space for free locomotion; while the outgoing ants, diverging as they get further from home, also require greater proportional space the less their distance from the nest: hence the gradual swelling in the width of the roads as they approach the nests.

The manner of collecting the seeds in the jungle surrounding the roads is thus described by MacCook:--

At last a satisfactory seed is found. It is simply
lifted from the ground, or, as often happens, has to
be pulled out of the soil into which it has been
tightly pressed by the rain or by passing feet. Now
follows a movement which at first I thought to be a
testing of the seed, and which, indeed, may be
partially that; but finally I concluded that it was
the adjusting of the burden for safe and convenient
carriage. The ant pulls at the seed-husk with its
mandibles, turning and pinching or 'feeling' it on all
sides. If this does not satisfy, and commonly it does
not, the body is raised by stiffening out the legs,
the abdomen is curved underneath, and the apex applied
to the seed. I suppose this to be simply a mechanical
action for the better adjusting of the load. Now the
worker starts homeward. It has not lost itself in the
mazes of the grass forest. It turns directly towards
the road with an unerring judgment. There are many
obstacles to overcome. Pebbles, pellets of earth, bits
of wood, obtruding rootlets, or bent-down spears of
grass block up or hinder the way. These were scarcely
noticed when the ant was empty-handed. But they are
troublesome barriers now that she is burdened with a
seed quite as thick, twice as wide, and half as long
as herself. It is most interesting to see the skill,
strength, and rapidity with which the little harvester
swings her treasure over or around, or pushes it
beneath these obstacles. Now the seed has caught
against the herbage as the porter dodges under a too
narrow opening. She backs out and tries another
passage. Now the sharp points of the husk are
entangled in the grass. She jerks or pulls the burden
loose, and hurries on. The road is reached, and
progress is comparatively easy. Holding the grain in
her mandibles well above the surface, she breaks into
what I may describe with sufficient accuracy as 'a
trot,' and with little further interruption reaches
the disk and disappears within the gate. There are
variations from this behaviour, more or less marked,
according to the nature of the grounds, the seeds, and
(I suppose) the individuality of the harvesters; but
the mode of ingathering the crop is substantially as
above. Each ant operated independently. Once only did
I see anything like an effort to extend sympathy and
aid. A worker minor seeming to have difficulty in
testing or adjusting a large seed of buffalo-grass,
was assisted (apparently) by one worker major, and
then by another, after which she went on her way.

But these ants do not confine their harvesting operations to gathering fallen seeds; they will, like the ants of Europe, also cut seeds from the stalk.

In order to test the disposition of _crudelis_ to
garner the seeds from the stem, bunches of millet were
obtained from the North, and stalks eighteen inches
high, crowned by the boll of close-set seeds, were
stuck in the mound of an active formicary. The ants
mounted the stems and set to work vigorously to secure
the seeds, clusters of twenty or more being engaged at
once upon one head. The seeds were carried off and
stored within the nest. This experiment proved pretty
conclusively that in the seeding season _crudelis_
does not wait for the seeds to drop, but harvests them
from the plant.

The 'granaries' into which the seeds are brought are kept distinct from the 'nurseries' for the pupæ. Their walls, floor, and roof are so hard and smooth, that MacCook thinks the insects must practise upon them 'some rude mason's craft.'

He traced these granaries to a depth of four feet below the surface of the ground, and believes, from the statements of a native peasant, that they, or at least the formicaries, extend to a depth of fifteen feet.

As regards the care that the ants take of the gathered grain, Lincecum describes the same habit as Moggridge and Sykes describe--viz., the sunning of wet seeds to dry. MacCook, however, neglected to make any experiments on this subject. Neither has he been able to throw any light upon the question as to why the stored seeds do not germinate, and is doubtful whether the habit of gnawing the radicle of sprouting seeds, which prevails in the European species, is likewise practised by the American. On two other points of importance MacCook's observations are also incomplete. One of these has reference to an alleged statement, which he is disposed to believe, that when some ants in a community have been killed by poison, the survivors avoid the poison: he, however, made no experiments to test this statement.

