3 1 4 The Two-winged Flies 



larval life (under favorable conditions of temperature and food-supply), the 

 larva spins a little silken cornucopia-like cocoon (Fig. 426) fastened to the 

 rock by the little end, and often fastened by the sides to adjacent cocoons. 

 The large free end is left open. In this cocoon it pupates, and after about 

 three weeks the winged fly issues. The eggs are laid in patches on the rocks 



l.md. 



FIG. 420. Longitudinal section of head of old larva of black-fly, Simulium sp., showing 

 adult mouth-parts developing inside of or corresponding with the larval mouth- 

 parts, l.md., larval mandible; l.ntx., larval maxilla; I.H., larval labium; I.e., larval 

 cuticle; /.a., larval antenna; i.md., adult mandible; i.mx., adult maxilla; Hi., adult 

 labium; i.d., adult hypoderm (cell-layer of skin); i.a., adult antennae; i.e., adult 

 eye. (Much enlarged.) 



just below the surface of the water, or on the spray-dashed sides of boulders 

 in the stream or on its margin. 



In the same places where the Simulium larvae live, that is, on the smooth 

 rock faces of stream bed and lip of fall under the thin apron of swift silver 

 water of mountain streams, live also the curious flattened larvae (Fig. 430) of 

 the net-winged midges or Blepharoceridae. This small family of interesting 

 flies, comprising only eighteen species in the whole world, of which seven 

 belong to this country, is one with which the general collector will hardly 

 become acquainted unless he takes particular pains to do so. But the pains 

 are well worth while, for they are not pains at all, but pleasures. In the first 

 place, the larvae and they must be looked for first, the winged flies being very 

 rare, very retiring, and hardly distinguishable, until captured, from a number 

 of other common and less interesting kinds live only in the most attractive 

 parts of the most attractive mountain brooks. I have found them in a tiny 

 swift stream near Quebec, in two or three hillside brooks near Ithaca, 

 N. Y., in roaring mountain torrents in the Rocky Mountains, and in similar 

 plunging streams in the Sierra Nevada and Coast Range. Clinging by a 

 ventral series of six suckers to the smooth shining rock bed, the short broad 



