33° The Two-winged Flies 



tapering at one end. Some species inhabit ants' nests, and one is suspected 

 of living parasitically in bee-hives. 



Straliomyia is a genus containing rather large conspicuous yellow-banded 

 flies with broad flattened abdomen, while Sargus, a genus whose species 

 are common, has a subcylindrical abdomen with the whole body metallic 

 green. 



• The snipe-flies, Leptidse, are a small family represented by about fifty 

 North .\merican species, including flies having no habits or structural pecu- 

 liarities appealing specially to popular interest. They are rather .slender 

 and plainly colored, and rather heavy and slow in movement. They are 



apparently all predatory in both larval 



and adult stages. The adults may be 



best found, according to Comstock, in 



low bushes and grass. The larva; live 



in the ground, in moss, or in decaying 



wood, sometimes penetrating to the 



Fig 46i.-Diagram of wing of CAryso- burrows of wood-boring insects. The 



phila thoracica (Leptida;), showing . « , ■ , 



venation. species 01 the genus Atherix deposit 



their eggs "in dense masses attached 

 to dry branches overhanging water. Not only do numerous females con- 

 tribute to the formation of these masses, but they remain there themselves 

 and die. The larva; on hatching escape into the water. " 



In the second group of Brachycera, including flies which have their anten- 

 nae composed of four or five distinct segments, there are two families, the 

 Asilidae, or robber-flies, and the Midaids, or Midas-flies. These latter resemble 

 the robber-flies in size and general appearance, but ditTer from them by having 

 the antenna rather long and clubbed at the tip. They are predaceous, 

 catching and devouring other flying insects, and the larva; of the few species 

 w-hose life-history is known are also carnivorous, and seem to have a special 

 fancy for the larvae of the great wood-boring grubs of the giant Prionus 

 beetles. Howard believes that the large species, Mydas lutcipennis, found 

 in the Southwest, mimics in coloration and general appearance for protection 

 or aggression the tarantula-killer wa.sp found commonly in this country. 



The Asilidic, or robber-flies, compose a considerable family — nearly looo 

 species occur in this country — of large, swift, hairy, ferocious-looking flies 

 which live wholly by predatory attacks on other insects. The body is usually 

 long and slender, tapering behind (Fig. 462), although in a few genera the 

 abdomen is flattened and not unusually elongate. The proboscis is strong 

 and sharp, the eyes large and keen, and the wings long and narrow and 

 capable of carrying this insect hawk swiftly and strongly in pursuit of its 

 prey. Some of the robber-flies are very large, an inch and a half or even 

 two inches long, and they do not hesitate to attack other large and strong and 