The other main point on which his observations are defective has reference to a remarkable statement made by Lincecum in the most emphatic terms. This statement is that upon the surface of their disk the ants sow the seeds of a certain plant, called ant-rice, for the purpose of subsequently reaping a harvest of the grain. There is no doubt that the ant-disks do very often support this peculiar kind of grass, and that the ants are particularly fond of its seed; but whether the plant is actually sown in these situations by the insects, or grows there on account of these situations being more open than the general surface of the ground--this question MacCook has failed to answer, or even to further. We are, therefore, still left with Dr. Lincecum's emphatic assurance that he has witnessed the fact. His account is that the seed of the ant-rice, which is a biennial plant, is sown in time for the autumnal rains to bring up. At the beginning of November a green row or ring of ant-rice, about four inches wide, is seen springing up round the circumference of the disk. In the vicinity of this circular ring the ants do not permit a single spire of any other grass or weed to remain a day, but leave the aristida, or ant-rice, untouched until it ripens, which occurs in June of the next year. After the maturing and harvesting of the seed, the dry stubble is cut away and removed from the pavement or disk, which is thus left unencumbered until the ensuing autumn, when the same species of grass again appears as before, and so on. Lincecum says he has seen the process go on year after year on the same ant-farms, and adds,--

There can be no doubt of the fact that the particular
species of grain-bearing grass mentioned above is
intentionally planted. In farmer-like manner the
ground upon which it stands is carefully divested of
all other grasses and weeds during the time it is
growing. When it is ripe the grain is taken care of,
the dry stubble cut away and carried off, the paved
area being left unencumbered until the ensuing autumn,
when the same 'ant-rice' reappears within the same
circle, and receives the same agricultural attention
as was bestowed upon the previous crop--and so on year
after year, as I _know_ to be the case, in all
situations when the ant's settlements are protected
from graminivorous animals.

In a second letter Dr. Lincecum, in reply to an inquiry from Mr. Darwin whether he supposed that the ants plant seeds for the ensuing crop, says:--

I have not the slightest doubt of it. And my
conclusions have not been arrived at from hasty or
careless observation, nor from seeing the ants do
something that looked a little like it, and then
guessing at the results. I have at all seasons watched
the same ant-cities during the last twelve years, and
I know that what I stated in my former letter is true.
I visited the same cities yesterday, and found the
crop of ant-rice growing finely, and exhibiting also
the signs of high cultivation, and not a blade of any
other kind of grass or weed was to be seen within
twelve inches of the circular row of
ant-rice.--(_Journ. Linn. Soc._, vol. vi. p. 30-1.)

Now, MacCook found the ant-rice growing as described, but only on some nests. Why it does not grow upon all the nests he does not understand. So far, then, as his observations go, they confirm those of Dr. Lincecum; but he does 'not believe that the ants deliberately sow a crop as Lincecum asserts;' he thinks 'that they have for some reason found it to their advantage to permit the aristida to grow upon their disks, while they clear off all other herbage;' but finally concludes 'that there is nothing unreasonable, nor beyond the probable capacity of the emmet intellect, in the supposition that the crop is actually sown. Simply, it is the Scotch verdict--"Not proven."'

The following facts with regard to 'modes of mining' are worth quoting from MacCook:--

In sinking the galleries the difficulty of carrying is
not great in a moist or tough soil, which permits the
ant to obtain goodly-sized pellets for portage. But
when the soil is light and dry, so that it crumbles
into dust as it is bitten off, the difficulty is
greatly increased. It would be a very tedious task
indeed to take out the diggings grain by grain. This
difficulty the worker overcomes by balling the small
particles against the surface of the gallery, the
under side of the head, or within and against the
mandibles. The fore-feet are used for this purpose,
being pressed against the side face, turned under, and
pushed upward with a motion similar to that of a man
putting his hand upon his mouth. The abdomen is then
swung underneath the body and the apex pressed against
the little heap of grains of dirt massed against the
under side of the mandibles, or between that and the
smooth under surface of the head. Thus the dust is
compressed into a ball which is of sufficient size to
justify deportation.

The same operation is observed in the side-galleries,
where the ants work very frequently upon their sides
or backs, precisely as I have seen colliers do in
Pennsylvania coal-mines.

