1986] Wiggins & Richardson — Onocosmoecus 205 
Larvae are shredders, vascular plant pieces and filamentous algae 
combined accounting for over 71% of the total gut content in mate- 
rial (10 LV) we sampled. Animal fragments averaged 9.7% but in 
one individual accounted for 97% of the gut content. Diatoms were 
present in small numbers in most guts, averaging 12.2%, although 
one specimen contained approximately 77 percent diatoms. Fine 
particulate organic matter averaged 6.9%. Our data contrast 
strongly with those of Winterbourn (1971) who reported only sedi- 
ment and animal fragments in the guts of this species in a lake 
habitat. 
Head widths for the last three instars have been established as 
follows (n = 204): LV, 1.62 mm (range 1.25-2.0); LIV, 1.12 mm 
(1.025-1.125); LIII, 0.725 mm. 
Range. (Fig. 14). As defined here, O. unicolor is transcontin- 
ental through northern North America, extending throughout the 
western mountains and into eastern Asia. In North America the 
species is recorded from Alaska, Alberta, British Columbia, Cali- 
fornia, Colorado, Idaho, Maine, Manitoba, Massachusetts, Michi- 
gan, Montana, Nevada, Newfoundland, New Hampshire, New 
Mexico, New York, Northwest Territories, Nova Scotia, Ontario, 
Oregon, Quebec, Saskatchewan, South Dakota, Utah, Vermont, 
Washington, Wisconsin, Wyoming, and Yukon. 
Material examined and other records. ALASKA. 24 June-27 
September. Mile 140, Hwy. 3 (CNC). Admiralty Is. (ROM). 
Anchorage (ROM). Angel Cr. (ROM). Bear Cr. (CNC). Byers Cr. 
(ROM). Chatanika R. (Oswood). Chena R. (Oswood). Chichagof 
Is. (ROM). Chilkoot R. (ROM). Circle (ROM). Delta (CNC). 
Eklutna Lk. (INHS). Etolin Is. (ROM). Fairbanks (CNC). Gle- 
nallen (ROM). Gulkana R. (ROM). Haines (ROM). Hood Bay Cr. 
(ROM). Iditarod (MCZ, USNM). Juneau (ROM). Kenai Peninsula 
(ROM). Kodiak Is. (ROM). Lk. Iliamna (ROM). Lowe (Oswood). 
Lower Summit Lk. (ROM). Moon Lk. (ROM). Palmar (USNM). 
Parks Hwy., mp. 128.5 (ROM). Port Heiden (ROM). Portage 
(CNC). Prince of Wales Is. (DGD). Reflection Lk. (ROM). Sadle- 
rochit Spring (USNM). Squirrel Cr. Cpgrd. (CAS, DGD). Steese 
Hwy., ml. 35-97.2 (ROM). Tolsona R. (ROM). Trapper Cr. (CNC). 
Turner Lk. (ROM). Ugak Bay (ROM). Umnak Is. (ROM). Upper 
Gulkana R. (INHS). Wasilla (INHS). Wrench Cr. (ROM). 
ALBERTA. 16 July-12 October. Banff (INHS, ROM, UA, 
USNM). Calgary (INHS). Canmore (ROM, UA). Coleman (UA). 
