Hareline Cul de Canard
Few materials are as versatile as CDC. With these feathers, you can tie wings on emergers, dry flies, terrestrials, and even spinners, but you can also strip the fibers off of the stem and work them into a dubbing loop, use the feathers to wrap naturally buoyant bodies, and you can even use CDC to tie nymphs that, when in the water, have a great trapped air effect.