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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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Feathers5
Posts: 287
Feathers5 on Aug 20, 2014August 20th, 2014, 7:35 am EDT
Can someone direct me to some links to the Fall BWOs that hatch in the East? Usually, we see them from September to November and they are very small, size 18 to 24 or maybe even 26s. I've looked and I can't figure it out.
Thanks for your help,
Bruce
Baetis7
MI

Posts: 17
Baetis7 on Aug 20, 2014August 20th, 2014, 9:19 am EDT
Try the hatch chart at Trailstotrout.com I believe they mention the Genus and species and sizes. As far as pics and patterns you may want to try Dick Pobst's Trout Stream Insect book which is a great pocket guide book for Eastern insect hatches. Best of action out there!
Entoman
Entoman's profile picture
Northern CA & ID

Posts: 2604
Entoman on Aug 20, 2014August 20th, 2014, 11:08 am EDT
Hey Bruce,

Check out the commentaries in the encyclopedia. I believe them to be the most concise explanations on the web (for anglers) as to where we stand currently with this most confusing family. Under the genus Baetis is a list of the names used in older angling texts that is a great help in making them relevant and easier to enterpret.

Bottom line though is that there is still no substitute for capturing your own specimens for matching both size and color. The same species can vary quite a bit in both characters depending on location. They all have pretty much the same behavior, so a good match should fish just as well (or bad) whether you're right about the species or not.
"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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