Mental Evolution in Man: Origin of Human Faculty

by George John Romanes

Turning now to ants, the extent to which the power of communicating by signs is here carried cannot fail to strike us as highly remarkable. In my work on Animal Intelligence I have given many observations by different naturalists on this head, the general results of which I will here render.

When we consider the high degree to which ants carry the principle of co-operation, it is evident that they must have some means of intercommunication. This is especially true of the Ecitons, which so strangely mimic the tactics 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-organized host advances, its devastating legions set all other terrestrial life at defiance. From the main column there are sent out smaller lateral columns, the component 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 despatched a detachment large enough to cope with the requirements.... On either side of the main column there are 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 wasps’-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 the pellets to those above; and the ants on the surface, when they receive the pellets, carry them—with an appearance of forethought which quite staggered Mr. Bates—only just far enough to insure 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 (or merely mechanical) division of labour: the work seems to be performed by intelligent co-operation amongst a host of eager little creatures; for some of them act at one time as carriers of pellets, and at another as miners, while all shortly afterwards assume the office of conveyers of the spoil.”[60]

Mr. Belt writes:—“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 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.... On gaining the top of the cutting, the ants entered some brushwood suitable for hunting. In a very short time the information was communicated to the ants below, and a dense column rushed up in search of prey.”

Again, Mr. Bates writes:—“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.”

On arriving at a stream of water, the marching column first endeavours to find some natural bridge whereby to cross it. Should no such bridge be found, “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 thereon. The hinder rows push the front ones farther 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 pull the bits of wood into the water, and work at enlarging the ferry-boat until it breaks again. This is repeated as long as an ant remains on shore.”[61]

So much, then, to give a general idea of the extent to which co-operation is exhibited by Ecitons—a fact which must be taken to depend upon some system of signs. Turning next to still more definite evidence of communication, Mr. Hague, the geologist, writing to Mr. Darwin from South America, says that on the mantel-shelf of his sitting-room there were three vases habitually filled with fresh flowers. A nest of red ants discovered these flowers, and formed a line to them, constantly passing upwards and downwards between the mantel-shelf and the floor, and also between the mantel-shelf and the ceiling. For several days in succession Mr. Hague frequently brushed the ants in great numbers from the wall to the floor, but, as they were not killed, the line again reformed. One day, however, he killed with his finger some of the ants upon the mantel-shelf. “The effect of this was immediate and unexpected. As soon as those ants which were approaching arrived near to where their fellows lay dead and suffering, they turned and fled with all possible haste. In half an hour the wall above the mantel-shelf was cleared of ants. During the space of an hour or two the colony from below continued to ascend until reaching the lower bevelled edge of the shelf, at which point the more timid individuals, although unable to see the vase, somehow became aware of the trouble, and turned without further investigation; while the more daring advanced hesitatingly just to the upper edge of the shelf, when, extending their antennæ and stretching their necks, they seemed to peep cautiously over the edge until they beheld their suffering companions, when they too turned and followed the others, expressing by their behaviour great excitement and terror. An hour or two later the path or trail leading from the lower colony to the vase was entirely free from ants.... A curious and invariable feature of their behaviour was that when an ant, returning in fright, met another approaching, the two would always communicate; but each would pursue its own way, the second ant continuing its journey to the spot where the first ant had turned about, and then following that example. For some days after this there were no ants visible on the wall, either above or below the shelf. Then a few ants from the lower colony began to reappear; but instead of visiting the vase, which had been the scene of the disaster, they avoided it altogether, and, following the lower front edge of the shelf to the tumbler standing near the middle, made their attack upon that with precisely the same result.”

Lastly, Sir John Lubbock made some experiments with the express purpose of testing the power of communication by ants. He found that if an ant discovered a deposit of larvæ outside the nest, she would return to the nest, and, even though she might have no larvæ to show, was able to communicate her need of assistance—a number of friends proceeding to follow her as a guide to the heap of larvæ which she had found.

In one very instructive experiment Sir John arranged three parallel pieces of tape, each about two and a half feet long: one end of each piece of tape was attached to the nest, and the other dipped into a glass vessel. In the glass at the end of one of the tapes he placed a considerable number of larvæ (300 to 600): in the glass at the end of another of the pieces he put only two or three larvæ, while the third glass he left empty. The object of the empty glass was to see whether any of the ants would come to the glass under such circumstances by mere accident. He then took two ants, one of which he placed in the glass with the many larvæ, and the other in the glass with the few. Each ant took a larva, carried it to the nest, then returned for more, and so on. After each journey he put another larva in the glass with the few larvæ, in order to replace the one which had been removed. The result of the experiment was that during 47½ hours the ants which had gone to the glass containing numerous larvæ brought 257 friends to their assistance, while during 53 hours those which had gone to the glass containing only two or three larvæ brought only 82 friends; and no single ant came to the glass which contained no larva. Now, as all the glasses were exposed to similar conditions, and as the roads to the first two must, in the first instance at all events, have been equally scented by the passage of ants over them, these results appear very conclusive as proving some power of definite communication, not only that larvæ are to be found, but even where the largest store is to be met with.

As to the means of communication, or method of sign-making, there can be no doubt that this in ants, as in bees, is mainly gestures made by the antennæ; but that gestures of other kinds are also employed is sufficiently well proved by the following observation of the Rev. Dr. M’Cook. “I have seen an ant kneel down before another and thrust forward the head, drooping quite under in fact, and lie there motionless, thus expressing as plainly as sign-language could, her desire to be cleansed. I at once understood the gesture, and so did the supplicated ant, for she at once went to work.”