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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 Holocentropus (Polycentropodidae) Caddisfly Larva from the Yakima River in Washington
This one seems to tentatively key to Holocentropus, although I can't make out the anal spines in Couplet 7 of the Key to Genera of Polycentropodidae Larvae nor the dark bands in Couplet 4 of the Key to Genera of Polycentropodidae Larvae, making me wonder if I went wrong somewhere in keying it out. I don't see where that could have happened, though. It might also be that it's a very immature larva and doesn't possess all the identifying characteristics in the key yet. If Holocentropus is correct, then Holocentropus flavus and Holocentropus interruptus are the two likely possibilities based on range, but I was not able to find a description of their larvae.
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 Acerpenna pygmaea (Tiny Blue-Winged Olive) Mayfly Spinner Pictures

Ventral view of a Female Acerpenna pygmaea (Baetidae) (Tiny Blue-Winged Olive) Mayfly Spinner from the Henry's Fork of the Snake River in Idaho
Lateral view of a Female Acerpenna pygmaea (Baetidae) (Tiny Blue-Winged Olive) Mayfly Spinner from the Henry's Fork of the Snake River in Idaho
Female Acerpenna pygmaea (Baetidae) (Tiny Blue-Winged Olive) Mayfly Spinner from the Henry's Fork of the Snake River in Idaho
Female Acerpenna pygmaea (Baetidae) (Tiny Blue-Winged Olive) Mayfly Spinner from the Henry's Fork of the Snake River in Idaho
Dorsal view of a Female Acerpenna pygmaea (Baetidae) (Tiny Blue-Winged Olive) Mayfly Spinner from the Henry's Fork of the Snake River in Idaho
Ruler view of a Female Acerpenna pygmaea (Baetidae) (Tiny Blue-Winged Olive) Mayfly Spinner from the Henry's Fork of the Snake River in Idaho The smallest ruler marks are 1 mm.

This mayfly was collected from the Henry's Fork of the Snake River in Idaho on July 31st, 2020 and added to Troutnut.com by Troutnut on August 17th, 2020.


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Female Acerpenna pygmaea (Tiny Blue-Winged Olive) Mayfly Spinner Pictures

Collection details
Location: Henry's Fork of the Snake River, Idaho
Date: July 31st, 2020
Added to site: August 17th, 2020
Author: Troutnut
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