Sometimes when it comes to an effective fly, simple is best. I call these flies simple nymphs, because they are very simple to tie and they just work. No wing cases, no legs, no ribs. Just a tail, well ya gotta gussy them up just a bit, (not to mention i love wood duck) and some dubbing tapered to a nymph shape. You can use any dubbin you wish. I havent used one yet that didnt work.
I fish these flies in multiple ways, they are very versatile. I fish one as a dropper. I have swung them, lifted them, I even grease the leader and fish these guys in the film. They make a great emerger that is well.... Just simple to tie.