Slide a midge-size silver-lined glass bead onto the Tactical Midge hook and push it to the eye. The mercury in the name is the silver lining inside the bead. It imitates the gas bubble in an emerging midge pupa, so a plain glass or metal bead is not a substitute.
Start the white 70 denier flat thread behind the bead and wrap smoothly back to the bend. On a size 20 the thread is the entire body, so counter-spin the bobbin to flatten it and keep the turns touching with no overlap.
Tie in the small copper wire on the near side at the bend, then wrap the thread forward to the bead building a very slight taper, thicker at the front. That taper is all the shape a midge pupa has, and it reads clearly even at this size.
Spiral the copper wire forward in five to seven evenly spaced turns and tie it off behind the bead. Even spacing matters more than turn count here, irregular ribbing on a size 20 looks like damage rather than segmentation.
Helicopter the wire to break it rather than cutting it. A cut stub leaves a burr that catches on the glass bead and will eventually crack it.
Take two or three wraps of thread behind the bead to form a small collar, whip finish and trim close.
Other versions
1 more in the app: Mercury Midge: Fly Tying Recipes Recipe.