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Lateral view of a Male Baetis (Baetidae) (Blue-Winged Olive) Mayfly Dun from Mystery Creek #43 in New York
Blue-winged Olives
Baetis

Tiny Baetis mayflies are perhaps the most commonly encountered and imitated by anglers on all American trout streams due to their great abundance, widespread distribution, and trout-friendly emergence habits.

Dorsal view of a Setvena wahkeena (Perlodidae) (Wahkeena Springfly) Stonefly Nymph from Mystery Creek #199 in Washington
As far as I can tell, this species has only previously been reported from one site in Oregon along the Columbia gorge. However, the key characteristics are fairly unmistakable in all except for one minor detail:
— 4 small yellow spots on frons visible in photos
— Narrow occipital spinule row curves forward (but doesn’t quite meet on stem of ecdysial suture, as it's supposed to in this species)
— Short spinules on anterior margin of front legs
— Short rposterior row of blunt spinules on abdominal tergae, rather than elongated spinules dorsally
I caught several of these mature nymphs in the fishless, tiny headwaters of a creek high in the Wenatchee Mountains.
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 excrucians (Pale Morning Dun) Mayfly Dun Pictures

Although there is no key to female duns, I'm calling this dun Ephemerella excrucians because I collected several mature nymphs of that species on the same trip.

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

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