Mayfly Species Isonychia intermedia (Slate Drakes)

A dark purplish red species, having pale antero-lateral triangles on the abdominal segments; venation dark brown.

Thoracic notum intense raw-umber brown, somewhat paler before the scutellum of the mesonotum. Fore leg about 2/3 as long as the body. Femur and tibia dark brown, femur rather paler at base; tarsus light brownish red, the first joint yellowish. Middle and hind legs light yellow, the claws and tarsal joinings narrowly purplish brown. Wings hyaline, venation dark brown; large longitudinal veins paler toward the wing base.

Abdomen intense purplish red. Tergites with yellowish white triangles occupying the antero-lateral angles, and between these and the median line another pale streak at the anterior margin. These spots increase in size posteriorly. Smaller pale triangles occupy the antero-lateral angles of the sternites. Sternite 10 and the forceps dull yellowish brown, washed with reddish purple; forceps base purplish red. Apical margin of the forceps base deeply excavated as in Isonychia sicca.