DIPTERA 



839 



Family THEREVID^ 



The Stiletto-Flies 



With the flies of this family the head is transverse, being nearly 

 as wide as the thorax; and the abdomen is long and tapering, suggest- 

 ing the name stiletto-flies. These flies are small or of meditmi size; 

 they are hairy or bristly. The antennse are three-jointed; the third 

 segment is simple, and usually bears a terminal style ; but this is some- 

 times wanting. Three ocelli are present. The legs are slender and 

 bristly ; the empodia are wanting. 



The radial sector is three-branched, (Fig. 1082) and the last 

 branch, vein R5, terminates beyond the apex of the wing; the three 

 branches of media are separate ; the cross-vein m-cu is present ; and 

 the first anal cell is usually closed. 



2d A + Cu, 



Fig. 1082. — Wing of Thereva. 



The adult flies are predacious; they conceal themselves among 

 the leaves of low bushes or settle on the ground in sandy spots, wait- 

 ing for other insects, chiefly Diptera, upon which they prey. 



The larvce are long and slender, and the body is apparently com- 

 posed of nineteen segments. They are found in earth, fungi, and de- 

 caying wood. They feed on decaying animal and vegetable matter 

 and are said to be predacious also. The pupae are free. 



The family is a comparatively small one, including but few genera 

 and species. 



Family SCENOPINID^ 



The Window-Flies 



The window-flies are so-called because the best-known species 

 are found almost exclusively on windows; but the conclusion that 

 these are the most common flies found on windows should not be 

 drawn from this name; for such is not the case. 



