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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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Male Ephemerella excrucians (Pale Morning Dun) Mayfly Nymph Pictures

I used the ID of this nymph (and some others like it) to infer the identity of a female dun collected on the same trip.

This specimen (top left) is pictured with a couple others from the same kicknet sample just to show the variation in color.

Male Ephemerella excrucians (Ephemerellidae) (Pale Morning Dun) Mayfly Nymph from Mystery Creek #249 in Washington
Male Ephemerella excrucians (Ephemerellidae) (Pale Morning Dun) Mayfly Nymph from Mystery Creek #249 in Washington
Male Ephemerella excrucians (Ephemerellidae) (Pale Morning Dun) Mayfly Nymph from Mystery Creek #249 in Washington
Male Ephemerella excrucians (Ephemerellidae) (Pale Morning Dun) Mayfly Nymph from Mystery Creek #249 in Washington
Male Ephemerella excrucians (Ephemerellidae) (Pale Morning Dun) Mayfly Nymph from Mystery Creek #249 in Washington
Dorsal view of a Male Ephemerella excrucians (Ephemerellidae) (Pale Morning Dun) Mayfly Nymph from Mystery Creek #249 in Washington
Lateral view of a Male Ephemerella excrucians (Ephemerellidae) (Pale Morning Dun) Mayfly Nymph from Mystery Creek #249 in Washington
Ruler view of a Male Ephemerella excrucians (Ephemerellidae) (Pale Morning Dun) Mayfly Nymph from Mystery Creek #249 in Washington The smallest ruler marks are 1 mm.
Male Ephemerella excrucians (Ephemerellidae) (Pale Morning Dun) Mayfly Nymph from Mystery Creek #249 in Washington
Male Ephemerella excrucians (Ephemerellidae) (Pale Morning Dun) Mayfly Nymph from Mystery Creek #249 in Washington
Ventral view of a Male Ephemerella excrucians (Ephemerellidae) (Pale Morning Dun) Mayfly Nymph from Mystery Creek #249 in Washington

This mayfly was collected from Mystery Creek #249 in Washington on July 4th, 2020 and added to Troutnut.com by Troutnut on July 12th, 2020.


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Male Ephemerella excrucians (Pale Morning Dun) Mayfly Nymph Pictures

Collection details
Location: Mystery Creek #249, Washington
Date: July 4th, 2020
Added to site: July 12th, 2020
Author: Troutnut
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