During a mayfly hatch many mayflies get stuck in the film. They either die or just cant get out of their chucks. When you can´t figure out what the fish feeds on it is usually this stage of the mayflys cycle. The fish uses a lot less energy compared to targeting nymphs or fully grown insects. The ones pictured here uses a wing of either deer hair or snowshoe rabbit. You can also use cdc, but I prefer the first two alternatives. The best alternative for the body is twisted marabou. Tie the imitation in any colour to match the hatch in your local stream or lake.