Header image
Enter a name
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.

Dorsal view of a Kogotus (Perlodidae) Stonefly Nymph from Mystery Creek #199 in Washington
This one pretty clearly keys to Kogotus, but it also looks fairly different from specimens I caught in the same creek about a month later in the year. With only one species of the genus known in Washington, I'm not sure about the answer to this ID.
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.

Mayfly Species Baetis piscatoris (BWOs)

Where & when

In 1 records from GBIF, adults of this species have been collected during June (100%).

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.

Male Spinner

Body length: 6 mm
Wing length: 6 mm

Abdominal tergites 2-6 of, male imago yellowish hyaline, a purplish red band on posterior margin of each; genitalia of the moffati type (now a synonym of Baetis tricaudatus).

Head and antennae reddish brown. Turbinate eyes moderate in size, on a rather high stalk; stalk yellowish, upper surface light orange, in alcoholic specimens. Thorax rather dark reddish brown; a yellowish streak on mesonotum anterior to wing root, another along postero-lateral margin; a small yellow area anterior to the scutellum; margins of scutellum blackish. Intersegmental areas of pleura yellowish red. Fore legs light yellowish brown; middle and hind legs yellowish, joinings and tips of tarsi light brown. Wings hyaline, venation pale; longitudinal veins of costal margin faintly yellowish. A faint whitish cloud in stigmatic area of fore wing; 8-11 cross veins, aslant, sometimes incomplete, occasionally anastomosed; with granulations between them. Intercalaries of the first and second interspaces may be single or paired; shorter than the following pairs. Hind wing rather large; three longitudinal veins; costal projection well developed. Usually traces at least of two intercalaries between the 2nd and 3rd veins; often also a faint intercalary between veins 1 and 2.

Abdominal tergites 2-6 yellowish, hyaline; on the posterior margin of each is a prominent purplish-red band, not extending to the spiracular line. Tergite 2 is often slightly tinged with brownish. Sternites 2-6 paler yellowish. Spiracular area outlined by a geminate purplish line, from which on each segment arise lateral branches to tergite and sternite. Segments 7-10 opaque, light reddish brown, the margins narrowly darker; sternites only slightly paler than tergites. Tails pale yellowish brown, paler at tips. Forceps yellowish.

In type of genitalia, this species is allied to the pale B. lasallei (now a synonym of Baetis intercalaris) and to the yellowish-brown Baetis adonis, from both of which it may be distinguished by the prominently banded abdomen; other species having the same type of abdomen are darker in coloration (Baetis tricaudatus, of the color of which we are not certain, is a larger species). B. cingulatus (now a synonym of Baetis phoebus), which has a similarly-marked abdomen, has genitalia of the Baetis intercalaris type.

Female Spinner

Female reddish or orange-brown; legs yellowish brown, tarsi somewhat darker. Venation light reddish brown. Abdominal sternites yellowish; tergites banded as in male. Spiracular markings prominent. Tails as in male.

Start a Discussion of Baetis piscatoris


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

Mayfly Species Baetis piscatoris (BWOs)

Species Range
Troutnut.com is copyright © 2004-2024 (email Jason). privacy policy