Mayfly Species Eurylophella bicolor (Chocolate Duns)

A member of the bicolor (now a synonym of Eurylophella bicolor) group; imago paler than other related species.

Head of male light brown. Thorax dark reddish brown. Legs pale yellow; coxae tinged with brown, and with black spots. Tinges of red may be present near the apex of each femur. Wings hyaline; venation hyaline. Stigmatic cross veins anastomosed. Abdominal tergites pale reddish brown with a distinct tinge of olive-brown. Blackish streaks near the pleural fold, and in some specimens a paler mid-dorsal line margined by interrupted blackish submedian streaks. Ventrally pale, the basal sternites slightly tinged with brown. Tracheae appear as fine dark lines. Tails pale yellowish white, the joinings purplish red.

Head of female pale yellow.

Nymph variable in both size and color. The occipital tubercles are wanting in the male nymph, and much reduced in the female. The rows of dorsal spines are distinctly divergent toward the rear, with a rather abrupt increase in the space between them on tergite 5. The spines on tergites 1-3 are short and chunky, and barely tapering. Postero-lateral spines on segments 2 and 3 are very poorly developed; these spines are well developed on the posterior segments, tipped with black and gracefully curved. The margins are set with short spinules, between which are long hairs. Color very variable, as is also the size. Pale specimens are strikingly marked with dark brown on the thorax and the posterior abdominal tergites. Legs distinctly banded. An oval patch is often present near the middle of the operculum. The usual four dots in a curved row, and the dark lateral dashes, are present in most specimens. Tails brownish, with indications of pale cross bands. Fore leg as in fig. 62e.