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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 Leucrocuta hebe (Heptageniidae) (Little Yellow Quill) Mayfly Nymph from the Bois Brule River in Wisconsin
GONZO
Site Editor
"Bear Swamp," PA

Posts: 1681
GONZO on Jul 19, 2011July 19th, 2011, 4:10 am EDT
This looks more like a Leucrocuta nymph to me (possibly L. hebe?).
Troutnut
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Administrator
Bellevue, WA

Posts: 2758
Troutnut on Jul 19, 2011July 19th, 2011, 9:37 am EDT
Thanks, you're right on the genus for sure. There's no fibrilliform portion on gill 7, and the tails only have spines at the segments. I'd guess you're right on the species too but I don't know.
Jason Neuswanger, Ph.D.
Troutnut and salmonid ecologist
GONZO
Site Editor
"Bear Swamp," PA

Posts: 1681
GONZO on Jul 19, 2011July 19th, 2011, 4:24 pm EDT
It's difficult to be certain of the species, Jason. If reliable keys to the nymphs exist, I haven't seen them, and McCafferty (2004) says that some of the species are "questionably valid."

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