Poly yarn or Antron (post) White or dun poly yarn antron (small clump)
Microfibbets or extended-body foam/dubbing Olive ice dub (few fibers / small strip)
Dry fly dubbing Olive ice dub (pinch)
How to tie it
Lay a thread base to the bend.
Build the extended body off the back of the hook: dub a slim tapered olive abdomen over a fine needle or split-thread wisp, or fold a thin olive foam sliver, so it projects about one shank length past the bend with two or three split microfibbet tails at the tip.
Bind the extended body firmly at the bend and advance thread to the 65% mark.
Stand an upright post there with criss-cross turns and a front thread dam.
Dub a slim olive thorax fore and aft of the post; go sparse for the tiny BWO silhouette.
Tie in the blue dun hackle at the post, wind 4-5 turns down the post, and secure.
Sweep the hackle up, whip finish at the eye, and add a tiny drop of cement to the post base.