The nymphs are sprawling forms with bodies, legs and head that are strongly flattened. The head is large in relation to the body. Eyes are also large and are located on the dorsal surface of the head. Gills are present on abdominal segments 1 to 7. Adults have two tails and five freely moveable joints in the hind tarsus. Two pairs of cubital intercalary veins are present in the fore wings, while both fore and hind wings display heavy veination. The males have large spherical eyes that are normally light in coloration during the day and black at night.
Species of this genus range in size from 6 mm to 16 mm and are much more common in the East and Midwest; there are probably none in the west. Both the nymphs and adults of individual species vary considerably in coloration, making identification extremely difficult. Nymphs can best be recognized by the fact that gills on segments 1 to 6 are platelike, while the seventh pair is slender and threadlike. Adults are much more difficult to separate and usually require close examination under the microscope.