Mayfly Species Drunella cornuta (Large Blue-Winged Olives)

A species of the fuscata group (now a synonym of Drunella walkeri) allied to both E. cornutella (now a synonym of Drunella cornutella) and E. longicornis (now a synonym of Drunella longicornis); third forceps joint of the male relatively longer, and the second joint more strongly bowed, than in its immediate allies.

Head and thorax blackish brown. Pleural sutures, an area anterior to the wing root, and the antero-lateral margins of the mesonotum paler, with ruddy tinges. Femur and tibia of fore leg blackish brown, tarsus smoky brown. Middle and hind legs yellowish amber to olive brown. Hind femur very slightly longer than the tibia. Axillary cords extend backwards slightly beyond the scutellum, ending in blunt lobes. Wings hyaline, venation pale; the main veins of the costal margin often tinged with yellow basally, becoming yellowish brown apically. A brown spot at the base of the subcosta in the fore wing. Abdomen reddish brown dorsally and ventrally, the posterior segments darker; middle segments often with very narrow pale margins. Pleural fold may be narrowly pale. In some specimens there are faint traces of pale mid-dorsal and submedian streaks, pale ventral ganglionic areas and short brown submedian oblique streaks from the anterior margins. Tails pale yellowish. Our local form is slightly larger and paler than the one from Quebec. Specimens of the variety from North Carolina have wider pale areas on the abdomen; the abdominal tergites have darker transverse median bands and dark posterior margins; venation pale brown; tails purplish brown, size slightly larger than the New York form.

Described as E. depressa

Body length 6-7 mm, wing length 10-11 mm

A species of the fuscata group; very close to E. cornuta (perhaps it is synonymous with that species). Male imago not known. Female separated from that of cornuta, in original description, by the usual but not constant fusion of vein M and Cu₁ in the fore wing. Nymph said to be distinguished from that of E. cornuta by the shape of the maxillary palp and the fore femur. From the illustrations, we can find no good distinguishing character for the nymphs of the two species. Further, the venational character mentioned is one which occurs occasionally in several species of this group, and is apparently constant in none.

Head of nymph with curved frontal horns and a frontal shelf; no occipital tubercles. Thorax smooth. No dorsal abdominal spines. Gills borne on segments 3-7. General color reddish brown, the thorax often mottled with brown. Anterior margin of fore femur bears teeth or spines; the tibial spine or ‘thumb’ curves outward gradually from the base, and does not extend beyond the middle of the tarsus. Tails pale, with a single dark basal ring.