The following is likewise worth quoting from the same author:--

Seeds are evidently not the only food of our
agriculturals. When the ants at disk No. 2 had broken
through the slight mud-sediment that sealed up their
gate, as described above, they exhibited a peculiar
behaviour. Instead of heading for the roads and
pressing along them, they distributed themselves at
once over the entire disk, radiating from the gate to
all points in the circumference, from which they
penetrated the jungle of grass beyond. In a moment a
large number were returning across the roads, out of
the grass, over the pavement toward the entrance. They
bore in their mandibles objects which I presently
found to be the males and females of white ants
(_Termes flavipes_), which were filling the air,
during and after the rain, in marriage flight. They
had probably swarmed just before the shower. The
agriculturals were under great excitement, and hurried
forth and back at the top of their speed. The number
of ants bearing termites was soon so great that the
vestibule became choked, and a mass of struggling
anthood was piled up around the gate. A stream of
eager insects continually poured out of the door,
pushing their way through the crowd that vainly but
persistently endeavoured to get in with their burdens.
The outcoming ants had the advantage, and succeeded in
jostling through the quivering rosette of antennæ,
legs, heads, and abdomens. Occasionally a worker
gained an entrance by dint of sheer physical force and
perseverance. Again and again would the crowd rush
from all sides upon the gate, only to be pushed back
by the issuing throng. In the meanwhile quite a heap
of termites, a good handful at least, had been
accumulated at one side of the gate, the ants having
evidently dropped them, in despair of entrance, and
hurried off to garner more.

In due time the pressure upon the vestibule
diminished, the laden workers entered more freely, and
in the end this heap was transferred to the interior.
The rapidity with which the ants were distributed to
all parts of their roads, after the first opening of
the gates, was truly surprising. I was greatly
puzzled, at the first, to know what the cause of such
a rush might be. The whole behaviour was such as to
carry the conviction that they knew accurately what
effect the rain would have, had calculated upon it,
and were acting in accordance with previous
experience. I had no doubt at the time, and have none
now, that the capturing of insects beaten down by the
rain is one of the well-established customs of these
ants. I saw a few other insects taken in, and one
milliped, but chiefly the white ants.

That very afternoon I found in a formicary which I
then opened several large colonies, or parts of one
colony of termites, nested within the limits of the
disk and quite at home. The next day numbers of the
winged white ants were found stored within the
granaries of a large formicary. There is no reason to
doubt that these insects were intended for food, in
accordance with the quite universal habit of the
_Formicariæ_.

A curious habit has been noticed by most observers to occur in many species of ant, and it is one on which Mr. MacCook has a good deal to say. The habit in question consists in the ants transporting one another from place to place. The carrying ant seizes her comrade by the middle, and hurries along with it held aloft--the ant which is carried remaining quite motionless with all her legs drawn together. Huber supposed the process to be one enjoyable to both the insects concerned, and to be performed by mutual understanding and consent; but MacCook, in common with most other observers, supposes that it is merely a rough and primitive way of communicating to fellow-workers the locality where their services are required. He says:--

Keeping these facts in mind, we have a key to the
solution of the press-gang operations which Lincecum
observed among the agriculturals, and which have been
fully described in other species. In the absence of
any common head or directory, and of all executive
officers, a change of location or any other concerted
movement must be carried forward by the willing
co-operation of individuals. At first sight, the act
of seizing and carrying off workers does not appear
like an appeal to free-will. It is indeed coercive, so
far as the first act goes. But, in point of fact, the
coercion ceases the moment the captive is set down
within the precincts of the new movement. The
carrier-ant has depended upon securing her consent and
co-operation by thus bringing her within the circle of
activity for which her service is sought. As a rule,
no doubt, the deported ant at once yields to the
influence around her, and drops into the current of
fresh enterprise, in which she moves with as entire
freedom and as independently as any other worker. But
she is apparently under no restraint, and if she so
please, may return to her former haunts.

_Certain Ants of Africa._--Livingstone says of certain ants of Africa:--

They have established themselves on the plain where
water stands so long annually as to allow the lotus
and other aqueous plants to come to maturity. When all
the ant-horizon is submerged a foot deep, they manage
to exist by ascending to little houses built of black
tenaceous loam on stalks of grass, and placed higher
than the line of inundation. This must have been the
result of experience, for, if they had waited till the
water actually invaded their terrestrial habitations,
they would not have been able to procure materials for
their aërial quarters, unless they dived down to the
bottom for every mouthful of clay.[42]

