These are rather large mayflies, ranging from 12 to 18 mm in length. In the nymph, claws of the middle and hind legs are almost as long as the tarsus, while the front claws are shorter and forked. Three conspicuous stripes are located on the underside of the abdomen. The three tails are equal in length, with the middle one bearing long hairs on both sides and the outer ones bearing hair on the inner margins only. An outstanding feature of the adults are the heavily spotted fore wings, which are nearly three times as long as wide and contain two pairs of cubital intercalary veins. Adults have three tails and are generally brownish in coloration.