Members of this genus form the Gray Drake hatch in Michigan and are known as the Dark Gray Drakes in the West. The nymphs of Siphlonurus are streamlined, medium to large in size, and have platelike gills that are all similar in shape. Tails are fringed the same as Isonychia nymphs. Adult fore wings are long in relation to their width and the hind wings are well-developed. Both male and female are similar in coloration, being conspicuously marked with various shades of purplish-gray and reddish-brown. As in Isonychia, two tails are present in the adult stage.