25150) ENTOMOLOGY 
important from an economic standpoint, particularly the Ich- 
neumonidee, of which more than ten thousand species are al- 
ready known. Our most conspicuous ichneumonids are the 
two species of Thalessa, T. atrata and T. lunator (Fig. 271), 
with their long ovipositors (three inches long in Jnunator, and 
Fic. 271. 
Oviposition of Thalessa lunator. Natural size.—After RI ery. 
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, 7reme.x columba (Fig. 31), upon 
whose larve the larva of Thalessa feeds. 
The enormous family Braconidz, closely related to Ichneu- 
monidze, is illustrated by the common A panteles congregatits, 
which lays its eggs in the caterpillars of various Sphingide. 
The parasitic larvee 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. Chalcididee, of which some four 
thousand species are known, are usually minute and parasitic ; 
