Griffith's Gnat
Note: Although the fly in the photo is a size 16, the most common size for fishing is a size 20. The hackle on this fly was "reverse palmered", that is, it was tied in behind the eye and wrapped back to the bend of the hook. After the hackle was tied off, the thread was wound foward through the hackle and a small head was created. Hans Weillenmann suggested that I tie a GG in this fashion, and I've never looked back.