3 20 



The Two-winged Flies 



immature stages of one moth-fly species, Pericoma calijornica, which is, so 

 far, the only North American member of this family whose life-history is 

 known. The larvae (Fig. 446), which are little slug- like creatures, one- 

 tenth of an inch long, cling by a row of eight suckers on their ventral side 

 to stones in or on the margin of the stream, where they are constantly 



FIG. 444. FIG. 445. 



FIG. 444. Diagram of wing of Dixa sp., showing venation. 

 FIG. 445. A moth-fly, Pericoma calijornica. (Much enlarged.) 



wetted by the dashing water. When ready to_ pupate the larvae crawl a little 

 higher on the stones, where only the spray will reach them, and, fixing them- 

 selves to the rock face by a gummy exudation, change to small flattish, 

 turtle-backed pupae (Fig. 446), each with a pair of club- or trumpet-shaped 

 respiratory horns on the back of the prothorax. They look indeed much 

 like dwarf net-winged midge pupae. After 

 about three weeks the adults issue and fly 



FIG. 446. FIG. 447. 



FIG. 446. Larva, ventral surface (at left), and pupa, dorsal surface (at right), of the 

 moth-fly, Pericoma californica; also enlarged prothoracic respiratory tube of pupa. 

 (Much enlarged.) 



FiG. 447. Mouth-parts of moth-fly, Psychoda sp. lb., labrum; mx., maxilla; mx.p., 

 maxillary palpus; mx.l., maxillary lobe; li., labium; pg., paraglossa; hyp., hypo- 

 pharynx. 



up into the overhanging foliage, where they spend most of their time 

 resting on the under side of the leaves. 



The largest family of nematocerous flies in point of number of species, 



