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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

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.

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 Baetis bicaudatus (BWOs)

Baetis bicaudatus is a western taxon of some local importance.

Where & when

In 9 records from GBIF, adults of this species have been collected during June (33%), April (22%), July (22%), March (11%), and August (11%).

In 55 records from GBIF, this species has been collected at elevations ranging from 20 to 11037 ft, with an average (median) of 5354 ft.

Species Range

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

Body length: 4.5 mm
Wing length: 6.5 mm

Only the female imago of this species is known. Body uniform light brown. Hind wing with two veins only; the third entirely wanting, according to the original description. Costal projection present, quite prominent.

Described as B. minimus

Body length 5 mm, wing length 7.5 mm

Only the female imago is known, hence the position of this species in reference to others of the genus is uncertain. Species said to be much like moffati (now a synonym of Baetis tridcaudatus), but differing in the small size of the body in relation to the fore wing, and of the hind wing in relation to the size of the fore wing. Hind wing rather small (0.8 mm.), the third vein present but very faint; no intercalaries. Costal projection present near the base of the hind wing, moderately developed. No color characters are given.

Specimens of the Mayfly Species Baetis bicaudatus

6 Nymphs

Start a Discussion of Baetis bicaudatus


  • Caucci, Al and Nastasi, Bob. 2004. Hatches II. The Lyons Press.
  • Needham, James G., Jay R. Traver, and Yin-Chi Hsu. 1935. The Biology of Mayflies. Comstock Publishing Company, Inc.

Mayfly Species Baetis bicaudatus (BWOs)

Species Range
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