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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.

Lateral view of a Psychodidae True Fly Larva from Mystery Creek #308 in Washington
This wild-looking little thing completely puzzled me. At first I was thinking beetle or month larva, until I got a look at the pictures on the computer screen. I made a couple of incorrect guesses before entomologist Greg Courtney pointed me in the right direction with Psychodidae. He suggested a possible genus of Thornburghiella, but could not rule out some other members of the tribe Pericomini.
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.
Troutnut is a project started in 2003 by salmonid ecologist Jason "Troutnut" Neuswanger to help anglers and fly tyers unabashedly embrace the entomological side of the sport. Learn more about Troutnut or support the project for an enhanced experience here.

Mayfly Species Heptagenia flavescens

Where & when

In 27 records from GBIF, adults of this species have mostly been collected during June (41%), May (30%), July (11%), and April (11%).

In 22 records from GBIF, this species has been collected at elevations ranging from 618 to 5020 ft, with an average (median) of 3117 ft.

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: 9-13 mm
Wing length: 11-15 mm

A large yellowish species; a broad reddish brown dorsal band on abdominal tergites; genitalia of the flavescens type (see fig. 94).

Head yellowish; vertex ferruginous; antennal filament dusky, paler at tip; eyes bright greenish yellow, in living insect. Thorax largely ferruginous dorsally, the mesonotum shaded with blackish anteriorly, on scutellum and anterior to it. Pleura largely yellowish with reddish brown shading; sternum similar. Fore legs pale ferruginous; femora with a median and apical darker band; tibiae at apex, tips of tarsi and tarsal joinings, fuscous. Basal joint of fore tarsus about 1/4 as long as the second. Middle and hind legs yellow; femora fuscous apically; tips of tarsi and tarsal joinings somewhat dusky. Basal joint of hind tarsus distinctly shorter than the second. Wings hyaline; a pale ferruginous cloud in the costo-apical region. “Veins and cross veins moderate, subequal, fuscous, except the three costal veins which are coarse, yellowish on their basal two-thirds, fuscous on their terminal one-third, where the cross veins also are coarse, the oblique basal cross vein being always very coarse; halfway to the tip the second costal vein is always thickened and obfuscated for the length of half a millimeter, sometimes obviously, sometimes indistinctly.” (Walsh). Basal costal cross veins faint.

Abdomen yellowish, with a broad reddish-brown dorsal band on the tergites, becoming yellowish red on the apical ones. Lateral margins of all tergites pale, and on the basal and middle ones are pale submedian oblique markings from the anterior margin; posterior margins of tergites 1-6 darker. Sternites pale greenish or yellowish white, the apical ones more yellow. Segments 1-6 semi-hyaline, 7-10 opaque. Forceps pale, the tips fuscous; tails whitish; joinings reddish brown in distal portion, often pale at extreme base, and in intermediate portion alternately pale and reddish. Penes rather widely spreading apically; two large somewhat conical median spines.

This species is most nearly allied to H. cruentata (now a synonym of Raptoheptagenia cruentata), but it is considerably larger; the fuscous apical portion of the costal veins, the faint basal costal cross veins and coarse apical ones, and the lack of prominent banding on the tibiae distinguish it from that species.

Start a Discussion of Heptagenia flavescens


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