The pheasant tail nymph (PTN) is used to represents a wide range of aquatic insect larvae and can even be used to imitate fish fry. It’s useful on still water and running water for targetting numerous species though originally it was dressed for trout in theRiver Avon. The PTN is especially good at representing darker species and is considered an especially good match for the nymph of the Blue-winged Olive. On a 2X hook shank it works well as a stonefly. To imitate lighter nymphs you might do better with a Gold Ribbed Hare’s Ear.
How to fish:
In still water present the PTN using a slow hand-twist or use a wind drift. In running water use standard nymph tactics (drag free drift, rising nymph, wetfly swing).