The Perfect Fly Big Slate Drake Dun is an excellent imitation of the adult stage of life of the mayfly. It imitates the mayfly as it drifts or floats on the surface, drying it wet wings enough to fly off the water onto the banks, bushes or trees where it will eventually change into the spinner stage of life. It even imitates the dun down to two or three tails and it two upright wings. It is fished on the surface as a dry fly. It should be treated with floatant.