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.

Of all the pools I've fished, this one was most deserving of the colorful little brook trout it held.

From Mystery Creek # 89 in New York

Stream photos

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Male Baetidae (Blue-Winged Olive) Mayfly Dun Male Baetidae (Blue-Winged Olive) Mayfly Dun

Lateral view of a Male Baetidae (Blue-Winged Olive) Mayfly Dun from Mystery Creek #308 in Washington

This dun emerged from a mature nymph on my desk. Unfortunately its wings didn't perfectly dry out.

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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 Acerpenna akataleptos

Species Range

source

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 Baetis akataleptos

Body length: 2.5 mm
Wing length: 3 mm

Abdominal tergites 2-6 of male dull brown; genitalia of the Baetis intercalaris type ; hind wing two-veined, costal projection prominent.

Turbinate eyes of male imago small, oval in shape, and dark reddish brown. Thorax blackish brown. Legs pale smoky, the tarsi whitish. Wings hyaline, venation pale; cross veins in the stigmatic area of the fore wing few in number, not well developed, and without granulations. No intercalaries in the first interspace. Hind wing long and narrow; only two veins, the third one entirely lacking; costal projection prominent.

Abdominal tergites 2-6 semi-translucent, dull brown, sternites similar; posterior segments opaque, brighter brown. Genitalia very similar to B. pygmaeus (now a synonym of Acerpenna pygmaea), but with a finely setose projecting penis-cover, which is not present in that species, between the bases of the forceps. Related also to B. harti (now a synonym of Acerpenna pygmaea). Distinguishable from these species by reason of the brown basal segments of the abdomen.

Start a Discussion of Acerpenna akataleptos

References

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