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.

Upper Titcomb Lake

From Titcomb Basin in Wyoming

Stream photos

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Sweltsa (Sallfly) Stonefly Nymph Sweltsa (Sallfly) Stonefly Nymph

Dorsal view of a Sweltsa (Chloroperlidae) (Sallfly) Stonefly Nymph from the Yakima River in Washington

This species was fairly abundant in a February sample of the upper Yakima.

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 Procloeon pennulatum (Tiny Sulphur Duns)

Where & when

In 16 records from GBIF, adults of this species have been collected during July (44%), October (25%), September (13%), June (13%), and August (6%).

In 74 records from GBIF, this species has been collected at elevations ranging from 3 to 4183 ft, with an average (median) of 1467 ft.

Species Range

source

Map of specific collection sites

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.

Female Spinner

Described in Needham et al (1935) as Centroptilum infrequens

Body length: 7 mm
Wing length: 8 mm

A large species, of which only the female imago is known; distinctive by reason of the prominent ruddy dorsal stripe and large size.

Thorax of female light ochreous, shaded with creamy. Legs pale yellow. Wings hyaline, venation pale. Hind wing long and very narrow; two longitudinal veins, united for a short distance at the base, then running close to each other to beyond the costal projection, which is long and hook-like. Abdomen pale yellowish; last three segments opaque, others semi-hyaline. A broad and prominent ruddy stripe extends the entire length of the abdomen dorsally, deepest in color on tergites 7-9, and containing two pairs of minute hyaline submedian dots.

This species is apparently related to C. quaesitum (now a synonym of Procloeon quaesitum), but the female of that species has a pale yellowish abdomen, the posterior margins of the tergites tinged with brown.