The mayfly for trout fishing is a late spring early summer fly, when the adult dies after mating it lies on the water surface in the spent position, these are tied to imitate that stage and are very effective. The Mayfly is taken by trout very readily, watch the mayflies darting around the water looking for a mate, this is when the trout feed from the mayfly. The mayfly will lie on the water surface and provide the perfect meal for the trout. Try also the drake trout flies at the same time, fish in the same manner as the mayfly.