Mayfly Species Isonychia rufa (Slate Drakes)

A rather bright red species, with pale venation. Eyes ruddy chestnut in living male. Head light brown, bases of the ocelli black-ringed. Thorax ruddy brown. Coxae and femora of fore legs deep reddish; tibiae blackish; tarsi dull yellowish white, the apical portion of each joint shaded with smoky. The tarsus is as long as the tibia; the whole leg is somewhat longer than in Isonychia sicca. Middle and hind legs rather deep yellowish. A small black lateral spot on the occiput. Wings hyaline, with pale venation in the male.

Abdomen bright reddish dorsally, paler and duller ventrally. No blackish shading except a narrow posterior margin on each segment. Tails whitish yellow; traces of reddish rings in the basal joinings. Forceps pale reddish brown. Forceps base deeply excavated on its apical margin. Lateral arms of the forceps base rather broad, the inner margins wide and flaring, somewhat angulate apically. Penes of the albomanicata type (now a synonym of Isonychia bicolor).

Head of female pale yellow, shaded with brown around the bases of the ocelli and between the eyes and the lateral ocelli.
Wings hyaline; in the female, the cross veins may be faintly tinged with brown. Subanal plate of the female deeply excavated apically, its outer angles acute.