I have been tying and fishing this fly for many years, having first come across it while fishing the Catskill rivers some 30 years ago or so. I don't remember who introduced it to me, but I do know it has been a productive from the very first time I fished it. It's effective from late spring right through the fall, which coincides with the hatch cycle of the naturals - Isonychia bicolor. Because the naturals are on the water over a period of months, the trout get used to their presence, making this a good searching pattern during non-hatch periods, too.
Hook: #12 Dai Riki #125
Thread: 6/0 Danville olive
Tail/shuck: Brown antron or zelon
Body: Rabbit mix of burgundy, gray and brown
Wing: Deer body/comparadun hair
Easy to tie, and effective.