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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 Ephemerella mucronata (Ephemerellidae) Mayfly Nymph from the Yakima River in Washington
This is an interesting one. Following the keys in Merritt R.W., Cummins, K.W., and Berg, M.B. (2019) and Jacobus et al. (2014), it keys clearly to Ephemerella. Jacobus et al provide a key to species, but some of the characteristics are tricky to interpret without illustrations. If I didn't make any mistakes, this one keys to Ephemerella mucronata, which has not previously been reported any closer to here than Montana and Alberta. The main character seems to fit well: "Abdominal terga with prominent, paired, subparallel, spiculate ridges." Several illustrations or descriptions of this holarctic species from the US and Europe seem to match, including the body length, tarsal claws and denticles, labial palp, and gill shapes. These sources include including Richard Allen's original description of this species in North America under the now-defunct name E. moffatae in Allen RK (1977) and the figures in this description of the species in Italy.
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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Dorsal view of a Pteronarcys dorsata (Pteronarcyidae) (Salmonfly) Stonefly Nymph from the Namekagon River in Wisconsin
Adirman
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Monticello, NY

Posts: 479
Adirman on Sep 10, 2010September 10th, 2010, 11:06 pm EDT
Hey, what'sm with those wierd fuzzy looking things under its belly and forearms? Is that some sort of traction thing for sticking to stuff?
Taxon
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Site Editor
Plano, TX

Posts: 1311
Taxon on Sep 11, 2010September 11th, 2010, 3:55 am EDT
Adirman-

Interesting guess, but those are called gills, and are used to "breathe" dissolved oxygen from the water. Stonefly family generally determines whether or not gills are possessed, where they are located on the body, and the form they take, finger-like or filamentous, simple or branched, etc.
Best regards,
Roger Rohrbeck
www.FlyfishingEntomology.com
Adirman
Adirman's profile picture
Monticello, NY

Posts: 479
Adirman on Sep 11, 2010September 11th, 2010, 5:56 am EDT
Taxon;

Thanks for the info!!

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