Animal Intelligence Part 10

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 a.s.sociated 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 pa.s.sed 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 gra.s.s 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 mult.i.tudes 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 b.a.l.l.s, 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 a.s.sistants 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 pa.s.s 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 pa.s.sed 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 pa.s.sed 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 Reaumur, 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.

Buchner, after quoting these cases, proceeds to say (_loc. cit._, p.

120),--

The ants behaved in yet more ingenious fashion under the following very similar circ.u.mstances. Herr G.

Theuerkauf, the painter (Wa.s.serthorstr. 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.'

Buchner 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 antennae, 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 pa.s.s.

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 antennae, 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 b.u.t.tress 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 pa.s.s 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 pa.s.sed. 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 pa.s.sed three or four deep; whereas excepting for this expedient they would have had to pa.s.s 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 Buchner, gives a still more wonderful account of the ingenuity of Ecitons in crossing water. This observer is Herr H. Kreplin, of Heidemuhl (Station d.u.c.h.erom), '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 Buchner, 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 _role_ 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 pa.s.sage, they travel along the bank of the river until they arrive at a flat sandy sh.o.r.e. 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 sh.o.r.e. 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 pa.s.s. 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 pa.s.sing and repa.s.sing. 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 t.i.tus Graber, 'Insects,' vol. i. p. 255.) In structure, also, the brain of an ant is in advance of that of other insects, its nearest a.n.a.logue 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 a.s.sumed 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 _manege_, 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 antennae 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 antennae.

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 antennae 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 larvae, 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 pa.s.sing through the press Sir John Lubbock has read another paper before the Linnaean 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 larvae similarly introduced.

[21] _The Naturalist in Nicaragua_, 1874, p. 26.