3io 



ENTOMOLOGY 



important from an economic standpoint, particularly the Ich- 

 neumonidae, of which more than ten thousand species are al- 

 ready known. Our most conspicuous ichneumonids are the 

 two species of Tkalessa, T. atrata and T. lunator (Fig. 271), 

 with their long ovipositors (three inches long in lunator, and 



FIG. 271. 



Oviposition of Thalessa lunator. Natural size. After RILEY. 



four to four and three quarters inches in atrata). Thalessa 

 bores into the trunks of trees in order to reach the burrows of 

 another large hymenopteron, Tremex columba (Fig. 31), upon 

 whose larvae the larva of Thalessa feeds. 



The enormous family Braconidae, closely related to Ichneu- 

 monidae, is illustrated by the common Apanteles congregatus, 

 which lays its eggs in the caterpillars of various Sphingidae. 

 The parasitic larvae feed upon the blood and possibly also the 

 fat-body of their host, and at length emerge and spin their co- 

 coons upon the exterior of the caterpillar (Fig. 272), sometimes 

 to the number of several hundred. Species of Aphidius trans- 

 form within the bodies of plant lice, one to each host, and the 

 imago cuts its way out through a circular opening with a cor- 

 respondingly circular lid. Chalcididae, of which some four 

 thousand species are known, are usually minute and parasitic; 



