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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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TimCat
TimCat's profile picture
Alanson, MI

Posts: 121
TimCat on May 1, 2016May 1st, 2016, 5:58 pm EDT
I fished the Black River in Michigan about a half hour from gaylord this Saturday morning. The only bugs I "recognized" on the surface were some sporadic Blue-Winged Olives coming off the surface. Not much of a hatch in the classic sense, and no fish were rising either. The water was just above 40 degrees F. As a novice, I am not positive this was baetis or baetidae, but they were green mayflies with purpleish and pinkish wings. These guys were tiny. If I had to guess a hook size for them it would be 24-26 or smaller. Is this possible for BWOs or am I mistaken? I always thought they weren't much smaller than size 18.

Sorry I don't have any pictures, but even if I took the time to take one, my phone would not be able to focus on something that small.
"If I'm not going to catch anything, then I 'd rather not catch anything on flies" - Bob Lawless
Entoman
Entoman's profile picture
Northern CA & ID

Posts: 2604
Entoman on May 1, 2016May 1st, 2016, 6:27 pm EDT
No, you are probably right about them being baetids, though the odds are they probably aren't in the genus Baetis. The wing color you noticed sounds like a description of spinner wings in the right light conditions.
"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
TimCat
TimCat's profile picture
Alanson, MI

Posts: 121
TimCat on May 2, 2016May 2nd, 2016, 3:27 pm EDT
Gotcha. Thanks for the reply. I was just surprised to see them being so small. I had nothing in my box even remotely close to that size, not even trico patterns.
"If I'm not going to catch anything, then I 'd rather not catch anything on flies" - Bob Lawless

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