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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 Zapada cinctipes (Nemouridae) (Tiny Winter Black) Stonefly Nymph from the Yakima River in Washington
Nymphs of this species were fairly common in late-winter kick net samples from the upper Yakima River. Although I could not find a key to species of Zapada nymphs, a revision of the Nemouridae family by Baumann (1975) includes the following helpful sentence: "2 cervical gills on each side of midline, 1 arising inside and 1 outside of lateral cervical sclerites, usually single and elongate, sometimes constricted but with 3 or 4 branches arising beyond gill base in Zapada cinctipes." This specimen clearly has the branches and is within the range of that species.
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 Genus Acerpenna (Tiny Blue-Winged Olives)

See Acerpenna pygmaea for details. It is the only species known to be of even minor importance to anglers and was previously known as Baetis pygmaeus.

Where & when

In 38 records from GBIF, adults of this genus have been collected during July (37%), June (26%), May (18%), April (8%), September (5%), and August (5%).

In 52 records from GBIF, this genus has been collected at elevations ranging from 3 to 4692 ft, with an average (median) of 1713 ft.

Genus Range

Specimens of the Mayfly Genus Acerpenna

2 Male Spinners
2 Female Spinners
1 Nymph

Start a Discussion of Acerpenna


Mayfly Genus Acerpenna (Tiny Blue-Winged Olives)

3 species (Acerpenna macdunnoughi, Acerpenna sulfurosa, and Acerpenna thermophilos) aren't included.
Genus Range
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