Wasps, Social and Solitary

by George W. Peckham; E. G. Peckham

TRYPOXYLON RUBROCINCTUM

The concentration of the nervous system in the Arachnida would seem to conduce very strongly to uniform results from the stinging of the wasps. Unlike the larva used by Ammophila, with its chain of ganglia, in the Araneidæ the whole central nervous system, including the brain and the ventral cord, forms a single mass, pierced by the œsophagus. The greater part of this mass, which lies behind the œsophagus, represents the fused ventral cord from which the nerves radiate. It is evident that a thrust given in almost any part of the ventral face of the cephalothorax, or even on either side of the anterior half of its edges, would reach the nervous centre. With these facts before us let us turn to the notes made upon the condition of the spiders that had been stung and stored up in the nests of the straw-stack. By the “first cell” we mean the last one stored, which was naturally the first one opened.

July 11. Opened a nest of rubrocinctum. The first cell contained fourteen live spiders with a newly laid egg. Some of the spiders were very lively, moving spontaneously. Second cell, ten spiders, one dead, others alive, and an egg. Third cell, eight spiders, three dead and five alive, and the egg.

July 12. In each of the first and second cells one spider has died since yesterday, while in the third there is no change in their condition. The egg in the third cell hatched at nine in the morning, and the one in the second cell at three in the afternoon.

July 13. In the first cell all the spiders are dead but one, and in the second, all but four, while in the third none are alive.

July 15. All the spiders in the second cell are dead.

July 16. The one spider in the first cell has outlived all the others, but that, too, died to-day.

The record of another set of nests is as follows: On July eighth we took a straw with a wasp as she went in with her spider. The cell was not sealed up. It contained fourteen specimens of three species of orb-weavers, and the egg was apparently just laid. The spiders were pushed in very tightly, and the legs and abdomens were, in many cases, bent to one side. All were limp, but alive. By July tenth, four were dead; on July eleventh the egg hatched. By July thirteenth all of the spiders were dead.

It is unnecessary to give the history of other nests in detail, since these facts make it clear that there is a great variation in the degree of severity with which the spiders are stung, so that while with some the paralysis is complete, with others it is only partial. Some were killed outright, others lived two or three days, while still others survived for two weeks. Compared with the work of the Pelopæi it would seem that a smaller number of the spiders are killed at once, while a larger number die after the lapse of a few days. None of the victims of Trypoxylon live so long as the most perfectly paralyzed spiders of the mud-daubers. Two of them lived ten and fifteen days respectively, while with Pelopæus one survived until the thirty-eighth and one until the fortieth day.

The egg requires from forty to sixty hours for its development, and the larva feeds for seven or eight days before spinning its cocoon. Those that we watched usually disposed first of the abdomen and then of the cephalothorax; sometimes they would consume several abdomens before attacking the other parts. After the body was devoured the legs were picked up and eaten. When the supply of food was generous, portions of the spiders were sometimes left untouched. The cocoons resembled in general appearance and structure those of Pelopæus.