Beautiful rendition of Brachycentrus numerosa. The Beaverkill has an amazing emergence of these caddis flies. They emerge in what I call "waves". You'll see a blizzard of adults emerging and flying upstream for about 5 - 10 minutes. Then there will be a flat period, or lull, for up to an hour then another wave will emerge and start flying upriver.
If the West Branch has these caddis I'm never there when they emerge. But it does have stellar emergences of Brachycentrus appalachia (Apple Caddis) and many large browns will rise, or boil, during this emergence. In my experience most fish are boiling to pupa swimming up in the water column and are either in a drift or about to break through the surface tension.
I fish an adult but trail it with a pupal form. Most fish are hooked on the pupa. I couldn't get the right light on the adult but if anyone wants the recipe just PM me.