Consensus of Martyn White and The Angling Company Key West
Materials
Body McFly foam (tan main; brown accent; or olive/white)
Weight Lead dumbbell eyes
Eyes Epoxy/mono crab (stalk) eyes
Legs Square rubber legs
Glue Contact cement (Pliobond) / super glue
How to tie it
Mount a lead dumbbell on the hook and turn the hook upside down.
Take clumps of McFly foam, tan as the main colour with a few strands of brown mixed in, and stretch them to about pencil-and-a-half thick.
Tie each bunch on with a figure-eight, lift, and take locking wraps; repeat with more bunches working forward along the hook.
Whip finish and trim the foam to a crab shape (round or oval), leaving it slightly large.
Singe the edges with a flame, being careful with the foam, to seal the shape and darken it slightly.
Cut the crab eyes' stalks to about half the body width, sharpen them, and stab them into the foam.
Coat the whole underside with contact cement and press the legs on: two single square rubber legs parallel to the shank and a front pair together for the claws.
Add a second coat of glue, tie knots in the legs, trim the claws short, and leave the other legs long.