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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.

Lateral view of a Clostoeca disjuncta (Limnephilidae) (Northern Caddisfly) Caddisfly Larva from the Yakima River in Washington
This one was surprisingly straightforward to identify. The lack of a sclerite at the base of the lateral hump narrows the field quite a bit, and the other options followed fairly obvious characteristics to Clostoeca, which only has one species, Clostoeca disjuncta.
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 phoebus (BWOs)

Where & when

In 26 records from GBIF, adults of this species have been collected during July (54%), June (35%), and August (12%).

In 20 records from GBIF, this species has been collected at elevations ranging from 3 to 6535 ft, with an average (median) of 417 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.

Male Spinner

Body length: 5 mm
Wing length: 5.5 mm

Abdominal tergites 2-6 of male imago hyaline whitish; genitalia of the Baetis intercalaris type, the tubercle on the inner apical margin of the first forceps joint well developed.

Turbinate eyes large, almost circular, with long stalk; in living specimens, red-brown with a narrow yellow rim. Head and thorax brown. Along the lateral margin of the mesonotum, forward from the wing roots to the anterior projection, is a yellow streak; yellowish brown shading on the posterior portion of the mesonotum and the anterior area of the metanotum. Pleural sutures marked more or less with ochreous. Legs very pale yellowish. Wings hyaline, cross veins pale. Intercalaries of the fore wing well developed, those of the first pair not longer than the following pairs. Hind wing broad, well developed; third vein extends rather beyond the middle of the hind margin; a short intercalary usually present between veins 2 and 3 (see fig. 163).

Abdominal tergites 2-6 hyaline, whitish, very faintly tinged with olivaceous; 7-10 bright ruddy brown. Sternites opaque whitish, variably tinged with brown. Slight blackish dots along the spiracular area. The tubercle on the first joint of the forceps well developed.

Close to Baetis flavistriga, but larger, and with larger turbinate eyes. Also distinguished by the paler basal abdominal tergites, which are much less shaded with olive than in that species. It is likewise very close to B. pallidulus (now a synonym of Callibaetis pallidus), but with somewhat smaller eyes, which in life are red-brown, not light orange as in that species.

Described as Baetis cingulatus

Body length 5 mm, wing length 5.5 ml

Abdominal tergites 2-6 of male imago pale yellowish white, narrowly ruddy on the posterior margins; genitalia of the Baetis intercalaris type.

Turbinate eyes large, deep brown in color. Face and antennae black-brown. Thorax deep olive brown. Lateral margin of mesonotum anterior to the wing roots frequently yellowish; scutellum whitish, often with ruddy tinges anterior to it; ruddy tinges on the pleura, the sutures pale. Anterior margin and projecting median portion of metanotum whitish. Legs pale yellowish; fore femora mostly pale brownish, as are the tips of the middle and hind ones. Wings hyaline, venation pale. First pair of intercalaries of the fore wing well developed, but not as long as in B. intercalaris, second pair shorter than the first or third pair. Hind wing slightly more than twice as long as its width. Third vein well developed, reaching to the middle of the hind margin. Intercalaries absent, or with a trace of one between the second and third vein.

Abdominal tergites 2-6 pale yellowish white, semi-translucent; the posterior margins narrowly ringed with reddish brown, which color may extend forward laterally over the posterior portion of each tergite. Segments 7-10 opaque, light reddish brown dorsally, the sternites whitish tinged with brown. Sternites 2-6 pale whitish. Tracheae blackish in the spiracular area, forming a more or less continuous wavy dark line. Tails and forceps white. Genitalia with a well-developed tubercle on the inner apical margin of the first joint. The dark bands on the posterior margins of the basal abdominal tergites separate this species from the allied Baetis phoebus.

Start a Discussion of Baetis phoebus


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

Mayfly Species Baetis phoebus (BWOs)

Species Range
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