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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.

Lateral view of a Female Sweltsa borealis (Chloroperlidae) (Boreal Sallfly) Stonefly Adult from Harris Creek in Washington
I was not fishing, but happened to be at an unrelated social event on a hill above this tiny creek (which I never even saw) when this stonefly flew by me. I assume it came from there. Some key characteristics are tricky to follow, but process of elimination ultimately led me to Sweltsa borealis. It is reassuringly similar to this specimen posted by Bob Newell years ago. It is also so strikingly similar to this nymph from the same river system that I'm comfortable identifying that nymph from this adult. I was especially pleased with the closeup photo of four mites parasitizing this one.
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 Epeorus deceptivus Mayfly Dun Pictures

The lack of a darkened humeral crossvein rules out Epeorus albertae and Epeorus dulciana. The lack of a dark macula on the forefemora rules out Epeorus longimanus. The small size rules out Epeorus grandis and Epeorus permagnus. That leaves as the only possibility known in Washington state Epeorus deceptivus. It is a small species, although not reportedly quite as small as this specimen. I couldn't find anything in the species description in Traver (1935) to definitively confirm or rule out the species ID, given that I don't have the preserved specimen to check under a microscope, but it has to be either deceptivus or something not yet reported in Washington.

It was collected at the same time as a similar-sized female dun.

Male Epeorus deceptivus (Heptageniidae) Mayfly Dun from the South Fork Sauk River in Washington
Male Epeorus deceptivus (Heptageniidae) Mayfly Dun from the South Fork Sauk River in Washington
Male Epeorus deceptivus (Heptageniidae) Mayfly Dun from the South Fork Sauk River in Washington
Male Epeorus deceptivus (Heptageniidae) Mayfly Dun from the South Fork Sauk River in Washington
Lateral view of a Male Epeorus deceptivus (Heptageniidae) Mayfly Dun from the South Fork Sauk River in Washington
Male Epeorus deceptivus (Heptageniidae) Mayfly Dun from the South Fork Sauk River in Washington
Ventral view of a Male Epeorus deceptivus (Heptageniidae) Mayfly Dun from the South Fork Sauk River in Washington
Male Epeorus deceptivus (Heptageniidae) Mayfly Dun from the South Fork Sauk River in Washington
Tick marks are 1/16"

Ruler view of a Male Epeorus deceptivus (Heptageniidae) Mayfly Dun from the South Fork Sauk River in Washington The smallest ruler marks are 1/8".
Male Epeorus deceptivus (Heptageniidae) Mayfly Dun from the South Fork Sauk River in Washington
Artistic view of a Male Epeorus deceptivus (Heptageniidae) Mayfly Dun from the South Fork Sauk River in Washington
Male Epeorus deceptivus (Heptageniidae) Mayfly Dun from the South Fork Sauk River in Washington

This mayfly was collected from the South Fork Sauk River in Washington on July 5th, 2017 and added to Troutnut.com by Troutnut on July 6th, 2017.

Discussions of this Dun

ID on this one?
Posted by Troutnut on Jul 6, 2017
Last reply on Jul 6, 2017 by Troutnut
See the caption for the specimen -- I'm thinking Epeorus dulciana based on size and geographic distribution alone, but I can't find any information about how their duns look. Pretty mayfly, though!

Start a Discussion of Dun

Male Epeorus deceptivus Mayfly Dun Pictures

Collection details
Location: South Fork Sauk River, Washington
Date: July 5th, 2017
Added to site: July 6th, 2017
Author: Troutnut
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