Slide a 7/64 UV white bead onto a size 12 curved nymph hook and lay down a quick underbody of Uni-Stretch, running it down the shank and back, then whip finish and cut it off. On a hook this size that saves you a great many thread wraps later.
Start rusty brown 70 denier thread, cover the Uni-Stretch and run down to just short of where the Uni-Stretch ended.
Tie the brown stretch floss in below the step left by the Uni-Stretch rather than on top of it, then squeeze it up as you bind it. That single change smooths out the bump instead of adding to it. Pull harder on the floss the further down the bend you go so it thins out at the rear.
Tie one strand of root beer buzzer wrap in right at the back, then wrap the thread forward in tight turns to cover all of the stretch floss and Uni-Stretch and finish the taper. You want the rusty brown covering everything, because the buzzer wrap is translucent and takes its colour from what is underneath.
Wind the buzzer wrap forward up the shank without overlapping, tie it off securely behind the bead and trim.
Bring the stretch floss forward as the rib, pulling it fairly snug on each turn so it thins into a clean segment line, tie it off tight, give it a good pull and trim so no tag is left.
Spin the bobbin to flatten the thread, finish the thorax, whip finish and coat the whole fly to make the colours pop.