_The Tree Ant of India and New South Wales._--These ants are remarkable from their habit of forming nests only in trees. According to Col. Sykes' account, the shape of the nest is more or less globular, and about ten inches in diameter. It is formed entirely of cow-dung, which the insects collect from the ground beneath, and work into the form of thin scales. These are then built together in an imbricated manner, like tiles or slates upon the roof of a house, the upper or outer scale, however, being one unbroken sheet, which covers the whole nest like a skull-cap. Below this the scales are placed one upon another in a wavy or scalloped manner, so that numerous little arched entrances are left, and yet, owing to the imbricated manner in which the scales are arranged, the interior of the nest is perfectly protected from rain. This interior consists of a number of irregular cells, the walls of which are formed by the same process as the exterior.

In New South Wales there is another species of ant which also frequents trees, but builds within the stem and branches. In the report of Captain Cook's expedition its habits are thus described:--'Their habitations are the insides of the branches of a tree, which they contrive to excavate, by working out the pith almost to the extremity of the slenderest twig; the tree at the same time flourishing as if it had no such inmate.' On breaking one of the branches the ants swarm out in legions. Some of our native species also have the habit of excavating the interior of trees, though not on so extensive a scale.

_Honey-making Ant_ (Myrmecocystus mexicanus).--This ant is found in Texas and New Mexico. Capt. W. B. Fleeson has observed its habits, and his observations have been communicated to the Californian Academy of Sciences, and also, by Mr. Henry Edwards, to Mr. Darwin. The following are the chief points of interest in Capt. Fleeson's results:--

The community appears to consist of three distinct
kinds of ants, probably of two separate genera, whose
offices in the general order of the nest would seem to
be entirely apart from each other, and who perform the
labour allotted to them without the least encroachment
upon the duties of their fellows. These three kinds
are--

I. Yellow workers; nurses and feeders of II.

II. Yellow honey-makers; sole function to secrete a
kind of honey in their large globose abdomens, on
which the other ants are supposed to feed. They never
quit the nest, and are fed and tended by I.

III. Black workers, guards, and purveyors; surround
the nest as guards or sentinels, in a manner presently
to be described, and also forage for the food required
for I. They are much larger and stronger insects than
either I. or II., and are provided with very
formidable mandibles.

The nest is placed in sandy soil in the neighbourhood of shrubs and flowers, is a perfect square, and occupies about four or five square feet of ground, the surface of which is kept almost unbroken. But the boundaries of the nest are rendered conspicuous by the guard of black workers (III.), which continuously parade round three of its sides in a close double line of defence, moving in opposite directions. In the accompanying diagram this sentry path is represented by the thick black lines. These always face the same points of the compass, and the direction in which the sentries march is one column from south-west to south-east, and the other column from south-east to south-west--each column, however, moving in regular order round three sides of a square. The southern side of the encampment is left unguarded; but if any enemy approaches on this or any other side, a number of the guards leave their stations, and sally forth to face the foe--raising themselves on their hind tarsi on meeting the enemy, and moving their large mandibles in defiance. Spiders, wasps, beetles, and other insects, if they venture too near the nest, are torn to pieces by the guard in a most merciless manner, and the dead body of the vanquished is speedily removed from the neighbourhood of the nest--the guard then marching back to resume their places in the line of defence, their object in destroying other insects being the defence of their encampment, and not the obtaining of food.

The object of leaving the southern side of the square encampment open is as follows. While some of the black workers are engaged on duty as guard, another and larger division are engaged on duty as purveyors. These enter and leave the quadrangle by its open or southern side along the dotted line marked _a_ to the central point _c_. The incoming line is composed of individuals each bearing a burden of fragments of flowers or aromatic leaves. These are all deposited in the centre of the quadrangle _c_. Along the other diagonal _e_ there is a no less incessantly moving double line of yellow workers (I.), whose office it is to convey the supplies deposited by the black workers at _c_ to _b_, which is the gateway of the fortress. It is remarkable that no black ant is ever seen upon the line _e_, and no yellow one upon the line _a_; each keeps his own separate station, and follows his own particular duty with a steadfastness and apparent adherence to discipline that are most astonishing. The hole at _d_ seems to be a ventilating shaft; it is never used as a gateway.

