The Two-winged Flies 



313 



decaying seaweed, etc., and from among these this species has no doubt 

 gradually worked its way out to the very \'erge of the shore-line, becoming 

 gradually adapted in habit and structure to the conditions of its new 

 habitat. 



Besides the mosquitoes and punkies a third kind of fly assails the rod- 

 and-line lislierman, the hunter, and the camper in forests and along the streams; 

 black, stout-bodied, hump-backed, short-legged, broad-winged flies (Fig. 

 424) from one-si.xth to one-fourth of an inch long, with short but strong 

 [liercing proboscis. These are black-flies, bufTalo-gnats or turkey-gnats, as 

 they are variously called, composing the small family Simuliida;, distributed 

 dll over this country, but especially abundant in the southern states, where 

 they attack cattle so fiercely and in such great swarms that the animals are 

 driven frantic and sometimes even killed by a violent fever ijmduced by the 

 terrible biting. 



The larvas (Fig. 426) are odd, squirming, slippery, little black "worms," 

 which, clinging by the hind tip of the body, occur in den.se colonies or patches 

 on the smooth rock bed in .shallow jilaces 

 of swift streams. The lip of a fall is a 



favorite place for them. The swift- C 'i.,^' )iyp £X. }\md 

 running water constantly affords them 

 an abundant air and food sup[)ly. The 

 free or head end of the body is provided yf^' ^ ^ fe s,./; 



ii/p. 



F'f- 427- Fig. 428. 



Fig. 427— Mouth-parts of female black-fly, Simuliiim sp. !ep., labrum; hyp., hypo- 



phan'nx; md., mandible; mx., maxilla; nixp., maxillan- palpus; /(., labium; pg., 



paraglossa. (.Much enlarged. 1 

 Fig. 428.— Mouth-parls of larva of black-fly, Simuliiwi sp. lb., labrum; ep., cpipharynx; 



md., mandible; mx., ma.\illa; mxp., maxillary palpus; m.v/., maxillary lobe;' /('.. 



labium; hyp., hypophar\'nx. (Much enlarged.) 



with a conspicuous pair of freely movable brushes which collect food from 

 the water. The clinging to the rock is effected by means of silk spun 

 from the mouth, and by the skilful use of silken threads the larva; can 

 move about over the submerged rock bed without being washed away by 

 the swift water. When ready to pupate, which is after about a month of 



