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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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Female Ephemerella invaria (Sulphur) Mayfly Dun Pictures

This mayfly was collected from unknown in Wisconsin on May 23rd, 2004 and added to Troutnut.com by Troutnut on January 25th, 2006.

Discussions of this Dun

Another sulphur for comment
1 replies
Posted by Martinlf on Aug 17, 2007
Last reply on Aug 21, 2007 by Gene
And this one, also from the midwest, is more green than the sulphurs I recall seeing this season. My limited experience in PA streams suggests that many, if not most, of the sulphurs here are best imitated by pale yellow, bright yellow, or orange bodies. Gene, and others, am I far off?

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References

Female Ephemerella invaria (Sulphur) Mayfly Dun Pictures

Collection details
Location: unknown, Wisconsin
Date: May 23rd, 2004
Added to site: January 25th, 2006
Author: Troutnut
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