318 



APPLIED ENTOMOLOGY 



ical in form. These are usually found under logs and in ants' nests and 

 may easily be mistaken for rather peculiar snails. 



Though the adults consume pollen, their visits to flowers are valuable 

 to man for the cross-pollination and the resulting "setting" of seed. 

 The insect-eating larvae often destroy enormous numbers of insect 

 pests, and the filth-inhabiting forms are at least cleaning up decay- 

 ing matter, which is generally considered desirable. On the other hand, 

 some are injurious by boring into the bulbs of cultivated plants, and sev- 

 eral species cause myiasis in man and some of the domestic animals, these 

 insects in one way or another entering the body and passing through their 

 larval development there. 



Family (Estridae (The Bot Flies). — The bot flies in their early stages 

 are parasites on mammals. The adults are of medium to large size, 

 with rather stout, thick-set bodies and frequently with reduced mouth- 

 parts, not feeding in this stage (Fig. 334). Though the group is not a 

 large one, its members are included among the more important pests of 

 domestic as well as of other animals. The parasitic part of the life of 

 these insects is in some species spent in the stomach (Fig. 335) or intes- 

 tines, in others in the pharynx or nasal cavities and frontal sinus, while 

 others live under the skin. 



Fig. 3.37. 

 Real length shown by hair 



Fig. 336. 



Fig. 336.— Ox Warble Fly {Hypoderma lineata Vill.) 

 line. (From U. S. D. A. Div. Ent. Circ. 25.) 



Fig. 337. — Full-grown Warble (larva), dorsal view (left) and side view (right) 

 Real length shown by hair line. (From U. S. D. A. Div. Ent. Circ. 25.) 



The Ox Warbles {Hypoderma lineatum, Vill. and Hypoderma hovis De 

 G.). — These two insects, both natives of Europe, are present in this 

 ocuntry, the former widely distributed, the latter most abundant in 

 Canada and a few of the Northern States. The adult fly (Fig. 336) is 

 about half an inch long. The eggs of both species are laid on the hairs of 



