Mayflies are the most important group of insects to most fisherman, since the history of fly fishing relates primarily to them. There are over 700 species, but only a few are of importance to the fly fisherman.

 Mayflies like midges and caddis flies have four stages of metamorphosis. Egg, larvae, pupa, and adult. How ever the fisherman must be prepared with 6 basic patterns to successfully imitate the stage being eaten by the trout at the time. Mature mayfly nymph, emerging nymph, floating hatching nymph, stillborn Dun, Dun, and spinner.

This is one of the top "all purpose nymphs", which covers many insects. Anything with peacock herl seems to do the trick, and this one has the  popular goldhead.

These are pro tied on premium Mustad hooks