The giant Salmonflies of the Western mountains are legendary for their proclivity to elicit consistent dry-fly action and ferocious strikes.
In 10 records from GBIF, adults of this species have been collected during July (30%), August (30%), September (20%), and June (20%).
In 3 records from GBIF, this species has been collected at elevations of 2270, 2854, and 29016 ft.
Most physical descriptions on Troutnut are direct or slightly edited quotes from the original scientific sources describing or updating the species, although there may be errors in copying them to this website. Such descriptions aren't always definitive, because species often turn out to be more variable than the original describers observed. In some cases, only a single specimen was described! However, they are useful starting points.
Abdominal tergites of male imago pale yellowish white, each with a row of four minute red transverse dashes on the posterior margin on each side.
Face and thorax deep blackish brown. Thoracic sternum deep black brown; posterior margin of mesonotum and pleural sutures tinged with pale yellowish brown. Legs pale yellowish white. Wings hyaline. Hind wing long and narrow, two longitudinal veins (see fig. 165). Abdominal segments 2-6 pale yellowish white; each tergite with a lateral row of four minute red transverse dashes on each side, these dashes situated on the posterior margin of the tergite. Tergites 7-10 deep chocolate brown, sternites alabaster white; the pleural fold forms a sharp division between these two colors. A faint slightly curved hair-line of black marks the spiracular area, on the pale segments. Forceps and tails white. Inner margin of second joint of the forceps with a poorly developed inward bulge, much less apparent than in C. caliginosum (now a synonym of Procloeon caliginosum) (see fig. 166).
From the allied C. caliginosum, this species may be separated by the smaller size, and the lesser development of the bulge on the second forceps joint. The much narrower hind wing distinguishes it from C. bifurcatum (now a synonym of Anafroptilum bifurcatum).