220 NORTH AMKRICAN DIPTERA. 



eluding many genera and species. Most of the species 

 can be recognized by their spherical head, large eyes, 

 piercing proboscis, large thorax and slender legs and 

 abdomen. Some of the minute forms resemble certain of 

 the Platypezidae or smaller muscids. The members of 

 the family are for the most part modest in coloration, 

 gray, blackish or reddish; a few tropical forms are me- 

 tallic. They are all predaceous, preying upon smaller 

 flies, which they impale on their proboscis. Microphones 

 and Anthalia and their allies, are common visitors to 

 flowers. Some species of Rhamphomyia, Empis and Hilara 

 dance in the air in immense swarms. The species of Clino- 

 cera are sluggish, and may be found along the banks of 

 streams. Tachydromia runs sw r iftly over stones in search of 

 prey. Some species of Hilara and Empis construct peculiar 

 frothy balloons at mating time. The peculiar armature 

 of the legs is mostly a sexual characteristic possessed by 

 the males. Empididae are especially abundant in moun- 

 tainous, damp and woody regions during the early sum- 

 mer; they are pre-eminently a boreal group. In dry 

 regions they are rare, perhaps a result of the dominance 

 of the related but more powerful Asilidse. 



The larvae of this family are nearly cylindrical, taper- 

 ing anteriorly, with a very small and partly retracted 

 head. The abdominal segments have more or less promi- 

 nent prolegs. The larvae live in decaying vegetable mat- 

 ter or in running streams; the pupae are free. The early 

 stages of Empididae are but little known. 



TABLE OF GENERA. 



i. Anal cell wanting or incomplete; cliscal cell always united with 

 the second basal; three posterior cells; third longitudinal vein 

 simple; antennas two or three-jointed: femora often thickened 

 and mucronate below. .... Tachydromiinse. 

 Anal cell complete; or, if incomplete, the front coxae are greatly 

 lengthened; often four posterior cells; third longitudinal vein 

 often furcate. 2 



