August, 1944 



Ross: Caddis Flies of Illinois 



107 



Frons slightly concave and always covered 

 with a grayish hairy mass, the anterior mar- 

 gin straight across the middle, and provided 

 with a pair of short, elevated teeth. Dorsal 

 abdominal segments with abundant flattened 

 setae. 



Adults. — Length 12-13 mm. Color pat- 

 tern brown, the mottling similar to that of 

 simulaus, fig. 393. Male with eyes small, 

 each equal to less than half the dorsal area 

 between them. Male genitalia, fig. 383: 

 tenth tergite short, declivous and hooklike 

 with a wide mesal incision; claspers with 

 second segment long, sinuate and pointed at 

 tip; aedeagus with stem straight, lateral 

 plates upturned and meeting mesal dome 

 on a line with the dorsal outline of stem, 

 lateral flanges not sharp, and the tip of the 

 plates rounded from side view, the mesal 

 cavity two-thirds closed, and the mesal 

 plates triangular and not projecting ventrad. 

 Female with ninth tergite, fig. Z%6K, very 

 similar to that of bidens; clasper receptacle 

 with anterior and posterior dorsal margins 

 usually of about equal slope. 



This species is one of the most common 

 along the larger rivers and has been taken 

 quite generally in Illinois. Especially heavy 

 flights have been seen along the Rock, Illi- 

 nois and Mississippi rivers. Adult emer- 

 gence continues from April to September. 



The range of the species, fig. 14, covers 

 the central Corn Belt states and widens 

 toward the south to include most of the 

 Gulf Coast states. We have records from 

 Alabama, Arkansas, Georgia, Illinois, Indi- 

 ana, Iowa, Kentucky, Michigan, Minnesota, 

 Ohio, Tennessee, Texas and Wisconsin. 



Illinois Records. — Many males and fe- 

 males and six pupae, taken April 24 to Oc- 

 tober 2, and many larvae, taken April 24 

 to July 23, are from Alton, Cairo, Chicago, 

 Dixon, East Dubuque, Eddyville (Lusk 

 Creek), Elgin (Botanical Gardens), Eliza- 

 bethtown, Florence, Golconda, Grafton 

 (Mississippi River), Grand Tower, Ham- 

 ilton, Harrisburg, Havana (Spoon River), 

 Herod, Homer (Salt Fork River), Horse 

 Shoe Lake, Jerseyville, Kankakee, Keiths- 

 burg, Meredosia, Milan (Rock River), Mo- 

 mence (Kankakee River), Mount Carmel, 

 New Boston, Oakwood (Salt Fork River), 

 Oregon (Castle Rock), Ottawa, Putnam 

 (Lake Senachwine), Quincy, Rockford, Rock 

 Island, Rosiclare, St. Joseph, Savanna, 

 Shawneetown, Sterling, Urbana, White 

 Pines Forest State Park. 



Hydropsyche bidens Ross 



Hy dropsy che bidens Ross (1938rt, p. 142); 



&, 9. 



Larva. — Not definitely reared; we have 

 some statistical evidence that it might be 

 similar to that of orris. 



Adults. — Length 10-11 mm. Color 

 brown, mottled as in simulans. Male with 

 eyes small, each slightly smaller than half 

 the dorsal area between them. Male geni- 

 talia similar to those of orris in structure 

 of tenth tergite and claspers, differing chief- 

 ly in the shape of the aedeagus, fig. 382, 

 which has the lateral plates parallel with 

 the axis of the stem, the lateral flanges 

 sharp and almost pointed at apex, and the 

 mesal dome rounded and curving consider- 

 ably ventrad to meet the apex of the lateral 

 plates. Female ninth tergite, fig. 386L, very 

 similar to that of orris. Extreme care must 

 be exercised in identifying females of bidens, 

 orris, simulans and incommoda. The differ- 

 ences between them are relative and subject 

 to variation. For this reason, females of 

 this group should not be used for isolated 

 records. 



This species is distributed over the entire 

 state. It has been taken along a large vari- 

 ety of streams, ranging from small creeks 

 to large rivers. Most of our collections have 

 been of a few specimens, but occasionally 

 large flights have been encountered. Adult 

 emergence occurs from April to September. 

 The species has been taken throughout most 

 of the Corn Belt states, including Illinois, 

 Indiana, Iowa, Michigan, Minnesota, Mis- 

 souri, Ohio and Wisconsin. 



Illinois Records. — Many males and fe- 

 males, taken April 24 to September 25, are 

 from Alton, Apple River Canyon State 

 Park, Carmi, Champaign, Charleston, Dan- 

 ville, Deer Grove (Green River), Dundee, 

 East Dubuque, Elgin (Botanical Gardens, 

 Rainbow Springs), Elizabethtown, Freeport, 

 Fulton, Grafton (Mississippi River), Har- 

 din, Havana, Homer, Kampsville, Kankakee 

 (Kankakee River), Kankakee River at Illi- 

 nois-Indiana state line, Marengo, Mere- 

 dosia, Momence (Kankakee River), Mount 

 Carmel, New Boston, New Memphis (Kas- 

 kaskia River), Oakwood, Pere Marquette 

 State Park, Pike, Pontiac, Quincy (Burton 

 Creek), Richmond, Rockford, Rock Island, 

 St. Marie, Savanna, Spring Grove, Urbana, 

 Venedy Station (Kaskaskia River). 



