Here is the fly pattern sheet for Pat Dorsey’s Mercury Baetis.
Materials
Hook:
Daiichi 1270 or Tiemco 200R #18-22
Bead:
Spirit River Hi-Lite Glass Bead Quick Silver (SL) Extra Small
Thread:
Light olive 8/0 Uni-Thread
Tail:
Black hackle
Body:
Superfine brown olive dubbing
Wingcase:
Black Zelon
Thorax:
Superfine brown olive dubbing
Here is a link where Pat Dorsey demonstrates how to tie the fly.