33 ° 
The Two-winged Flies 
tapering at one end. Some species inhabit ants’ nests, and one is suspected 
of living parasitically in bee-hives. 
Stratiomyia 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, Leptidae, are a small family represented by about fifty 
North American 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 larvae live 
in the ground, in moss, or in decaying 
wood, sometimes penetrating to the 
burrows of wood-boring insects. The 
species of 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 larvae 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 Midaidae, or Midas-flies. These latter resemble 
the robber-flies in size and general appearance, but differ from them by having 
the antennae rather long and clubbed at the tip. They are predaceous, 
catching and devouring other flying insects, and the larvae of the few species 
whose 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 luteipennis , found 
in the Southwest, mimics in coloration and general appearance for protection 
or aggression the tarantula-killer wasp found commonly in this country. 
The Asilidae, or robber-flies, compose a considerable family—nearly 1000 
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 
Fig. 461. —Diagram of wing of Chryso- 
phila thoracica (Leptidae), showing 
venation. 
