3 2 ° 
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 californica. (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,. 
