In the immense realm of the invertebrates, the highest psychical development is, by general acknowledgment, met with among the social Hymenoptera; and the capital representatives of this group are the ants. To these we may confine ourselves. Despite their tiny size, their brain, particularly among the neuters, is remarkable in structure—“one of the most marvellous atoms,” says Darwin, “in all matter, not excepting even the human brain.” Injuries to this organ, which are frequent in their sanguinary combats, cause disorders quite analogous to those observed in mammals. It is useless to recall what every one knows of their habits: their organisation of labor, varied methods of architecture, their wars, plundering and rape, practice of slavery, methods of education, and (in certain species) their agricultural labors, harvesting, construction of granaries,[10] etc. We, on the contrary, must examine the exceptional cases in which the ants depart from their general habits; for their ability to abstract, to generalise, and to reason, can only be established by new adaptations to unaccustomed circumstances. The following may serve as examples:
“A nest was made near one of our tramways,” says Mr. Belt, “and to get to the trees, the leaves of which they were harvesting, the ants had to cross the rails, over which the cars were continually passing and re-passing. 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 cars 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.”
Another observer, Dr. Ellendorf, who has carefully studied the ants of Central America, recounts a similar experience. These insects cut off the leaves of trees and carry them to their nests, where they serve various purposes. One of their columns was returning laden with spoils.
“I placed a dry branch, nearly a foot in diameter, obliquely across their path, which was lined on either side by an impassable barrier of high grass, and pressed it down so tightly on the ground that they could not creep underneath. The first comers crawled beneath the branch as far as they could, and then tried to climb over, but failed owing to the weight on their heads.... They then stood still as if awaiting a word of command, and I saw with astonishment that the loads had been laid aside by more than a foot’s length of the column, one imitating the other. And now work began on both sides of the branch, and in about half an hour a tunnel was made beneath it. Each ant then took up its burden again, and the march was resumed in the most perfect order.”
They also show considerable inventiveness in the construction of bridges. It appears from numerous observations that they know how to place straws on the surface of water, and to keep them in equilibrium or unite their several ends together with earth, moisten them with their saliva, restore them when destroyed, and to construct a highway made of grains of sand, etc. (Réaumur.) They even employ living bridges: “The ground about a maple tree having been smeared with tar so as to check their ravages, the first ants who attempted to cross stuck fast. But the others were not to be thus entrapped. Turning back to the tree they carried down aphides which they deposited on the tar one after another until they had made a bridge over which they could cross the tarred spot without danger.”[11]
I shall cite no observations on the intelligence of wasps and bees, but I wish to note one rudimentary case of generalisation. Huber remarked that bees bite holes through the base of corollas when these are so long as to prevent them from reaching the honey in the ordinary way. They only resort to this expedient when they find they cannot reach the nectar from above; “but having once ascertained this, they forthwith proceed to pierce the bottoms of all the flowers of the same species.” Doubtless association and habit may be invoked here, but before these were produced, was there not an extension of like to like?
For the higher animals I shall also restrict myself to the upper types. We shall of course reject all observations relating to “performing” animals, all acquirements due to education and training by man, as also the cases in which, as in the beaver, there is a perplexing admixture of instinct so called (a specific property), and adaptation, varying according to time and place.
The elephant has a reputation for intelligence which may be somewhat exaggerated. His psychology is fairly well known. We may cite a few characteristic traits that bear upon our subject. He will tear up bamboo canes from the ground, break them with his feet, examine them, and repeat the operation until he has found one that suits him; he then seizes the branch with his trunk and uses it as a scraper to remove the leeches which adhere to his skin at some inaccessible part of his body. “This is a frequent occurrence, such scrapers being used by each elephant daily.” When he is tormented by large flies he selects a branch which he strips of its leaves, except at the top, where he leaves a fine bunch. “He will deliberately clean it down several times, and then laying hold of its lower end he will break it off, thus obtaining a fan or switch about five feet long, handle included. With this he keeps the flies at bay. Say what we may, these are both really bona fide implements, each intelligently made for a definite purpose.”
“What I particularly wish to observe,” says an experienced naturalist, “is that there are good reasons for supposing that elephants possess abstract ideas; for instance, I think it is impossible to doubt that they acquire through their own experience notions of hardness and weight, and the grounds on which I am led to think this are as follows. A captured elephant, after he has been taught his ordinary duty, say about three months after he is taken, is taught to pick up things from the ground and give them to his mahout sitting on his shoulders. Now for the first few months it is dangerous to require him to pick up anything but soft articles, such as clothes, because the things are often handed up with considerable force. After a time, longer with some elephants than others, they appear to take in a knowledge of the nature of the things they are required to lift, and the bundle of clothes will be thrown up sharply as before, but heavy things, such as a crowbar or piece of iron chain, will be handed up in a gentle manner; a sharp knife will be picked up by its handle and placed on the elephant’s head, so that the mahout can also take it by the handle. I have purposely given elephants things to lift which they could never have seen before, and they were all handled in such a manner as to convince me that they recognised such qualities as hardness, sharpness, and weight.”
Lloyd Morgan, who, in his books on comparative psychology, is evidently disposed to concede as small a measure of intelligence to animals as possible, comments upon the above observation as follows:[12]