Mayfly Species Drunella coloradensis (Small Western Green Drake)

A species of the fuscata group (now a synonym of Drunella walkeri); closely allied to E. flavilinea (now a synonym of Drunella flavilinea), from which the imago may be distinguished by the dark venation and the straighter second forceps joint, which is not swollen apically.

Imago dark brown, without striking color markings. Thorax dark brown. Venation dark purplish brown. Abdomen rather uniform dark brown; pleural fold pale; margins of segments pale, appearing as light bands when the body is extended. Tails dark brown, deeper brown at the base. Apical margin of forceps base almost straight between the bases of the forceps limbs. Second joint of forceps moderately and regularly curved, not noticeably swollen near the apex; somewhat thinner near the middle than elsewhere.

Nymph with very low occipital tubercles; tibial ‘thumb’ longer and sharper at the tip than in flavilinea(now a synonym of Drunella flavilinea) ; middle and hind legs relatively more slender; dorsal spines more prominent.

Nymph without frontal horns or frontal shelf. Head roughened; occipital tubercles present, but very low and inconspicuous. No thoracic spines. Anterior margin of the fore femur with teeth or spines. Tibial ‘thumb’ quite long, sharp-pointed, relatively straight. Legs stout, but relatively more slender than in flavilinea; all femora somewhat flattened, the posterior margins with many hairs and a few short spines. Gills borne on segments 3-7. Dorsal spines present on tergites 1-9, somewhat longer on tergites 6-8 than on the basal segments. General color light brown, mottled with paler areas, especially on the legs. Tails each with two dark and two paler bands.