The Perfect Fly Winter Stonefly stonefly adult is the fully grown stage of life of the stonefly. It emerges from the nymph on the banks of the stream on rocks that protrude out of the water. The females return to the water late in the day to deposit their eggs and that is when trout dine on the adults. Fish the fly in the early afternoons until late in the day near the same water they emerged from. Floatant should be used on the dry fly.