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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 Zapada cinctipes (Nemouridae) (Tiny Winter Black) Stonefly Nymph from the Yakima River in Washington
Nymphs of this species were fairly common in late-winter kick net samples from the upper Yakima River. Although I could not find a key to species of Zapada nymphs, a revision of the Nemouridae family by Baumann (1975) includes the following helpful sentence: "2 cervical gills on each side of midline, 1 arising inside and 1 outside of lateral cervical sclerites, usually single and elongate, sometimes constricted but with 3 or 4 branches arising beyond gill base in Zapada cinctipes." This specimen clearly has the branches and is within the range of that species.
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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Epeorus longimanus (Slate Brown Dun) Mayfly Nymph Pictures

Dorsal view of a Epeorus longimanus (Heptageniidae) (Slate Brown Dun) Mayfly Nymph from Mystery Creek #249 in Washington
Although difficult to tell in this picture, the gills on the first abdominal segment do meet ventrally in this specimen, a key characteristic for identification.

Ventral view of a Epeorus longimanus (Heptageniidae) (Slate Brown Dun) Mayfly Nymph from Mystery Creek #249 in Washington
Ruler view of a Epeorus longimanus (Heptageniidae) (Slate Brown Dun) Mayfly Nymph from Mystery Creek #249 in Washington The smallest ruler marks are 1 mm.
Epeorus longimanus (Heptageniidae) (Slate Brown Dun) Mayfly Nymph from Mystery Creek #249 in Washington
Epeorus longimanus (Heptageniidae) (Slate Brown Dun) Mayfly Nymph from Mystery Creek #249 in Washington
Epeorus longimanus (Heptageniidae) (Slate Brown Dun) Mayfly Nymph from Mystery Creek #249 in Washington
Epeorus longimanus (Heptageniidae) (Slate Brown Dun) Mayfly Nymph from Mystery Creek #249 in Washington
Here the meeting and slight overlap on the first pair of gills is more evident.

Epeorus longimanus (Heptageniidae) (Slate Brown Dun) Mayfly Nymph from Mystery Creek #249 in Washington
Epeorus longimanus (Heptageniidae) (Slate Brown 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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Epeorus longimanus (Slate Brown 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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