This fly put together by Ernie Borcher of Michigan in the 1940's or very early 1950's is called Boucher's Special. I've also seen it referred to Borcher's Drake. It can imitate a number of the darker mayflies. The body was originally tied with Condor Quill but today Turkey is used. Tied in sizes 14-18 for the early season mayflies like the Hendrickson and sizes 10-12 for the big later season mayflies.