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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 Baetisca laurentina (Armored Mayfly) Mayfly Dun Pictures

Lateral view of a Female Baetisca laurentina (Baetiscidae) (Armored Mayfly) Mayfly Dun from the Marengo River in Wisconsin
Female Baetisca laurentina (Baetiscidae) (Armored Mayfly) Mayfly Dun from the Marengo River in Wisconsin
Ventral view of a Female Baetisca laurentina (Baetiscidae) (Armored Mayfly) Mayfly Dun from the Marengo River in Wisconsin
Artistic view of a Female Baetisca laurentina (Baetiscidae) (Armored Mayfly) Mayfly Dun from the Marengo River in Wisconsin
Female Baetisca laurentina (Baetiscidae) (Armored Mayfly) Mayfly Dun from the Marengo River in Wisconsin
Female Baetisca laurentina (Baetiscidae) (Armored Mayfly) Mayfly Dun from the Marengo River in Wisconsin
Female Baetisca laurentina (Baetiscidae) (Armored Mayfly) Mayfly Dun from the Marengo River in Wisconsin

This mayfly was collected from the Marengo River in Wisconsin on June 5th, 2005 and added to Troutnut.com by Troutnut on May 25th, 2006.

Discussions of this Dun

Wow
1 replies
Posted by Taxon on Jun 26, 2006
Last reply on Jun 26, 2006 by Troutnut
Jason-

Wow, believe these are the first photos I've seen of winged Baetisca. They certainly have a stout abdomen, don't they. Guess that shouldn't be a particular surprise given the shape of the nymphs, but must admit it startled me.

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References

Female Baetisca laurentina (Armored Mayfly) Mayfly Dun Pictures

Collection details
Location: Marengo River, Wisconsin
Date: June 5th, 2005
Added to site: May 25th, 2006
Author: Troutnut
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