This is a super-simple pattern. If you seek an effective, quickly tied dry fly, then look no further. I find these most useful tied on size 18 hooks and smaller. If you are new to tying with CDC then this is a good pattern to try.
They sit beautifully in the water: the wing above the surface and the body hanging beneath. The abdomen of the fly has a segmented appearance.
It works well as an olive emerger, drowned dun or a terrestrial pattern. Play about with size and colour and try dubbing the body. The tutorial opposite is the fly in its most simple form - just thread and two or three plumes of CDC.
Fly tying at its most basic... but also most efficient!
Hook: Partridge SLD #18 and smaller
Thread: Sheer 14/0, grey
Wing and body: CDC, two or three plumes
A version woth a dubbed body:

The CDC Shuttlecock, having done its job:

For the more experienced tyer, or if you wish to experiment with CDC Emergers, then I offer another tutorial for a super effective pattern: here
