|scientific name Hesperoperla pacifica |
Large, cool water streams.
Adults emerge over a two-week period from late June to early July.
Males (length = 25 mm) have paraprocts that are flattened, triangular and sharply pointed at their anteriorly directed tips, but lack spinules on Tergites 9 and 10. Females (length = 37 mm) have the subgenital plate produced over half of Sternum 9; the hind margin of the subgenital plate is slightly angular and usually has a squarish shiny spot at its apex. The nymph has anal gills but lacks an occipital ridge. The nymphal head has a yellow mark extending from the labrum to the anterior ocellus and dark brown abdominal terga.
The life cycle is three years, and the nymphal habitat is under larger rocks in regions of the stream with the swiftest current.
The species is not endangered, but as with all stoneflies, it is sensitive to organic pollution.
Nymphs are carnivorous, preying principally on mayfly nymphs and chironomid and caddis fly larvae.
In Alberta, the species is known from the Cypress Hills and Bow River. In North America, it ranges from British Columbia to California and New Mexico and east to South Dakota and Saskatchewan.
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