372 GENERAL BIOLOGY 



PARASITIC INSECTS 



"Among the insects there are many kinds that live parasitically for 

 part of their life, and not a few that live as parasites for their whole life. 

 The true sucking lice and the bird lice live for their whole lives as exter- 

 nal parasites on the bodies of their host, but they are not fixed that is, 



they retain their legs and power of locomotion, although they have lost 



IT. 



III. 

 Fig. 242. 



I. Ichneumon-fly. Natural size. 



II. Thalessa boring in an ash tree to deposit its eggs in the 

 burrow of a horntail larva, a wood borer. From photograph, 

 natural size. (After Dsrvison.) 



III. Corn root aphis (Aphis maidiradicis) , winged and wing- 

 less female. The two black processes at the rear are Cornicles. 

 (From Needham's "General Biology" by permission The Comstock 

 Pub. Co.) 



