NYMPH FLIES Nymphs represent insects in their under water aquatic life stage. This stage comes before the adult stage where the insects emerge out of the water and fly away, normally to mate and lay eggs (dry fly). Technically the term 'Nymph' means the juvenile stage of a Mayfly but it is commonly used to refer to any insect in it's aquatic life stage. Nymphs are, perhaps one of the most deadliest ways of taking most species of freshwater fish. In a river or stream, they can be fished anywhere from just beneath the surface to imitate emerging or drowned flies to right to the bottom to imitate the unhatched larvae. The Nymph of the march Brown stick to rocks and like fast flowing water.