272 



ENTOMOLOGY 



the bodies of other insects; one of the few is Braula cczca, a wingless 

 dipteron found on the body of the honey bee. 



A vast number of insects, however, undergo their larval develop- 

 ment as internal parasites of other insects, and most of these parasites 

 belong to the two most specialized orders, Diptera and Hymenoptera. 



The larvae of Bombyliidae feed upon the eggs of Orthoptera and upon 

 larvae of Lepidoptera and Hymenoptera. Tachinidae are the most 

 important dipterous parasites of other insects and lay their eggs most 

 frequently upon caterpillars; the larvae bore into their victim, develop 



FIG. 278. Megarhyssa atrata, drilling in tree trunk. Natural size. From CHARLES 



MACNAMARA. 



within its body, and at length emerge as winged insects. These parasites 

 often render an important service to man in checking the increase of 

 noxious Lepidoptera. 



The great majority of insect parasites many thousand species 

 belong to the order Hymenoptera, constituting one of the primary 

 divisions of the order. They are immensely important from an eco- 

 nomic standpoint, particularly the Ichneumonidae, of which more than 

 ten thousand species are already known. Our most conspicuous 

 ichneumonids are the two species of Megarhyssa, M. atrata (Fig. 278), 

 and M. lunator with their long ovipositors (three inches long in 

 lunator, and four to four and three-quarters inches in atrata). Mega- 

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



