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Lateral view of a Female Hexagenia limbata (Ephemeridae) (Hex) Mayfly Dun from the Namekagon River in Wisconsin
Hex Mayflies
Hexagenia limbata

The famous nocturnal Hex hatch of the Midwest (and a few other lucky locations) stirs to the surface mythically large brown trout that only touch streamers for the rest of the year.

Dorsal view of a Pycnopsyche guttifera (Limnephilidae) (Great Autumn Brown Sedge) Caddisfly Larva from the Yakima River in Washington
This specimen appears to be of the same species as this one collected in the same spot two months earlier. The identification of both is tentative. This one suffered some physical damage before being photographed, too, so the colors aren't totally natural. I was mostly photographing it to test out some new camera setting idea, which worked really well for a couple of closeups.
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 Heptagenia dolosa

Where & when

In 3 records from GBIF, adults of this species have been collected during June (67%) and August (33%).

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: 8 mm
Wing length: 8 mm

A pale species closely allied to Heptagenia marginalis; genitalia of the Heptagenia flavescens type.

Head pale yellowish white; frontal shelf hyaline, anterior margin narrowly purplish black; a faint line of same color on each side of carina below antenna. Base of antenna white; filament faintly dusky at base, tip pale. Four small inconspicuous spots on vertex; two on posterior margin, two anterior to these, one near each ocellus. Eyes very large, blue-black in alcohol. Thorax pale yellowish white. Lateral margin and an oblique lateral stripe on pronotum black; a black streak above fore coxa. Two large and one small black spots above middle coxa, arranged as in H. marginalis; a small black dot above and behind hind coxa, similar dark dot on lateral margin of metanotum. Mesonotum unmarked. Legs pale whitish; extreme base of fore femur reddish brown; a narrow apical streak, a wide median band, and a streak along the ventral edge, deep purplish red. Apex of fore tibia, and distal tarsal joint, narrowly brown; basal tarsal joint with faint brown shading. Middle and hind femora pale basally, median bands pale and incomplete; apical streak often incomplete, apices of tibiae and tarsal claws purplish. Three main veins of costal margin heavy, yellowish; other veins fine, brownish: 4 to 5 costal crossveins before bulla, 12 to 15 beyond it.

Abdominal segments 1-8 white, hyaline; 9 and 10 opaque, creamy yellow. Posterior margin of each tergite narrowly purplish black; a blackish longitudinal streak on each side of each tergite, halfway between median line and pleural fold; a faint oblique dark mark at each spiracle; tergites 6 and 7, occasionally also 9 and 10, with traces of a faint dark mid-dorsal streak. Dark markings less prominent than in H. marginalis. Genitalia creamy white. Details of structure of penes differ somewhat from marginalis (see fig. 95). Second forceps joint somewhat shorter relatively than in that species. Tails wholly whitish.

The smaller size, paler color of tail, single median femoral band, lack of dark mesonotal markings and more restricted mid-dorsal markings on tergites, as well as details in the structure of the penes, distinguish this species from marginalis.


Start a Discussion of Heptagenia dolosa

References

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

Mayfly Species Heptagenia dolosa

Species Range
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