Mayfly

There are over 3000 different species of mayflies. Their adult stage is characterized by their wings that look like very fragile sails on a sailboat. When adults, their lives are short lived. When they become adults they usually have a day or two to mate and then they die. When the adult emerges from the water it is still “sexually” immature and is called a Dun. The mayfly dun’s wings are usually opaque and they will fly off to molt again into a sexually mature mayfly. The mature adult or Spinner has wings that are clear. Once mating has taken place the female lays her eggs and both the male and female die. These mayflys are referred to as “spent” and lie flat on the water surface with their wings out stretched. When the eggs hatch on the bottom of the river the mayfly becomes a nymph and could live in this stage for up to two years. Most mayfly nymphs fall into two categories – clingers and crawlers. When the nymph knows it’s time to emerge and become an adult it will swim to the surface.

Here is a video to help you understand the Mayfly and gain valuable insights on how they behave and what they really look like to the trout. 
This excerpt was taken from the Bugs of the Underworld by Ralph and Lisa Cutter. Look online if you are interested in purchasing their DVD.