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.

The Clark's Fork of the Yellowstone River in Wyoming

Stream photos

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Perlodidae (Springflies and Yellow Stones) Stonefly Nymph Perlodidae (Springflies and Yellow Stones) Stonefly Nymph

Artistic view of a Perlodidae (Springflies and Yellow Stones) Stonefly Nymph from the Yakima River in Washington

This one seems to lead to Couplet 35 of the Key to Genera of Perlodidae Nymphs and the genus Isoperla, but I'm skeptical that's correct based on the general look. I need to get it under the microscope to review several choices in the key, and it'll probably end up a different Perlodidae.

11 Recently Added Photos

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 Metretopus borealis (Pseudo-Gray Drakes)

Where & when

In 32 records from GBIF, adults of this species have mostly been collected during July (38%), August (28%), June (25%), and September (6%).

In 279 records from GBIF, this species has been collected at elevations ranging from -30 to 3524 ft, with an average (median) of 919 ft.

Species Range

source

Map of specific collection sites

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 Metretopus norvegicus

Body length: 10 mm
Wing length: 9 mm

A brownish species, the middle abdominal segments of the male translucent; only species of the genus known in North America.

Thorax pitch-black above. Body somewhat discolored. Abdominal segment 1, and segments 7-10, bistre brown; the middle segments translucent. Posterior margins of tergites narrowly marked with umber brown. Mid-dorsal line of the same color, also “an oblique linear lanceolate streak on each side produced forwards from it, so as to constitute a tridentate marking, enclosing on each side of the dorsum a large almost right-angled triangular translucent space, rounded at the posterior angle, the shortest side of which is at the base of the segment. From the right angle of this triangle a fine tapering blackish streak proceeds towards the middle of the hypotenuse” (Eaton). Tails uniformly dark grey. The apical margin of the ninth sternite of the female is entire, and convex. The penes are divided half way to the base; each free portion is rather linear, and directed slightly outward, having a rounded lobe on the inner apical margin (see fig. 114).