MALE TRYPOXYLON AWAITING THE FEMALE
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In this species the male does not always come out of the nest when the female brings a spider, the nest being enough larger than in rubrocinctum to accommodate them both comfortably. As a usual thing, however, he enters on the back of the female. The spiders brought by albopilosum are larger than those used by rubrocinctum. They sometimes bring such heavy specimens of Epeira insularis that they are carried with difficulty, the wasp alighting and dragging the spider into the hole instead of flying directly in as usual.
We watched a number of albopilosum nests during the second summer, finding them in several instances through the loud humming of the female while she was pushing the spiders into her hole. From our not very extensive study of the spiders taken by this species we are of the opinion that some are killed at the moment of capture, while others that are only paralyzed die in the nest from day to day.
Mr. W. H. Ashmead has noted that albopilosum stores its nest with aphides, but in the cases that we observed they used only spiders. There can be no mistake on this point, as we more than once took the spider from the wasp as she was entering the nest. In a recent letter Mr. Ashmead says that his notes were made in the field, and that he probably mistook some closely allied species for this one.
We are not as familiar with the habits of T. bidentatum as with those of the other two, but we have a few notes relating to the female. This little worker is the smallest of the three, and like her sisters is a confirmed spider-hunter. Once, when out among the raspberry bushes, we had the good fortune to witness a capture. The wasp seized the spider, as it rested on a leaf, by the top of the cephalothorax, and, holding it firmly, curved her abdomen under and stabbed the ventral face of the cephalothorax. All her motions were deliberate, and after the operation she delayed a moment before picking it up by a leg and flying off. We often found raspberry stems which had been filled with spiders by this wasp, but we do not know the length of time required for the development of the egg, nor how long the larva eats before pupation. The cocoon is very different in appearance from those of rubrocinctum and albopilosum, being exceedingly long, slender, and almost white, instead of short, wide, and brown. The perfect insects come out in September, and the last cocoon formed is the first one to hatch. This was also true of the cocoons of rubrocinctum formed in straws.
Years ago, when we found that many of the orb-weavers laid enormous numbers of eggs (A. cophinaria from 500 to 2000), we wondered what became of the thousands of spiderlings. An acquaintance with Trypoxylon has shown us their fate, and has given us an illustration of how closely the two groups are related. To make a very modest estimate there must have been twenty wasps at work in our straw-stack. During the six weeks which make the busiest part of their working season each of these must have stored, at the very least, thirty cells, putting an average of ten spiders into a cell. It may then be considered certain that the straw-stack, with its working surface of twelve by twenty feet, was the mausoleum of six thousand spiders, and it is very probable that twice as many were interred within its depths. It must be remembered, too, that before the spiders have grown large enough to be interesting to rubrocinctum, bidentatum has had her turn at them, and that those that are allowed to grow too large for rubrocinctum are preyed upon grade after grade, first by albopilosum and finally by Pelopæus, Pompilus, and other genera.