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.