After days passed in flying about the garden—going up Bean Street and down Onion Avenue, time and time again—one would think that any formal study of the precise locality of a nest might be omitted; but it was not so with our wasps. They made repeated and detailed studies of the surroundings of their nests. Moreover, when their prey was laid down for a moment on the way home, they felt the necessity of noting the place carefully before leaving it.
Of the species that catch their prey before making the nest we have good examples in Pompilus quinquenotatus, the tornado wasp, and fuscipennis, the Pompilus with the red girdle.
[Illustration: COURSE FOLLOWED BY POMPILUS FUSCIPENNIS IN FINDING HER SPIDER AND IN RETRACING HER STEPS TO THE NEST[5]]
The tornado wasp may make her nest anywhere from one to ten feet from the spot on which she has deposited her spider, while fuscipennis never goes more than fourteen inches away. During the process of excavation both of these wasps pay several visits to the spider, and frequently they have difficulty in finding it. As an example of this kind of trouble we give a diagram of the course followed by an individual of fuscipennis after she had finished her nest, in trying to find her spider and in bringing it home. This and the other similar diagrams that are given are reductions of large tracings that were made on the spot. Although not absolutely correct they are exact enough for all practical purposes, since wherever there is an error it is necessarily in the direction of making the path pursued by the wasp appear shorter and less complex than it really was. The individual in question had placed her spider on a cucumber vine which lay on the ground, not hidden by leaves, but fully exposed to view. The nest was only eight inches away, but when it was finished and the wasp went to bring the spider, she found it only after a search of three minutes; and then when she went back to the nest she at first passed to one side and went some inches beyond, so that she had to retrace her steps.
Marchal notes that some wasps are very unskillful in finding their way about, showing by their errors and hesitations not only that they have no sense of direction, but that they are badly served by their memory and by what senses they have. He draws this conclusion from his own observations, one of which had for its subject Pompilus seriaceus, which nests, conveniently for him, in the walls of the rustic summer–house which he uses for a laboratory. A wasp of this species, having caught her spider, had a most wearisome experience in getting it to the nest, which had been previously excavated near the ground. She first carried it straight up, not only passing the opening, but going to the very top of the wall. Realizing that she had gone wrong, she laid it down, and after a prolonged hunt up and down, to the right and to the left, found the nest; but on leaving it again to go for the spider, she started in exactly the wrong direction, down instead of up; and not until forty minutes had been spent in searching alternately for spider and for nest did she finally bring the two together.