The famous nocturnal Hex hatch of the Midwest (and a few other lucky locations) stirs to the surface mythically large brown trout that only touch streamers for the rest of the year.
In 1213 records from GBIF, adults of this genus have mostly been collected during June (24%), July (21%), May (19%), August (17%), September (7%), and April (5%).
In 610 records from GBIF, this genus has been collected at elevations ranging from 10 to 23622 ft, with an average (median) of 3652 ft.
Diet: For most species, other aquatic insects.
Current speed: Fast
Environmental tolerance: Most species require cool water
Shelter type: No case
A good imitaiton of a Rhyacophila larva is going to catch a lot of trout in swift, bouncing stretches of stream. The same fly is going to do poorly in slow areas of the same stream.
A fly fisherman can avoid wasting time in the wrong sections of a stream by working leap-frog fashion instead of in a straight line. If he is using an imitaiton of a fast-water insect he should fish only the swift, broken currents, skipping past the slower current areas. Likewise, if he is using an imitation of a slow-water insect he should only cover the quieter pools and flats.