Mayfly Species Eurylophella aestiva (Chocolate Duns)

A member of the bicolor group, very close to E. bicolor (now a synonym of Eurylophella bicolor). Imagos are difficult to separate from that species.

Imago very similar to a large specimen of E. bicolor. Thorax somewhat darker brown than in that species. Legs light yellow. A dark spot on the side of each coxa; traces of dark median banding on the middle and hind femora, and a slight dark terminal streak on each. The first seven abdominal tergites are an even dark brown; the apical three, bright brown. A paler mid-dorsal stripe, enclosing a narrow dark median line, and margined by dark submedian streaks, may be present. Sternites 1-7 subhyaline, the basal three tinged with brown. Sternites 8 and 9 are whitish, opaque, and shaded with light brown. The usual curved row of four dark dots is more or less well developed. Tails pale, the joinings reddish brown. Genitalia of the usual type in this group.

The nymph has occipital tubercles rather well developed in both sexes. The femora are relatively short and chunky, the posterior margin of the hind femur being only slightly more than twice the greatest width. Rows of dorsal tubercles subparallel; those on tergites 1-3 are moderately long, rather narrow, blunt and tapering. The spines on segments 2 and 3 are poorly developed, being however slightly stronger than in E. bicolor (now a synonym of Eurylophella bicolor). The margins of the lateral extensions bear many spinules, but are practically without the long hairs found in bicolor. General color dark brown, sprinkled with pale dots; traces of a pale mid-dorsal line margined with dark submedian streaks usually present. Legs dark brown with pale banding, which is reduced to small oval spots on the femora. Operculum sprinkled with pale dots, and with a pale median oval patch. Short dark lateral dashes and the usual curved row of four dark dots are usually present on the abdominal sternites. Tails dark brown, banded alternately with yellow.