Emergers are a major category of artificial flies! In cases when fish eat pupae that change under the water level in an adult, you rarely succeed with a different type of fly than with a close imitation of such an insect stage!
These flies are hung in a water film and the first part of the fly overlooks the surface, while the second part is sunk under the surface. Fly can sinks slowly, and if you hold the fly line in the stream, the fly starts rising to the water surface, perfectly imitating the movement of the live pupae!
Excellent and very effective patterns are the Shutlecocks, which imitate the hatching adults of the midges, the duns and the caddis. Once the fish feed on these insect stages, Shutlecocks are a very effective weapon for hungry trout and grayling!