The CDC Emerging Mayfly Nymph is a great pattern to use in the spring, summer, and fall, and can be tied to look like a number of different mayfly species. We use it most often as a PMD imitation, and have great luck with it on our local tailwater. Tie it to match your local bugs, you won't be disappointed!  

Materials:

Hook: Daiici 1560
Thread: Tiemco 16/0 Olive or Lt. Cahill Thread
Tails: Coq de Leon
Abdomen: Pale Yellow CDC
Rib: Silver Ultra Wire
Wing Case: Black 2mm Foam Strip
Thorax: Pale Yellow CDC