Mayflies spend the majority of their lives as nymphs on the stream bottom. When the time is right (depending on the species), they emerge with members of the same species into the adult dun stage. A short time later they molt into the sexually mature spinners. The male and female spinners mate and the females return to the water to deposit their eggs. They have then completed their life-cycle and many fall to the water’s surface as spent spinners. All of these stages (nymph, emerger, Dun, and spinner), are important to trout and the fly angler.