Nymphs require clean unpolluted water, and live in riffles with water currents ranging from medium to fast. Male duns are easy to identify because of their large eyes, and light brown back. Hatches of these little sulphur oliveish colored mayflies are sometimes a big factor in the fall, with heavy evening hatches in early September. Nymphs move to slow to medium currents just before hatching. As the hatch begins hebe nymphs swim toward the surface shedding their husk on the way up. Fishing a wet fly imitation can be effective during the beginning of the hatch.