Mayfly Species Acerpenna pygmaea (Tiny Blue-Winged Olives)

Abdominal tergites 2-6 of male imago hyaline whitish; genitalia of the Baetis intercalaris type; hind wing with two veins only (see fig. 163).

Turbinate eyes moderately large, oval; deep brown; upper part of stalk yellow, basal part blackish. Face black; light green shading at base of antenna only. Antenna black, a white ring at the apex of the first joint. Thorax shiny black; faint pale markings along the pleural sutures. Legs white; fore femur slightly smoky. No granulations between the cross veins of the stigmatic area of the fore wing; no intercalaries in first interspace. Hind wing with two veins only, the third entirely wanting.

Abdominal segments 2-6 hyaline whitish; tergites 7-10 light sepia brown ; sternites opaque white. Black dots over the spiracles. Tails white. A tubercle on inner apical margin of the first forceps joint is well developed.

Described as B. harti

Body length 2.5 mm, wing length 3 mm

Abdominal tergites 2-6 of male imago hyaline whitish; genitalia of the Baetis intercalaris type; only two veins present in hind wing, the costal projection very prominent.

Turbinate eyes large for size of insect, oval, blackish brown. Head blackish. Thorax deep black-brown. Legs pale yellowish. Wings hyaline (venation pale?). Intercalaries of the fore wing short but distinct; the first pair obsolescent. Hind wing narrow and long, with a prominent costal projection, much as in B. quilleri (now a synonym of Fallceon quilleri). Only two veins, the third entirely lacking.

Abdominal segments 2-6 hyaline whitish; segments 7-10 chocolate brown dorsally, the sternites slightly paler. Black dots along the spiracular area. Tails whitish. Genitalia of the intercalaris type.

This very diminutive species is distinguishable from B. pygmaeus (now a synonym of Acerpenna pygmaea) by reason of the prominent costal projection of the hind wing; from B. akataleptos (now a synonym of Acerpenna akataleptos), which has a similarly prominent costal projection, it is separable by the pale basal abdominal segments, which in akataleptos are dull brown.