Mayfly Species Isonychia velma (Slate Drakes)

A large reddish plumbeous species with bicolored legs and fine dark spots on the wings.

Head reddish brown; antennae and median carina darker. Median carina purplish red, likewise the frontal margin. Thorax reddish brown; many sclerites are edged with whitish, and the notum is more uniformly brown. Fore legs reddish, the tibia darker, the femur paler at the base. Middle and hind legs reddish on the coxae, the outer half of the femora and the tarsi; basal half of femora, and tibiae, pale yellow. Fore wing with a roseate tinge along the costal border; a touch of the same color at the extreme anal angle of both wings. Hind wings of male with a faint brown border around the outer margin, which is almost obsolescent in the female. Longitudinal veins brown. Cross veins of the subcostal and radial spaces of the fore wing, and the costal cross veins more faintly, bordered with reddish brown to form diffuse darker spots. Remainder of wing hyaline.

Abdomen reddish plumbeous with obscure pale mid-dorsal and mid-lateral stripes margined by brighter plumbeous, forming interrupted lines. These are darker and confluent on segment 9. “The large thin flat lobes on the side of segment 9, and the apical ventral pair at its apex, are translucent.” (Needham). Posterior margins of all segments dark. Pleural fold margined above and below by a darker strip. Sternites marked with an obscure paler mid-ventral stripe, margined posteriorly by dark sub-median streaks based on the posterior margin. Tails of the male whitish, at base tinged with red. Forceps base and forceps of male brown, as are also the penes. The latter are somewhat of the albomanicata type (now a synonym of Isonychia bicolor); the forceps base deeply excavated apically.

In the female, the top of the head is largely reddish, the median stripe paler, the corners of the occiput darker. Hind wings of male with a faint brown border around the outer margin, which is almost obsolescent in the female. In the female, the tails are yellowish, and more distinctly red at the base. Subanal plate of female very deeply excavated at its apical margin, the outer angles acute.