24 
THE PAN-PACIFIC ENTOMOLOGIST 
Fig. 3. Distribution map of E. infrequens and E. inermis. 
and the coastal streams of Oregon, Washington and British Columbia 
to 4,000-10,000 ft. in the rest of western U.S. and Canada. They are 
less tolerant of silt than E. inermis and may be abundant in streams at 
high elevations. 
Larvae of E. inermis may be found in a wide variety of streams from 
sea level to 7,000 ft. in western North America, but are generally more 
abundant in clear rather than silty water (Allen and Edmunds, 1965). 
These larvae occur in a wide range of current speeds that include 
currents slower than those suitable for E. infrequens. They also 
appear able to tolerate a broader temperature range than E. infrequens 
and are frequently found in cool streams at lower elevations. Larvae 
inhabit a wide range of substrate types and are commonly found on 
various sized rocks and pebbles in midstream and on rocks and vege- 
