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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.

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 Siphlonurus rapidus (Gray Drakes)

This species may reinforce spinner flights of Siphlonurus quebecensis and Siphlonurus alternatus.

Where & when

Time of year : May through June

Most accounts say this species hatches through June, but Knopp and Cormier in Mayflies: An Angler's Study of Trout Water Ephemeroptera say it may last through the end of September.

In 29 records from GBIF, adults of this species have mostly been collected during June (72%), July (14%), and May (10%).

In 1 record from GBIF, this species has been collected at elevation of 1401 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

Body length: 10 mm
Wing length: 12 mm

A medium-sized light brown species, having a discontinuous mid-ventral brown stripe.

Head grey to yellowish. Thorax dull yellowish to olive brown. Mesonotum yellowish, shaded with reddish brown on the median area. A pale spot before the scutellum. Scutellum reddish brown. Purplish streak anterior to wing roots. Pleural sutures yellowish. Pale bands across the mesosterna and metasterna. Fore leg yellowish brown, the tarsi yellowish; joinings purplish brown. Middle and hind legs yellowish, the femora washed with purplish brown; joinings purplish brown. Wings hyaline, very faintly tinged with brown. Stigmatic area opaque whitish. Veins dark purplish brown. All costal cross veins distinct, brown; about 11 before the bulla, 21-23 beyond it, in the stigmatic area. The latter veins are occasionally forked and anastomosed near the costal margin.

Abdomen purplish brown dorsally. The usual dark lateral triangles present, more or less diffuse; dark oval spots small, indistinct. Pale anterior triangles semi-hyaline, whitish; much reduced in size on the basal and apical tergites. Ventrally pale yellowish white, with a discontinuous dark purplish brown mid-ventral streak. Sternites 1 and 2 largely purplish brown. Forceps base yellowish white, forceps and penes brown. Tails yellowish white, joinings purplish brown. Genitalia as in fig. 122.

Start a Discussion of Siphlonurus rapidus


Mayfly Species Siphlonurus rapidus (Gray Drakes)

Species Range
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