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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 Callibaetis pallidus (Speckled Duns)

Where & when

In 2 records from GBIF, adults of this species have been collected during June (50%) and September (50%).

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

Described in Needham et al (1935) as Callibaetis semicostatus
Body length: ?-9 mm
Wing length: 8-10 mm

A brownish species; cross veins of fore wing moderately numerous; marginal intercalaries paired; wing of male pigmented.

Body of male brownish, with fine dots on many parts, particularly the venter. Some of the thoracic sutures are whitish. Legs pale, darker at tips of tarsi; femora without freckles. Wings hyaline. Longitudinal veins brownish, in the type specimens, although the original description states, “veins pale.” Wing of male pigmented, the vitta bounded in front by the subcosta and behind “by the fourth vein”; it is light brown or reddish brown in color, and extends halfway from the base to the tip of the wing. Two or three pale dots are present in this vitta; sometimes there are also a few dark marks in the costal areas. One of us (Needham) studied the type specimens, adding these notes; “Subcostal pale brown strip shows fenestra faintly near the base; vitta overspreads the stigmatic area more or less; stigmatic cross veins more or less irregular, very oblique.” Hind wings fully twice as long as broad, angulate at the base. Abdominal sternites finely dotted. Tails white.

Described as Baetis pallidulus

Body length 4-5 mm, wing length 5 mm

Abdominal tergites 2-6 of male imago very pale yellowish hyaline; genitalia of the Baetis intercalaris type, tubercle present on inner margin of basal forceps joint.

Turbinate eyes very large (larger than in B. intercalaris), circular; deep reddish in dried specimen, light orange in living insect. Thorax pale yellowish olivaceous to light red-brown; scutellum of the mesonotum creamy. Legs pale yellowish. Wings hyaline, venation pale. Marginal intercalaries of fore wing well developed; those of the first pair not longer than any of the others; the pair in the second interspace somewhat shorter than the 1st or 3rd pair. About 8 stigmatic cross veins; aslant, somewhat anastomosed; few or no granulations between them. Hind wing broad, very similar to that of B. moffati (now a synonym of Baetis tricaudatus); usually one somewhat oblique intercalary between the 2nd and 3rd vein.

Abdominal segments 2-6 very pale yellowish, hyaline, not tinged with olivaceous. Tergites 7-10 light red-brown; sternites deep creamy, sometimes with faint reddish-brown tinge. A pale-centered black dot over each spiracle, and traces of a continuous dark spiracular line. Tails whitish. A tubercle present on the inner margin of the basal forceps joint.

The species seems close to Baetis phoebus, but is apparently distinguishable from it by the larger eyes, which in life are light orange instead of red-brown; the basal abdominal tergites are likewise paler, and the 2nd pair of marginal intercalaries relatively shorter, than in that species.

Female Spinner

Body length: 9 mm
Wing length: 10 mm

A pale ferruginous species; cross veins of fore wing numerous; marginal intercalaries paired; male undescribed (wings unpigmented?).

Thorax pale ferruginous. Femora pale, not freckled; tarsi blackish. "Costa marked with brown and white; vitta pale ferruginous, extreme basal costal space hyaline, vitta with a number of hyaline spots, especially near the pterostigmatic region, hind edge with several broad indentations, especially on basal half" (Banks). Cross veins of fore wing numerous, most of them white; marginal intercalaries occur in pairs, in the type specimens. Abdomen pale ferruginous. Tails pale, unmarked.

Start a Discussion of Callibaetis pallidus


Mayfly Species Callibaetis pallidus (Speckled Duns)

Species Range
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