Based on the opinions of some really good fishermen friends of mine, and borne out by my own experience, one of the keys to a successful nymph pattern is a dark and slightly bulging wing case. This, in many important species, is characteristic of the nymphs right before the wing case splits to release the wings.
Hook: Light wire dry fly hook, Sizes #14 - #18
Thread: Uni 8/0, rusty brown
Tail: Lemon wood duck
Rib: Fine copper wire
Abdomen: Pheasant tail fibers as herl
Wing case: Black turkey or crow tail slips, doubled

