Mayfly Species Siphlonurus columbianus (Gray Drakes)

A large species, much resembling Siphlonurus occidentalis in its general appearance.

Head brown. Thorax deep brown. Mesothoracic scutellum blackish, with a paler ruddy spot directly anterior to it. Pleural sutures and wing bases yellowish. Fore legs deep blackish brown; middle and hind legs light yellowish brown. Femora marked with a slight purplish brown streak before the apex; tarsal joinings also purplish brown. Wings hyaline, with a faint brownish tinge in the stigmatic area. Veins entirely blackish.

Abdomen deep purplish brown dorsally, the pale anterior triangles light yellowish. Ventrally dull yellowish. The broad purplish brown oblique streaks are usually united on the anterior margin to form the blackish U-shaped marks. These are less distinct than in occidentalis, especially on sternites 8 and 9, where they barely join, are diffuse and poorly defined. Two tiny dark dots are usually present near the center of each sternite, within the dark U-mark. Segment 10 is wholly brown. Forceps dark with paler base. Penes as in fig. 122. Tails dark at base, becoming paler distally. Joinings brown.