CHAPTER XXIV 



ORDER STREPSIPTERA* 



The Stylopids or Twisted-winged Insects 



The members of this order are small, endoparasitic insects, which prey 

 on other insects. Only the males are winged; in this sex, the fore wings 

 are reduced to club-shaped appendages; the hind wings are large com- 

 pared with the size of the tiny body, fan-shaped, furnished with radiating 

 wing-veins, and folded longitudinally when at rest. The adult female is 

 larviform and legless. The mouth-parts are vestigial or wanting; the 

 alimentation is probably by osmosis. Both sexes undergo a hyper- 

 metam orphosis . 



The order Strepsiptera comprises insects that were formerly 

 classed as a family of the Coleoptera, the Stylopidas; for this reason, 

 these insects have been known as the stylopids. Recently since the 

 establishment of the order Strepsiptera, the name the twisted-winged 

 insects, derived from the technical name of the order, has been pro- 

 posed for them; but the old name is less cumbersome, and will prob- 

 ably continue to be used. 



The stylopids are small insects which live parasitically within the 

 bodies of other insects, chiefly bees, wasps, digger wasps, and certain 

 Homoptera. Their small size and the fact that nearly their entire 

 existence is passed within the bodies of their hosts result in their 

 being rarely seen except by those who are searching for them. During 

 the first stadiiim the young larvae of both sexes are free, and the adult 

 winged male leads a free existence for a brief period; but only the 

 most skilled collectors are likely to observe these minute creatures 

 during these periods, the only free stages of their 

 existence. 



The stylopids are most easily found by examin- 

 ing adult individuals of the species of insects that 

 they infest, in which may be found adult females 

 and male pupae of the parasites. The presence of a 

 stylopid is indicated by the projecting of the head 

 end of the body from between two of the abdominal 

 segments of the host (Fig. 670). Frequently a single 

 host will contain several parasites. A female Polistes 

 with eleven male stylopids has been recorded. If 

 this projecting part of the parasite is a flat disk-like 

 plate, it is the head end of a female; but if it is the 

 rounded and tuberculate end of a cylindrical body, 

 it is the head end of the pupariimi of a male. Adult 

 male stylopids can be bred by keeping alive stylo- 

 pized insects containing male pupse. 



Fig. 670. — Abdo- 

 men of stylo- 

 pized insect: s, 

 s, stylopids. 



*Strepsiptera : strepsis (ffrpexpis), a turning; pteron (irrepSv), a wing. 



(546) 



