When trout are keying on small mayflies, it is easy to confuse the dorsal/tail surface bulge with the slurp of surface grab. As long as the emergers are in abundance, trout are likely to continue to feed on these more vulnerable bugs. This is why a fly like the Emergence can often out-fish a dry fly in the course of a hatch.
These small flies require light tippets on long leaders. If the fish are bulging at the surface, tie on an Emergence to match the natural color of the bug. Dress the fly with floatant and cast into the ring of the rise.
Tie the Emergence on a No. 14-18 dry-fly hook. For the tail, use Z-Lon. Wrap the body with Superfine olive dubbing or to match the natural. For the legs, use dun-hackle fibers tied along the body. Tie in a dun CDC puff for the wing. Finish with a Superfine dubbed head.
—Gary Lewis, For The Bulletin