Section of the nest reveals, besides galleries, a small chamber about three feet below the surface, across which is spread, like a spider's web, a network of squares spun by the insects, the squares being about 1/4 inch across, and the ends of the whole net being fastened to the earthen walls of the chamber. In each one of the squares, supported by the web, sits one of the honey-making ants (II.). Here these honey makers live in perpetual confinement, and receive a constant supply of flowers, pollen, &c., which is continually being brought them by (I.), and which, by a process analogous to that performed by the bee, they convert into honey.

Such is an epitome of the only account that the world has yet received of the habits and economy of this wonderful insect, whose instincts of military organization seem to be not less wonderful than those of the Ecitons, though in this case they are developed with reference to defence, and not to aggression. It is especially noteworthy that the black and yellow workers are believed to belong to 'two separate genera;' for if this is the case, it is the only one I can recall of two distinct species co-operating for a common end; for even the nearest parallel which we find supplied in other species of ants maintaining aphides, is not quite the same thing, seeing that the aphides are merely passive agents, like Class II., of the honey-making ant, and not actively co-operating members of the community, like Class I.

_Ecitons._--We have next to consider the habits of the wonderful 'foraging,' or, as it might be more appropriately called, the military ant of the Amazon. These insects, which belong to several species of the same genus, have been carefully watched by Belt, Bates, and other naturalists. The following facts must therefore be accepted as fully established.

_Eciton legionis_ moves in enormous armies, and everything that these insects do is done with the most perfect instinct of military organization. The army marches in the form of a rather broad and regular column, hundreds of yards in length. The object of the march is the capture and plunder of other insects, &c., for food, and as the well-organised host advances, its devastating legions set all other terrestrial life at defiance. From the main column there are sent out smaller lateral columns, the composing individuals of which play the part of scouts, branching off in various directions, and searching about with the utmost activity for insects, grubs, &c., over every log, under every fallen leaf, and in every nook and cranny where there is any chance of finding prey. When their errand is completed, they return into the main column. If the prey found is sufficiently small for the scouts themselves to manage, it is immediately seized, and carried back to the main column; but if the amount is too large for the scouts to deal with alone, messengers are sent back to the main column, whence there is immediately dispatched a detachment large enough to cope with the requirements. Insects which when killed are too large for single ants to carry, are torn in pieces, and the pieces conveyed back to the main army by different individuals. Many insects in trying to escape run up bushes and shrubs, where they are pursued from branch to branch and twig to twig by their remorseless enemies, until on arriving at some terminal ramification they must either submit to immediate capture by their pursuers, or drop down amid the murderous hosts beneath. As already stated, all the spoils that are taken by the scouts or by the detachments sent out in answer to their demands for assistance, are immediately taken back to the main column. When they arrive there, they are taken to the rear of that column by two smaller columns of carriers, which are constantly running, one on either side of the main column, with the supplies that are constantly pouring in from both sides. Each of these outside columns is a double line, the ants composing one of the two lines all running in the same direction as the main army, and the ants composing the other line all running in the opposite direction. The former are empty-handed carriers, which having deposited their burdens in the rear, are again advancing to the van for fresh burdens. Those composing the other line are all laden with the mangled remains of insects, pupæ of other ants, &c. On either side of the main column there are also constantly running up and down a few individuals of smaller size and lighter colour than the other ants, which seem to play the part of officers; for they never leave their stations, and while running up and down the outsides of the column, they every now and again stop to touch antennæ with some member of the rank and file, as if to give instructions. When the scouts discover a wasp's nest in a tree, a strong force is sent out from the main army, the nest is pulled to pieces, and all the larvæ carried to the rear of the army, while the wasps fly around defenceless against the invading multitude. Or, if the nest of any other species of ant is found, a similarly strong force, or perhaps the whole army is deflected towards it, and with the utmost energy the innumerable insects set to work to sink shafts and dig mines till the whole nest is rifled of its contents. In these mining operations the ants work with an extraordinary display of organized co-operation; for those low down in the shafts do not lose time by carrying up the earth which they excavate, but pass on the pellets to those above; and the ants on the surface, when they receive the pellets, carry them, 'with an appearance of forethought that quite staggered' Mr. Bates, only just far enough to ensure that they shall not roll back again into the shaft, and, after depositing them, immediately hurry back for more. But there is not a rigid division of labour, although the work 'seems to be performed by intelligent co-operation amongst a host of eager little creatures;' for some of them act 'sometimes as carriers of pellets, and at another as miners, and all shortly afterwards assume the office of conveyors of the spoil.' Again, as showing the instincts of co-operation, the following may also be quoted from Bates's account:--

