Taking time this winter to revise some of my fly designs. Here's gen. II of the Sipsey Claw Craw which is my version of the red swamp crawfish.
Bucktail: natural, brown or red
#2 main hook
#4 stinger hook
gold bead chain for eyes
50 lbs mono for the stinger hook
brown yarn for body
3mm rattle for the underbody
Red bucktail would work. The brown portion of the bucktail would have a red tint, thus more accurately matching the raw swamp crawfish's color pattern.