I20 INSECTS 



hole through an empty skin as a reminder of the tragedy. 

 Such parasites not only kill the individual, but at once 

 stop all reproduction, so that every infested louse is 

 at once eliminated as a factor in the increase of the 

 species. 



There are several families of these parasitic wasp- 

 lets; there is an enormous number of species, often of 

 the most bizarre type of structure and with extreme 

 diversity in habits. Some species remain within the 

 body of their host until they emerge as adults, often 

 giving no indication of infestation; others, when fully 

 grown, bore out through the skin and form little white 

 cocoons on the surface. Some 

 of the large Sphinx caterpillars 

 or horn-worms are often cov- 

 ered with so many of these 

 Fig. 59.— Sphinx caterpillar little cocoons as to make them 



covered with cocoons of para- . . . ^ a i 



sites. conspicuous objects. And 



not infrequently the farmer or 

 gardener carefully destroys these particular specimens, 

 because, in his opinion, they are covered with eggs — 

 forgetting the fact that a caterpillar is incapable of re- 

 production until it has first become a butterfly or moth. 



A few species, usually those feeding on borers, are 

 external feeders, the parasitic larva clinging to the 

 outside of its host and sucking its juices through a 

 small opening in the skin. 



Some parasites proclaim their character by an ex- 

 ternal protruding ovipositor or egg-laying tube, while 

 others have it modified into a sting-like organ. The 

 sting throughout the Hymenoptera is nothing more 

 than a modified ovipositor, and that explains why 

 only females of bees, wasps, ants, etc., have it. When 

 the ovipositor is external and extended, it varies greatly 

 in length. Sometimes it is short and rigid, almost 



