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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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This topic is about the Mayfly Genus Tricorythodes

A cult following is something to which few insects can lay claim, but the tiny Tricorythodes mayflies certainly qualify. Their widespread, reliable, heavy hatches draw impressive rises of ultra-selective trout which demand the most of a technical dry-fly angler's skills.

It is surprising that such a great hatch took so long to come to the attention of fly fishermen. The Tricos were first introduced to anglers in a 1969 Outdoor Life article by Vincent Marinaro, who misidentified them as Caenis. By the early 1970s the identification had been corrected but Swisher and Richards still wrote in Selective Trout, "Few anglers are familiar with these extremely small but important mayflies." The next wave of publications boosted Tricorythodes to its current fame. I suspect their early dismissal was due in part to tackle limitations; anglers in the 1950s had no means to effectively tie and present size 22-28 flies.

Example specimens

Lastchance
Portage, PA

Posts: 437
Lastchance on Jul 2, 2011July 2nd, 2011, 2:40 pm EDT
Do they attach themselves in the silt near the shore? I'd like to study a few of them.
Thanks,
Bruce
Konchu
Konchu's profile picture
Site Editor
Indiana

Posts: 498
Konchu on Jul 2, 2011July 2nd, 2011, 4:25 pm EDT
I have found them among rocks where there's some flow in the stream, but theres often a fair amount of silt in with them. Doesn't mean they're not where you suggested--just my experience.
Spinnerfall
Spinnerfall's profile picture
Boulder, CO

Posts: 3
Spinnerfall on Jul 9, 2011July 9th, 2011, 9:38 pm EDT
Informative. Thanks Konchu!
Entoman
Entoman's profile picture
Northern CA & ID

Posts: 2604
Entoman on Jul 10, 2011July 10th, 2011, 9:41 am EDT
Hi Tim,

I've also found them at the bases of rooted weeds in the silt, and in the weeds themselves as they stage for hatching.

Regards,

Kurt

"It's not that I find fishing so important, it's just that I find all other endeavors of Man equally unimportant... And not nearly as much fun!" Robert Traver, Anatomy of a Fisherman

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