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.

Stream photos

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Limnephilidae (Giant Sedges) Caddisfly Larva Limnephilidae (Giant Sedges) Caddisfly Larva

Dorsal view of a Limnephilidae (Giant Sedges) Caddisfly Larva from the Yakima River in Washington

This specimen resembled several others of around the same size and perhaps the same species, which were pretty common in my February sample from the upper Yakima. Unfortunately, I misplaced the specimen before I could get it under a microscope for a definitive ID.

10 Recently Added Photos

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.

Troutnut is a project started in 2003 by salmonid ecologist Jason "Troutnut" Neuswanger to help anglers and fly tyers unabashedly embrace the entomological side of the sport. Learn more about Troutnut or support the project for an enhanced experience here.

Medium Olive Duns

This common name refers to only one species. Click its scientific name to learn more.

Mayfly Species Acerpenna pygmaea

These are very rarely called Medium Olive Duns.

This species is known in older taxonomies under the former name Baetis pygmaeus.
It is a diminutive baetid with distribution across every region. It is reported to have localized hatches of occasional importance.

Male Acerpenna pygmaea (Tiny Blue-Winged Olive) Mayfly Spinner

8 Pictures

Lateral view of a Male Acerpenna pygmaea (Baetidae) (Tiny Blue-Winged Olive) Mayfly Spinner from the Henry's Fork of the Snake River in Idaho

Collected July 31, 2020 from the Henry's Fork of the Snake River in Idaho

Added by Troutnut on August 17, 2020

Collected July 31, 2020 from the Henry's Fork of the Snake River in Idaho and added by Troutnut on August 17, 2020

Acerpenna pygmaea (Tiny Blue-Winged Olive) Mayfly Nymph

3 Pictures

Acerpenna pygmaea (Baetidae) (Tiny Blue-Winged Olive) Mayfly Nymph from the Upper Stillwater River in Montana

This is a very rare mayfly in western Montana. The shape of the last gill is a key to its identification. I have collected this species in only one location.

Collected May 4, 2007 from the Upper Stillwater River in Montana

Added by Bnewell on June 26, 2011

Collected May 4, 2007 from the Upper Stillwater River in Montana and added by Bnewell on June 26, 2011

See 3 more specimens...