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.

The trees were leafing out and the trout were rising on this productive Wisconsin stream

From the Namekagon River in Wisconsin

Stream photos

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Female Skwala (Large Springfly) Stonefly Adult Female Skwala (Large Springfly) Stonefly Adult

Lateral view of a Female Skwala (Perlodidae) (Large Springfly) Stonefly Adult from Mystery Creek #308 in Washington

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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 Anafroptilum minor (Tiny Sulphur Duns)

Where & when

In 6 records from GBIF, adults of this species have been collected during July (50%), June (17%), September (17%), and October (17%).

In 1 record from GBIF, this species has been collected at elevation of 607 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.

Male Spinner

Described in Needham et al (1935) as Cloeon minor

Body length: 3 mm
Wing length: 3 mm

Abdominal tergites 2-6 of male imago hyaline; large lateral purplish brown blotches on each.

Head and thorax deep blackish brown. Anterior margin of metanotum tinged with purplish. Pleura and sternum largely dark; slight ruddy tinges anterior to the wing roots. Legs whitish; femora with traces of a ruddy median spot. Wings hyaline, venation pale. First cross vein of the radial sector considerably nearer the base of the wing than the following vein. Abdominal tergites 2-6 hyaline; geminate purplish brown dorsal dashes and large lateral blotches of the same color on each; on tergites 3 and 6 the lateral blotches coalesce dorsally, so that only the anterior portions of these are hyaline. Sternites 2-5 hyaline, each with a brown patch along the lateral margin on each side, and with transverse blackish dashes on the posterior margin, one on each side of the median line. Tergites 7-10 opaque, deep brown tinged with purplish; sternites light creamy brown, opaque; the posterior margin of sternite 9 shaded with purplish. Tails and forceps pale.

This species is distinct from all others thus far described, by reason of its small size and brownish abdominal blotches.