This is a classic American wet fly, named for Dan Cahill. Ray Bergman wrote in Trout, “If it was necessary to confine my assortment of flies to only two or three, this would be one of them. Basically, it is an Eastern pattern, particularly effective in the Catskill waters and similar Eastern mountain streams.”
High praise indeed. I’ve been fishing this fly with great success for years. So when creamy mayflies are coming off on the Farmington — or any river for that matter — the Light Cahill winged wet is usually the first fly I’ll tie on. There’s something about wood duck that states “buggy” and “alive” in no uncertain terms. I usually fish at least two of them on a dropper rig, and look to target specific rising fish. Trout will hit the fly on the dead drift (mend your rig like you would a dry) and at the drift’s end. Just let the flies sit there – and hold on. Some of the most violent takes I’ve ever experienced while trout fishing have come on this fly.
Tying notes: Sometimes I tie this fly with a tail of wood duck or partridge, or substitute partridge for the hackle. Sometimes I’ll add a gold rib. While all these iterations work, the fly pictured here on a 2x strong hook is the one I fish the most. I like to keep the body sleek and tapered, so no dubbing loop. It’s a pretty straightforward tie, and you can crank out a bunch in a short time. I’ve seen some versions of this fly where the hackle is clipped off the top half of the fly, but I leave it on. I tie the wing in last.
currentseams.com 
Steve, this fly looks killer. I am gonna have to tie some of these. Thanks for sharing it with us!
One of the first wet flies I learned to tie and one that has always produced. I first started tying it because I take a lot of wood ducks each fall so I always have an ample amount of feathers. These days I tie it because it works.
I love those Catskill patterns too, Classic….
Fantastic fly!
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