In the interesting pages of the works in which Dr. and Mrs. Peckham describe their investigations, there are many observations which show that wasps are capable of intelligently profiting by the experience which their instinctive behaviour places them in a position to acquire. The inherited tendencies and aptitudes pave the way for acquired modification and accommodation of behaviour. To catch and paralyze spiders, to dig and prepare a tunnelled nest, and to carry the prey to the nest, all this affords the instinctive basis; but when the observers tell us that they “have several times seen wasps enlarge their holes when a trial had demonstrated that a spider would not go in,” and even on one occasion without trial when an unusually bulky spider was brought, there is something beyond instinct; there is intelligent adjustment to special circumstances given in experience. Presumably intelligent is the habit frequently observed in one species of Pompilus, and occasionally in another, of hanging the paralyzed spider in a crotch of a branching stem, usually of bean or sorrel, where it will be safe from the depredation of ants. On one occasion Dr. Peckham, desirous of seeing the exact manner in which the victim was stung, substituted an unhurt spider for that which the wasp had paralyzed.[57] “According to the habit of its species when danger threatens, it kept perfectly quiet, and when the wasp returned it was hanging there as motionless as a piece of dead matter; but she would not touch it; she hunted all over that plant and then over several others near to it, returning continually to look again at the right spot. After five minutes she flew off in the direction of the woods to catch another spider. Why did she go to the woods? Why did she not take the one that hung there in plain view? It could not have been due to the fact that we had handled the spider, since when, on other occasions, we took one that had been paralyzed, examined it, and then returned it to the wasp, she accepted it without hesitation.... In forty minutes she came back with another spider, but, instead of taking it into the nest, she hung it upon a bean plant near by, and then proceeded to dig a new hole a few inches distant from the first. Foolish little wasp, what a waste of labour! Truly, if you are endowed with energy beyond your fellows, you are but meagrely furnished with reason.”
Fig. 20.—Spiders placed by Solitary Wasps in the crotches of branching stems (after Peckham).
Here we have the routine of instinct—the normal mode of hunting and capturing prey, the normal procedure of bringing the spider, and then making the nest, predominating over any tendency to initiate intelligent improvements. This, however, should not surprise us, in whom the force of habit is often so strong. Nor should we feel surprise at the apparently stupid tolerance some of these wasps display in presence of parasites. Bembex, which does not store and close its cell, but brings continual supplies of food to its larvæ, is not disturbed by the presence in the cell of the grubs of the parasitic fly Miltogramma. She could, we think, easily free her nest of these intruders, but she continues to bring supplies, though the parasites may absorb it all and leave her own larvæ to perish. She adapts her procedure to the new conditions, being incapable of knowing that she is feeding the enemies of her race.
Enough has now been said to show the extent and the limitations of the intelligence of such insects as the solitary wasps. It will be noticed that the acquired modifications of behaviour occur in close connection with the inherited ground-plan of instinctive procedure. We shall have occasion to note the same connection in our discussion of social behaviour in the next chapter. And we shall consider the influence of intelligence on instinct before we bring this chapter to a close.
III.—Some Results of Experiment
It is unnecessary to give a resumé of entertaining anecdotes illustrative of intelligent behaviour in the higher animals. Such anecdotes are too often the outcome of casual observations by untrained observers; and the interpretation put upon the facts frequently shows a want of psychological discrimination. Such is not the material of which science is constituted. What is needed is systematic observation conducted, so far as possible, under controlled conditions. Two things are necessary: first, to distinguish instinctive behaviour, inherited as such, from the acquired modifications or new departures due to intelligence; and secondly, to determine the method and range of intelligent procedure. These problems can only be solved in their entirety by a complete knowledge of the life-history of the animal concerned. But they may be attacked in detail by a systematic study of particular modes of behaviour, and by an investigation into their manner of origin. That this may be done with some approach to accuracy, resort must be had to experiment, which permits of observation under controlled conditions.
To ascertain, for example, how far nest-building is instinctive in birds, Mr. John S. Budgett hatched a hen greenfinch under a canary. In the following autumn he bought a caged bird, a cock, probably of the same year, and in the succeeding spring turned the pair into a large aviary, supplying such material as twigs, rootlets, dried grass, moss, feathers, sheep’s wool and horsehair. The hen soon began to build, the cock bird taking no share in the work, and finished her nest in a few days. On careful comparison it was found to resemble that of a wild greenfinch in every particular, being made of wool, roots, and moss, lined with horsehair. A second nest the aviary greenfinch built was also quite normal.
In the case of a bullfinch which Mr. Budgett reared, having obtained it when a few weeks’ old, the first nest was composed of dried grass with a little wool and hair, but without either rootlets or twigs. A second which she built was, however, quite typical, made of fine twigs and roots, and lined with horsehair; as was also a third nest.