394 



DIPTEKA. 



however, that in its larval state the horse-fly is useful to man, 

 as it feeds on snails and probably the larvae of other root- 

 eating insects. The larvae of other species are aquatic, living 

 under submerged objects. Walsh describes 

 a greenish transparent larva which is cylin- 

 drical, twelve-jointed, the body being most 

 slender towards the head, which is small, 

 truncate, conical, the anterior part capable 

 of extension, with short, fleshy, exarticulate 

 antennae and without ocelli. There are six 

 pairs of dorsal fleshy tubercles. On the un- 

 der side of the abdominal segments are six 

 retractile false legs, and a single anal retractile proleg. It 

 is, when disturbed, vigorous and restless, swinnning quickly, 

 often elevating the anal slit, in which the stigmata are probably 

 placed, out of the water to take in the air. The pupa is cylin- 

 drical, obtuse at the head, tapering a little posteriorly, and is 

 of a pale yellowish brown. There are six 

 tubercles at the mouth, above which are 

 the trigonate three or four-jointed antennae. 

 The abdominal segments are furnished with 

 a ring of appressed bristles directed back- 

 Fig. 315. wards, and the anal spine is large, trun- 

 cated, and terminates in six small, stout spines. T. atratus 

 Fabr. is a common species ; it is black, covered with a whitish 

 bloom, and expands nearly two inches, while the Tabanus cinctus 

 Fabr., or Orange-belted horse-fly, is smaller and less abundant. 

 Of the smaller species the Tabanus Uneola Fabr. (Fig. 315) 

 is so named from the whitish line along the abdomen. This 

 fly is our most common species, thousands of them ap- 

 pearing during the hotter parts of the summer, when the sun 

 is shining on our marshes and Western prairies ; horses and 

 cattle are sometimes worried to death by their harassing bites. 

 In cloudy weather they do not fly and they perish on the cool 

 frosty nights of September. 



Leptid.!-: Meigen. This family is easily distinguished from 

 the preceding by the simple third joint of the antennee, which 

 are provided with a simple or thickened styliform bristle. 