On the following morning no trace of ants could be
found near the place where I had seen them the
preceding day, nor were there signs of insects of any
description in the thicket; but at the distance of
eighty or one hundred yards, I came upon the same
army, engaged evidently on a razzia of a similar kind
to that of the previous evening; but requiring other
resources of their instinct, owing to the nature of
the ground. They were eagerly occupied on the face of
an inclined bank of light earth in excavating mines,
whence, from a depth of eight or ten inches, they were
extracting the bodies of a bulky species of ant of the
genus Formica. It was curious to see them crowding
round the orifices of the mines, some assisting their
comrades to lift out the bodies of the Formicæ, and
others tearing them in pieces, on account of their
weight being too great for a single Eciton; a number
of carriers seizing each a fragment, and carrying it
off down the slope.

These Ecitons have no fixed nest themselves, but live, as it were, on a perpetual campaign. At night, however, they call a halt and pitch a camp. For this purpose they usually select a piece of broken ground, in the interstices of which they temporarily store their plunder. In the morning the army is again on the march, and before an hour or two has passed not a single ant is to be seen where the countless multitudes had previously covered the ground.

Another and larger species of Eciton (_E. humata_) hunts sometimes in dense armies, and sometimes in columns, according to the kind of prey of which they are in search. When in columns they are seeking for the nests of a certain species of ant which have their young in holes of rotten logs. These Ecitons when seeking for these nests hunt about, like those just described, in columns, which branch off in various directions. When a fallen log is reached, the column spreads over it, searching through all the holes and cracks. Mr. Belt says of them:--

The workers are of various sizes, and the smallest are
here of use, for they squeeze themselves into the
narrowest holes, and search out their prey in the
furthest ramifications of the nests. When a nest of
the _Hypoclinea_ is attacked, the ants rush out,
carrying the larvæ and pupæ in their jaws, but are
immediately despoiled of them by the Ecitons, which
are running about in every direction with great
swiftness. Whenever they come across a _Hypoclinea_
carrying a larva or pupa, they take it from it so
quickly, that I could never ascertain exactly how it
was done.

As soon as an Eciton gets hold of its prey, it rushes
off back along the advancing column, which is composed
of two sets, one hurrying forward, the other returning
laden with their booty, but all and always in the
greatest haste and apparent hurry. About the nest
which they are harrying, all appears in confusion,
Ecitons running here and there and everywhere in the
greatest haste and disorder; but the result of all
this apparent confusion is that scarcely a single
_Hypoclinea_ gets away with a pupa or larva. I never
saw the Ecitons injure the Hypoclineas themselves,
they were always contented with despoiling them of
their young.

The columns of this species 'are composed almost entirely of workers of different sizes;' but, as in the species previously mentioned, 'at intervals of two or three yards there are larger and lighter coloured individuals that often stop, and sometimes run a little backward, stopping and touching some of the ants with their antennæ,' and looking 'like officers giving orders and directing the march of the column.'

