Here in the Rocky Mountain west we often get an amazingly prolific hatch of large drake mayflies, in both gray and olive-green. When the drakes are hatching the trout go bonkers for them and come to the surface with abandon. The Hair Wing Drake floats well and matches the large drakes during a hatch but it also will work as an attractor or a "searching" pattern. Both colors available in size 10 & 12.
TIP: This pattern will float a medium sized nymph or emerger in a dry-dropper rig. Don't hesitate to try a size 14 about 24" below it.