Thread Chartreuse or fluorescent green 210 denier UTC
Materials
Lead dumbbell eyes Plain or painted (One pair, medium)
Krystal Flash One strand black, one strand root beer (Both doubled over for antennae)
Craft fur Tan craft fur (One clump for the mouthparts, plus more for the dubbing loop body)
Chinese neck hackle tips Furnace or cree chinese neck hackle tips (Two, for the claws)
Rubber legs Natural latex, barred with markers (Three pairs)
Hard mono Clear weed guard (12 lb Mason, one length for the weedguard)
Permanent marker Black ostrich herl (For drawing the eyes)
How to tie it
Mount the 811S and lay a base of 210 denier chartreuse thread. Tie the medium lead eyes on top of the shank about two eye lengths behind the hook eye with tight figure-eight wraps so the fly rides hook point up.
Tie in a length of 12 lb hard mono at the eye position and leave it pointing forward out of the way; it becomes the weedguard at the end.
Run the thread back to the bend. Double one strand of black and one strand of root beer Krystal Flash over the thread and tie them in at the bend as antennae, splayed slightly.
Stack a small clump of tan craft fur and tie it in at the bend, extending back over the antennae, as the mouthparts.
Tie one furnace or cree hackle tip on each side of the shank at the bend, curving outward, to form the claws; keep them splayed rather than stacked so the crab shows a wide profile.
Bar three pairs of natural latex rubber legs with markers and tie them in on the sides of the shank, one pair at the bend and the others spaced forward along the rear half, so they stand out to the sides.
Form a long dubbing loop, load it with tan craft fur cut from the hide and spun so the fibers stand out evenly, and spin it tight into a brush.
Wrap the craft fur brush forward over the shank, stroking the fibers rearward between turns, working around and through the leg tie-in points and up to and around the lead eyes. Tie off behind the hook eye.
Trim the spun craft fur to a flat, oval crab-shell shape, thin at the edges and fuller in the middle, keeping the legs and claws clear of the scissors.
Bring the hard mono back under the hook eye, bend it into a loop clearing the hook point and tie it down to form the weedguard, then trim.
Build a small head, whip finish, cement, and draw the crab's eyes on the flattened body with a black permanent marker.