Concerning the other habits of this species, the same author writes:--

The eyes in the Ecitons are very small, in some of the
species imperfect, and in others entirely absent; in
this they differ greatly from the _Pseudomyrma_ ants,
which hunt singly and which have the eyes greatly
developed. The imperfection of eyesight in the Ecitons
is an advantage to the community, and to their
particular mode of hunting. It keeps them together,
and prevents individual ants from starting off alone
after objects that, if their eyesight was better, they
might discover at a distance; the Ecitons and most
other ants follow each other by scent, and, I believe,
they can communicate the presence of danger, of booty,
or other intelligence, to a distance by the different
intensity or qualities of the odours given off. I one
day saw a column of _Eciton hamata_ running along the
foot of a nearly perpendicular tramway cutting, the
side of which was about six feet high. At one point I
noticed a sort of assembly of about a dozen
individuals that appeared in consultation. Suddenly
one ant left the conclave, and ran with great speed up
the perpendicular face of the cutting without
stopping. It was followed by others, which, however,
did not keep straight on like the first, but ran a
short way, then returned, then again followed a little
further than the first time. They were evidently
scenting the trail of the pioneer, and making it
permanently recognisable. These ants followed the
exact line taken by the first one, although it was far
out of sight. Wherever it had made a slight _détour_
they did so likewise. I scraped with my knife a small
portion of the clay on the trail, and the ants were
completely at fault for a time which way to go. Those
ascending and those descending stopped at the scraped
portion, and made short circuits until they hit the
scented trail again, when all their hesitation
vanished, and they ran up and down it with the
greatest confidence. On gaining the top of the
cutting, the ants entered some brushwood suitable for
hunting. In a very short space of time the information
was communicated to the ants below, and a dense column
rushed up to search for their prey. The Ecitons are
singular amongst the ants in this respect, that they
have no fixed habitations, but move on from one place
to another, as they exhaust the hunting grounds around
them. I think _Eciton hamata_ does not stay more than
four or five days in one place. I have sometimes come
across the migratory columns; they may easily be
known. Here and there one of the light-coloured
officers moves backwards and forwards directing the
columns. Such a column is of enormous length, and
contains many thousands if not millions of
individuals. I have sometimes followed them up for two
or three hundred yards without getting to the end.

They make their temporary habitations in hollow trees,
and sometimes underneath large fallen trunks that
offer suitable hollows. A nest that I came across in
the latter situation was open at one side. The ants
were clustered together in a dense mass, like a great
swarm of bees, hanging from the roof but reaching to
the ground below. Their innumerable long legs looked
like brown threads binding together the mass, which
must have been at least a cubic yard in bulk, and
contained hundreds of thousands of individuals,
although many columns were outside, some bringing in
the pupæ of ants, others the legs and dissected bodies
of various insects. I was surprised to see in this
living nest tubular passages leading down to the
centre of the mass, kept open just as if it had been
formed of inorganic materials. Down these holes the
ants who were bringing in booty passed with their
prey. I thrust a long stick down to the centre of the
cluster, and brought out clinging to it many ants
holding larvæ and pupæ, which probably were kept warm
by the crowding together of the ants. Besides the
common dark-coloured workers and light-coloured
officers, I saw here many still larger individuals
with enormous jaws. These they go about holding wide
open in a threatening manner.

It was this ant which, as previously stated, showed sympathy and fellow-feeling with companions in difficulties.

The habits of _E. drepanophora_ are closely similar to those of the species already described; and, indeed, except in matters of detail, all the species of Ecitons have much the same habits. Mr. Bates records an interesting observation which he made on one of the moving columns of this species. He says: 'When I interfered with the column or abstracted an individual from it, news of the disturbance was quickly communicated to a distance of several yards to the rear, and the column at that point commenced retreating.' The main column is in this species narrower, viz., 'from four to six deep,' but extends to a great length, viz., half a mile or more. It was this species of Eciton that the same naturalist describes as enjoying periods of leisure and recreation in the 'sunny nooks of the forest.'

Next we have to consider _E. prædator_, of which the same observer writes:--

This is a small dark reddish species, very similar to
the common red stinging ant of England. It differs
from all other Ecitons in its habit of hunting, not in
columns, but in dense phalanxes consisting of myriads
of individuals, and was first met with at Ega, where
it is very common. Nothing in insect movements is more
striking than the rapid march of these large and
compact bodies. Wherever they pass, all the rest of
the animal world is thrown into a state of alarm. They
stream along the ground and climb to the summits of
all the lower trees, searching every leaf to its apex,
and whenever they encounter a mass of decaying
vegetable matter, where booty is plentiful, they
concentrate, like other Ecitons, all their forces upon
it, the dense phalanx of shining and quickly-moving
bodies, as it spreads over the surface, looking like a
flood of dark red liquid. They soon penetrate every
part of the confused heap, and then, gathering
together again in marching order, onward they move.
All soft-bodied and inactive insects fall an easy prey
to them, and, like other Ecitons, they tear their
victims in pieces for facility of carriage. A phalanx
of this species, when passing over a tract of smooth
ground, occupies a space of from four to six square
yards; on examining the ants closely they are seen to
move, not all together in one straightforward
direction, but in variously spreading contiguous
columns, now separating a little from the general
mass, now reuniting with it. The margins of the
phalanx spread out at times like a cloud of
skirmishers from the flanks of an army. I was never
able to find the hive of this species.