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.
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.
The best evidence that wasps depend upon a knowledge of the place in returning to their nests is given by the pains they take to acquire that knowledge. When Sphex ichneumonea was ready to dig her nest, she had great difficulty in finding a place that suited her. Many a spot was merely looked at and passed by, while others that seemed more attractive were left after they had been excavated for a little way. At last, the nest dug, she was ready to go out and seek for her store of provisions; and now came a most thorough and systematic study of the surroundings. The nests that had been partly made and then deserted had been left without any circling. Evidently she was conscious of the difference and meant, now, to take all necessary precautions against losing her way. She flew in and out among the plants, first in narrow circles near the surface of the ground, and now in wider and wider ones as she rose higher in the air, until at last she took a straight line and disappeared in the distance. Very often, after one thorough study of the topography of her home has been made, a wasp goes away a second time with much less circling or with none at all.
If the examination of the objects about the nest makes no impression upon the wasp, or if it is not remembered, she ought not to be inconvenienced nor thrown off her track when weeds and stones are removed and the surface of the ground is smoothed over; but this is just what happens. Aporus fasciatus entirely lost her way when we broke off the leaf that covered her nest, but found it, without trouble, when the missing object was replaced. All of the species of Cerceris were extremely annoyed if we placed any new object near their nesting-places. One Ammophila refused to make use of her burrow after we had drawn some deep lines in the dust before it. The same annoyance is exhibited when there is any change made near the spot upon which the prey of the wasp, whatever it may be, is deposited temporarily. We learned from experience how important it was not to disarrange the grass or plants on such occasions. The wasps are in many cases so prudent as to conceal their booty among the leaves; and this made it very inconvenient to keep our eyes upon the captured prey, as was quite necessary if we wished to follow it on its travels. To avoid the discomfort of lying on the ground or of twisting the neck at some impossible angle for half an hour at a time, we sometimes gently moved the intercepting objects to one side; but even such a slight change cost us dear in time and patience, as it threw the wasp out of her bearings and made it difficult for her to recover her treasure. We recall one exceedingly warm day in September when we were delayed in this way for forty minutes, when she would have seized the spider and gone on her way without a pause had we not interfered.[ill288]
