The digger wasp, for instance, seems to display highly intelligent brood-tending behavior. Having dug a nest, it flies off in search of a caterpillar, overpowers and kills it, drags it into the nest, and lays eggs on it. The emerging young are thereby provided with the nourishment they need and find protection in the nest, which the wasp seals. Interrupt the sequence of partactions, however, and it soon becomes clear that no form of intelligence is at work here. Returning to its hole with the caterpillar, the wasp first deposits it in the entrance and inspects the interior, then reappears at the entrance, head foremost, and drags its quarry inside. If, while the wasp is inspecting its hole, the caterpillar is removed and deposited some distance away, the wasp will continue to search until it has rediscovered the caterpillar and then will drag it to the entrance again, whereupon the whole cycle-depositing, inspecting, etc. – begins all over again. Take away the caterpillar ten or twenty times, and the wasp will still deposit it at the entrance and embark on a tour of the hole, with which it is thoroughly familiar by this time. The insect continues to be guided by the same commands, in computer fashion, and evidently finds it hard to make any change in the overall sequence. Only after thirty or forty repetitions will the wasp finally drag the caterpillar into its nest without further inspection. Yet the digger wasp shows a great aptitude for learning where other procedures are concerned. While in flight, it memorizes the route which it must take on the ground when returning to the nest with its prey – a very considerable feat of learning. On the other hand, the burial of its prey is an instinctive action and, thus, strongly programmed. The wasp is almost incapable of influencing or altering this part of its behavior by learning, because it is controlled by an innate and extremely incorrigible mechanism.
Once stimulated, whole cycles of action can proceed by themselves. In the squirrel, food storing consists of the following part-actions: scraping away soil, depositing the nut, tamping it down with the muzzle, covering it over, and pressing down the soil. A squirrel reared indoors will still perform these actions in full, even in the absence of soil. It carries the nut into a corner, where it starts to dig, deposits the nut in the (nonexistent) hole, rams it home with its muzzle (even though it merely rolls away in the process), covers up the imaginary hole, and presses down the nonexistent soil. And the squirrel still does all these things even when scrupulous care has been taken to ensure that it has never set eyes on a nut before or been given an opportunity to dig or conceal objects.