This genus is common from East to West. The nymphs remain buried in the stream bottom, except during the molting periods, which take place up to thirty times before emergence. Nymphs leave the bottom, swim about, then rebury themselves after molting. It is this habit that gives trout a chance at them all year long. They are found in the trout's stomach even in the winter months.
Nymphs are moderate to large in size, have a deeply forked frontal prominence, and mandibular tusks that are smooth and slender. Adults display prominently spotted wings and three tails of equal length.