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.

Middle Fork Snoqualmie

From the Middle Fork Snoqualmie River in Washington

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.

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Mayfly Species Ephemerella unicornis

Physical description

Most physical descriptions on Troutnut are direct or slightly edited quotes from the original scientific sources describing or updating the species, although there may be errors in copying them to this website. Such descriptions aren't always definitive, because species often turn out to be more variable than the original describers observed. In some cases, only a single specimen was described! However, they are useful starting points.

Male Spinner

Described in Needham et al (1935)

Body length: 5 mm
Wing length: 5 mm

The identity of this species, defined from a single male subimago, cannot at the present time be correctly determined. The character by which this species was distinguished, “an erect conic tubercle upon the front margin of the middle lobe of the mesothorax,” is said by Dr. McDunnough to “occur sporadically in several species very similar in the subimago stage.”

Start a Discussion of Ephemerella unicornis

References

Needham, James G., Jay R. Traver, and Yin-Chi Hsu. 1935. The Biology of Mayflies. Comstock Publishing Company, Inc.