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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.

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.
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 Cinygmula mimus

Where & when

In Mayflies: An Angler's Study of Trout Water Ephemeroptera , Knopp and Cormier report "occasional" fishable hatches of this species from southern Alberta, and its known range extends down the east slope of the Rockies into the United States.

In 11 records from GBIF, adults of this species have been collected during July (36%), May (27%), June (18%), August (9%), and September (9%).

In 14 records from GBIF, this species has been collected at elevations ranging from 3202 to 9285 ft, with an average (median) of 7156 ft.

Species Range

Hatching behavior

Time of day : Late July through early September

Nymph biology

Environmental tolerance: Prefers cool water

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 mm
Wing length: 10 mm

A rather large species, the wings tinged with yellowish brown; spine on inner margin of each side of penes only.

Head reddish to purplish brown. Thoracic notum light chestnut brown; remainder of thorax yellowish brown with reddish tinges; paler yellowish or creamy areas anterior to wing root, and below bases of wings on pleura. Legs light yellowish brown; tibia-tarsal joint and tarsal joinings of fore leg darker brown; claws of all legs brownish; tarsal joinings of middle and hind legs narrowly brown, distal tarsal joints tinged with light brown. Wings hyaline, the membrane tinged with yellowish brown, especially evident in hind wing and basal half of fore wing. Venation light yellowish brown, the cross veins often faintly red-brown. Abdominal segments 2-7 semi-hyaline, pale purplish to light madder brown; extreme anterior margin colorless, posterior margins narrowly darker. Sternites very similar to tergites, but somewhat paler; no dark mid-ventral markings. Segments 8-10 opaque, yellowish brown with a tinge of purple or madder; sternites more yellowish than tergites. Tails yellowish brown, often with faint red-brown tinge in basal portion; joinings opaque, faintly darker. Forceps light red-brown, penes yellow-brown; penes divergent almost from base, bearing on each side a single spine on inner margin. (See fig. 103, gartrelli).

The yellowish brown tinge of the wings, the absence of dark ventral markings and the details of structure of the penes, when taken together, distinguish this from other allied species.

Specimens of the Mayfly Species Cinygmula mimus

2 Male Spinners
1 Female Spinner

Start a Discussion of Cinygmula mimus


Mayfly Species Cinygmula mimus

Species Range
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