Lay a base of black thread from behind the eye to the bend. On this fly the bend is the crawdad's head, so the claws go on at the bend and the fly finishes at the hook eye.
Stack a small clump of red squirrel tail, measure it at least a body length, and bind it in on the far side of the shank at the bend with a couple of wraps as tight as you can without spinning it. Take a few loose wraps forward over the butts, then tighter wraps back.
Take a few wraps around the base of that clump alone, as you would post a parachute, so it stays bunched. Push it round to point out to the side and lock it with a few tighter wraps.
Stack a second clump the same size and bind it on the near side, starting it slightly toward you so any spin rolls it into place. Bind the butts with loose wraps, post it the same way, and check the two claws sit even. Snip any scruff.
Bind in the brown turkey or goose slip at the bend for the shellback, pointing rearward; it gets folded over later. Bury the excess.
Bind the brown hackle in by the tip a little way forward of the claws, not right back at them, so the legs do not run all the way to the crawdad's head.
Bind in the brown chenille and advance the thread to where the body will end. Take one big thick wrap of chenille behind the hackle, then wrap forward turn against turn. Seat with two wraps, snip, and lock with a couple more.
Palmer the hackle forward: open spirals at the rear, tighter as you reach the front. Seat with two or three wraps and snip.
Push the hackle fibres out to the sides, then draw the turkey slip forward over the top. Take a couple of loose wraps to check the position before locking it in, snip, and smooth out a small head.
Whip finish, then put a couple of big drops of UV resin on the shellback, spread it along the whole back and cure it. One coat is enough.