218 U. S. NATIONAL MUSEUM BULLETIN 216 



rather than cocoons of caterpillars as hosts. As in Iseropus, several 

 larvae develop in a single cocoon. Zaglyptus selects the egg nest of 

 a spider in which the female stays with the eggs to guard them. 

 The Zaglyptus stings the mother spider to death, then lays several 

 eggs on the batch of spider eggs. Its larvae consume the eggs and 

 usually also the body of the dead spider. Sometimes the parasite eggs 

 are laid on the body of the spider as well as on its eggs. Schizopyga, 

 which is a primitive polysphinctine, selects as host a nest-inhabiting 

 spider. The nest is invaded, the spider stung, and a parasite egg 

 laid on the body of the spider. The more specialized polysphinctines 

 oviposit on free-living spiders. The chain between parasites on larvae 

 in plant tissues, larvae in cocoons, spider-egg cocoons, both spider- 

 egg cocoons and their guarding parent, the spider itself in its egg 

 nest, and free-living spiders of various ages is practically complete, 

 with Zaglyptus at the transition point between parasites of spiders 

 or of their eggs. Zaglyptus is also somewhat transitional between 

 the two tribes in lacking the areolet, which has caused many authors 

 to classify species of Zaglyptus in the genus Polysphincta. We place 

 Zaglyptus in the Pimplini, however, because of the shape of the 

 ovipositor and because the larval structure and biology are more 

 like that of Tromatobia. 



Clistopyga is a genus placed sometimes in the Polysphinctini. It 

 lacks the areolet and has a long-tapered ovipositor like the Poly- 

 sphinctini. It does not have the tarsi swollen at the apex, however, 

 the ovipositor surface is rough rather than smooth, and according 

 to Nielsen's account of the biology and the larval morphology, these 

 resemble those of Tromatobia and Zaglyptus. On the strength of 

 these characters, we classify Clistopyga with the Pimplini rather than 

 with the Polysphinctini. 



The larvae of Tromatobia, Zaglyptus, and Clistopyga have median 

 dorsal tubercles which have paired groups of small hooks. These 

 tubercles with their hooks enable the larvae to move about in the 

 silk of spider egg cocoons. Mature larvae of Polysphinctini have 

 similar dorsal tubercles, but the tubercles themselves are paired rather 

 than single on each segment, apparently the result of subdivision of 

 the single tubercle of Tromatobia and Zaglyptus. The tubercles of 

 the polysphinctine larva are used to cling to spider webbing while the 

 cocoon is being spun, so serve a function somewhat similar to that 

 of the single tubercles of Tromatobia, Zaglyptus, and Clistopyga. 



It is relatively common to find spiders with a polysphinctine larva 

 attached to the base of the abdomen. American workers have reared 

 a number of the Nearctic polysphinctines, but except for some brief 

 notes, they have left only host records as a result of their work. The 

 European species have been more extensively investigated and Niel- 



