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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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Dark Blue-Winged Olives

Like most common names,"Dark Blue-Winged Olive" can refer to more than one taxon. They're previewed below, along with 2 specimens. For more detail click through to the scientific names.

Mayfly Species Baetis flavistriga

These are often called Dark Blue-Winged Olives.
This is one of the most widespread and abundant Baetis species, and it may produce fishable hatches under a variety of conditions.

This species is known in angling books by several old synonyms, including Baetis quebecensus, Baetis levitans, Baetis cingulatus, and Baetis phoebus, in addition to the correct name.
Dorsal view of a Male Baetis flavistriga (Baetidae) (BWO) Mayfly Nymph from the Dosewallips River in Washington
This nymph keys to Baetis assuming the villipore is present (hard to see in my photos or scope), and within that genus it tentatively keys to the flavistriga species complex, of which Baetis flavistriga itself is by far the most common in Washington state, so that's the most likely ID.

Mayfly Species Attenella attenuata

These are very rarely called Dark Blue-Winged Olives.
This intriguing species has received a lot of attention in past angling books. Recent authors suspect that much of this credit was a case of mistaken identity, with Attenella attenuata receiving praise for the hatches of Drunella lata and Dannella simplex. Much of the credit was legitimate and accurate, but this species is no longer thought to be on par with its most popular cousins in Ephemerella and Drunella.

I have several specimens listed under this species, but I'm not positive the identification is correct.
Lateral view of a Female Attenella attenuata (Ephemerellidae) (Blue-Winged Olive) Mayfly Dun from the Namekagon River in Wisconsin
This specimen came from the same hatch as a male.

References

Dark Blue-Winged Olives

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