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.” [Illustration: FIG. 20.--Spiders placed by Solitary Wasps in the crotches of branching stems (after Peckham).]