76 



Illinois Natural History Survey Bulletin 



Vol. 23, Art. 1 



stem ending in a knob, with a pair of long 

 needle-like styles following the stem, and 

 another pair of styles arising from a ventral 

 complex of internal sclerites. The short 

 dorsal processes of the male genitalia are 



Fig. 278. — Psychomyia flavida, male genitalia. 



CERCUS 



\ f\ 



K 



/ (? Tergites\v\ /// 



Fig. 279. — Psychomyia nomada, male genitalia. 



Fig. 280. — Psychomyia flavida, female geni- 

 talia. 



in marked contrast to the long structures of 

 the other eastern species, nomada, fig. 279. 

 Female genitalia, fig. 280, conical with a 

 single ventral sclerite. 



This species is rare in Illinois. We have 

 collected it in only two places, along the 

 Kankakee River at Momence, and in Apple 

 River Canyon State Park, in the northeast 

 and northwest parts of the state, respective- 

 ly. Immature stages were collected in Apple 

 River Canyon State Park in one of the 

 swift rapids of the Apple River. 



The species has a very wide and extensive 

 range which almost completely encircles the 

 Great Plains. It is restricted to swift, cold 

 streams in which it is frequently taken in 

 enormous numbers. Records are available 

 for the following: Arkansas, Colorado, 

 Idaho, Illinois, Indiana, Kentucky, Michi- 

 gan, Missouri, Montana, New Hampshire, 

 New York, North Carolina, Ohio, Okla- 

 homa, Ontario, Pennsylvania, Saskatche- 

 wan, Tennessee, West Virginia, Wisconsin 

 and Wyoming. 



Illinois Records. — Apple River Can- 

 yon State Park: May 24, 1940, H. H. 

 Ross, 1 pupa; June 6, 1940, Mohr & Burks, 

 1$. Momence: June 4, 1932, Prison & 

 Mohr, 1 2 . 



HYDROPSYGHIDAE 



Unquestionably this family is the most 

 abundant caddis fly group in Illinois. Not 

 only is our fauna rich in species, but various 

 species of Hydropsychidae form the most 

 abundant faunal element in most of the 

 rivers and streams. This same condition 

 holds true for almost the entire Corn Belt. 

 By far the largest genus is Hydropsyche. 

 Next comes Cheumatopsyche; then the re- 

 maining genera contain at the most a few 

 species each. 



The adults are diverse in size, shape and 

 numerous structural characteristics. Both 

 sexes have five-segmented maxillary palpi. 

 All genera lack scutal warts, ocelli and 

 preapical spurs on the front tibiae. 



The larvae of all genera are remarkably 

 uniform in habits and appearance. They 

 are wormlike, active and pugnacious, and 

 possess rows of bushy abdominal gills, fig. 

 281. They prefer the more rapid locations 

 in streams, usually being concentrated 

 around riffles, spillways and rapids, although 

 they may also be found wherever there is 

 an appreciable current. They make a re- 



