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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 Isonychia obscura (Slate Drakes)

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

Body length: 12 mm
Wing length: 11 mm

A dark purplish brown species, with dark venation. Head and thorax dark purplish brown. Antenna dark purplish; purplish spots below the antennae. Purplish red spot at center of frontal margin. Lateral margins of pronotum and marks on pleura, somewhat paler. Lavender streak anterior to wing roots. Scutella black. Fore leg very dark purplish brown, tarsus slightly lighter than femur and tibia; base of femur light brown. Middle and hind legs white with greenish tinge; tarsal joinings narrowly purplish grey. Wings hyaline, venation dark purplish. Stigmatic area rather opaque white. Several stigmatic cross veins are forked.

Abdomen purplish brown, lighter in color ventrally. The anterior portion of each tergite is light brown, and a pale median dorsal streak extends the length of the abdomen. Posterior margins of all segments widely dark purplish brown. Dark submedian streaks margin the pale mid-dorsal area in the anterior portion of each tergite; from the dark posterior margin arise dark lateral streaks, rather diffuse. Pleural fold margined with purple. Ventrally, sternites 2-6 purplish rose, 7-9 a lighter shade of the same color. A wide cream margin parallels the pleural fold, and a narrow median pale line is bordered by wide purplish submedian streaks. A dark purplish brown streak, at its anterior end a dark dot, lies close to the pleural fold in the pale lateral area. Tails very dark purplish brown in the basal half, light grey distally; joinings reddish lavender. Forceps base dark reddish brown; forceps purplish brown. Forceps base very shallowly excavated apically; penes of the Isonychia arida type (see fig. 124).

Start a Discussion of Isonychia obscura


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

Mayfly Species Isonychia obscura (Slate Drakes)

Species Range
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