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Artistic view of a Male Pteronarcys californica (Pteronarcyidae) (Giant Salmonfly) Stonefly Adult from the Gallatin River in Montana
Pteronarcys californica

The giant Salmonflies of the Western mountains are legendary for their proclivity to elicit consistent dry-fly action and ferocious strikes.

27" brown trout, my largest ever. It was the sub-dominant fish in its pool. After this, I hooked the bigger one, but I couldn't land it.
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Mayfly Species Epeorus dispar

Where & when

In 6 records from GBIF, adults of this species have been collected during May (50%) and June (50%).

In 8 records from GBIF, this species has been collected at elevations ranging from 981 to 2642 ft, with an average (median) of 2342 ft.

Species Range

Physical description

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.

Male Spinner

Described in Needham et al (1935) as Iron dispar
Body length: 9 mm
Wing length: 9 mm

Penes somewhat as in I. humeralis (now a synonym of Epeorus vitreus), but apical margin of forceps base different; veins brown in apical half of fore wing.

Head pale yellow-brown. Margin of clypeus, edge of median carina, and streak at inner corner of eye, purple. Small purplish dots between antennae and below base of each. Antennal filament dusky, the tip pale. Eyes much as in I. rubidus (now a synonym of Epeorus vitreus). Purple spot at median line on posterior margin of head. Thorax yellowish brown. Anterior margin of pronotum, also posterior margin at median line, purple; purplish sub-median streak on each side. Median darker streak on mesonotum, bordered by pale yellow. Scutellum dark brown. Metanotum dark brown, paler laterally. Pleura yellowish; purple streak on anterior coxa and area above it; purplish marks and two dark spots above each of other coxae. Sternum pale yellow, mesosternum brownish. Fore femur yellow-brown; rather small median purple spot, pale brown apical mark. Tibia purplish brown, darker at apex and in basal third; tarsus pale yellow, joinings widely purplish; distal joint dusky. Basal joint of fore tarsus distinctly longer than second, which is subequal to third. Middle and hind legs pale yellowish white; purplish median spot on each femur; apices of tibiae and tarsal joinings narrowly darker. Venation in apical half of fore wing light brown; in basal half, veins almost colorless; humeral cross vein black next to subcosta. Apical subcostal cross veins of hind wing, and a few marginal intercalaries very pale brown, others colorless. Stigmatic area of fore wing opaque, whitish.

Abdominal segments 2-7 semi-hyaline, yellowish white; posterior margins of tergites purplish, this band widest at median line. Purplish black mid-dorsal line on posterior portion of tergites 1-9; lateral submedian purplish streaks on each, most extensive on tergites 1 and 2, also another series of streaks nearer the pleural fold. Purplish mark near spiracular area. Segments 8-10 opaque, yellow. Sternites immaculate except for two short purple transverse bars on each side of median line at anterior margin of sternite 2. Tails dusky, faintly yellow-tinged; not darker at joinings. Penes of the I. humeralis type; no lateral spines near apex. Apical margin of forceps base as shown in fig. 105.

Distinguished from I. punctatus (now a synonym of Epeorus punctatus), which likewise lacks the lateral spines on the penes, by the paler head and thorax, more extensive abdominal markings and brown apical veins.

Start a Discussion of Epeorus dispar


  • Needham, James G., Jay R. Traver, and Yin-Chi Hsu. 1935. The Biology of Mayflies. Comstock Publishing Company, Inc.

Mayfly Species Epeorus dispar

Species Range
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