Mayflies

The life cycle of a mayfly begins when the eggs laid on the water by a female mayfly; an activity that most commonly takes place in the evening, and to a lesser extent, morning hours. Small mayfly nymphs hatch out of these eggs, spending a long portion of their lives about one year under water as a nymph until the end of this cycle approaches. This is when the nymphs hatch an achieve per-adult status, which can happen in two different ways: One method is for the mayfly to swim up and attach itself to the surface film, where the nymph will shed its shuck or case and emerge as a winged dun. In addition some species of mayflies emerge on stream bottom. Upon completing this they rise to the surface as full-blown winged dun’s.
The wings of a mayfly dun are gray in color during this phase of life hence the name. After emerging is complete the newly hatched bug will float on the surface of the stream until the wings are dry and will take flight to stream-side brush or trees to undergo its final molt. After one or two days, the mayfly will go into its final transformation into the adult mayfly. Shedding its skin for what is often an entirely new body color, and wings that are now clear.
When molting is done, the mayflies take flight into the air to mate in midair. After mating, the male mayflies will die, spinning down towards the water laying dead in the surface film. The females will return to the water to lay eggs and die themselves.