It's a nice variant of the famous RS2 from Rim Chung.
A perfect mayfly emerger in smaller sizes between 14-20.
Hook: Ahrex FW511
Thread: Semperfli Nanosilk 18/0 Olive
Tail: Fibettes or Coq De Leon
Ribbing: UTC Wire Small
Thorax: Nature's Spirit Beaver Dry Fly Dubbing
Wing: Nature's Spirit CDC