After hatching, a nymph lives on a stream or river bottom up to a year (depending on species) and then begins the process of transforming into an adult fly. The nymph rises ("emerging") to the top of the water where it will continue to develop, molting into an adult fly ("dun" stage). Once mature (spinner stage), it will take flight and mate. The females will return to the water to drop their eggs before falling to the water's surface as a "spent spinner". Sad...but true.