Mayfly Species Callibaetis fluctuans (Speckled Duns)

A brownish white species; cross veins of fore wing relatively few in number; marginal intercalaries single; wing of male not pigmented.

Head and thorax brownish white; vertex of female sometimes ferruginous, “with a double longitudinal carina.” Antennal filament dusky, sometimes pale at the base, a double light brown band on the thoracic notum, confluent behind. Legs whitish, the tips of the tarsi cloudy. Wings hyaline, iridescent; veins rather coarse near the base; longitudinal veins generally brown, and occasionally edged with brown toward the base. Cross veins fine, always hyaline. In the wing of the female, the space between costa and subcosta is hyaline; on the costal margin are 15 to 18 small brown spots, some of these confluent. A light brown band is present behind the subcosta, containing about 14 round hyaline spots—“some of them confluent before or behind with the hyaline part of the wing.” Posterior margin of this brown vitta variable, irregular; sometimes with 6 or 7 “large obtuse teeth.” Marginal intercalaries occur singly. Cross veins behind the vitta relatively few in number (14 to 18, according to Walsh).

Abdomen, both tergites and sternites, generally brownish-white, sometimes varied with brown. Two of Walsh’s specimens were pale brown, the 6th segment brown. Tails whitish. (Original description, of female only). The wing of the male (if we are correct in the identification of this species) is unpigmented. In both sexes, brown submedian curved marks are present on tergites and sternites.