ASILID^J. 



193 



segments, the hypopygium and ovipositor usually promi- 

 nent. Legs strong, bristly, of moderate length, rarely 

 elongate and slender; tarsi strong; empodium bristle- 

 like (31) or wanting, the pulvilli rarely vestigial. Squa- 

 mae small. Wings when at rest lying parallel over the 

 abdomen; basal cells long; two or three submarginal 

 and five posterior (four in Townsendia and Leptoptcromyia, 

 35) cells present; first and fourth posterior and the anal 

 cells closed or open. (Figs. 73 and 74.) 



The family Asilidae, or Robber-flies is one of the larg- 

 est and best known among diptera, including about three 

 thousand species, distributed in more than one hundred 

 and fifty genera. Many of the species are conspicuous 

 for their large size, the largest measuring nearly two 

 inches in length, while the smallest known species is 

 over four millimeters. They are, perhaps, the most pre- 

 daceous of all flies in their habits. The greater part of 

 them rest upon the ground in wait for their prey, arising 

 with a quick buzzing sound when disturbed, to alight a 



short distance beyond. Some of 

 the Iyaphrinae have a striking 

 resemblance to humble bees, and 

 are usually observed resting up- 

 on foliage about the borders of 

 forests. All their food, which 

 consists wholly of other insects, 

 is caught upon the wing; their 



luckless victims when once seiz- 

 Fig. 76. Vasyltis, species; , , , , . £ 



natural size. After Kellogg. ed h Y their strong feet are pow- 

 erless to escape. Their prey is 

 usually other flies and hymenoptera, but flying beetles, 

 especially the Cicindelae, are often caught, and they are 

 known to capture and destroy large dragonflies. In one 

 instance that the writer observed, a female seized a pair 

 of her own species, and thrusting her proboscis into the 



