One of the original North Country Spiders, the Waterhen Bloa soft hackle was introduced in the Yorkshire area (Northern England) and has been a successful wet fly for over 200 years. Originally tied with hackle from a waterhen, many modern tiers will substitute starling for the bloa color (blue/medium dun).
Hook: #10-16 wet fly
Thread: Yellow (originally Gossamer silk)
Dubbing: Muskrat (or mole hair)
Hackle: Waterhen (or starling)
This pattern can be found in:
“Essential Trout Flies,” by Dave Hughes. https://amzn.to/3lbCZYX