Lay a base of black thread back to the start of the bend.
Wax the thread. Pull a small patch of muskrat and pluck out the longest guard hairs, leaving some brown in the mix, then roll it in your palm into a ball of dubbing.
Touch-dub the muskrat on thin and wrap the body forward with a taper, thinner at the back and thicker up front. On a 1x long hook it takes two or three applications; add dubbing as needed. A little fuzz is fine, it gets brushed out later.
Take a small clump of gray squirrel tail from the side of the tail for the wide tips and stack it; squirrel is slippery and stacks well. Pull out about a quarter of the bunch. The wing should reach the back of the body, not all the way to the bend.
Switch hands and catch the wing on with a pinch wrap and a couple more wraps, holding the rear of the clump tight with your material hand so it does not spin. Add a few more wraps, then lift the butts and snip them as close as you can to leave room for the head.
Take the thread to the eye and build a decent-sized nymph head, then a four-turn whip finish and head cement.
Rough up the fur on the underside with a dubbing brush or toothbrush so it sweeps back and gets that wiggly, lifelike movement.