I agree with Rip too. I've watched bass chasing crayfish & they're cautious about those claws. Sometimes to the point of giving up rather than get pinched. A big LM bass can certainly eat a big crayfish, but I believe when they have choices, they'll go after those that are easier to deal with.
I go with patterns that are non-descript when I know there are a good number of crayfish where I'm fishing. I used to tie patterns that looked like the crays, with segmented bodies & claws, but didn't really catch any more fish on them & they were time consuming to tie. I don't think there's anything wrong with that type of fly, but they're simply not necessary if you wish to imitate crayfish.
I like this type of Clouser style pattern for scooting along the bottom.
I had recently posted this fly & some others that I had tied for Redfish & bass.
I would use this type fly too as a crayfish imitation. I used this particular fly last week looking for bass, and in the water it looked very much like a crayfish. Notice, it only has the single rabbit strip tail. Bass can't count. Trying to add 2 claws to a crayfish pattern is fine, but I've yet to find it makes any difference.
Otherwise, I'll tie up patterns such as a Squimp, a saltwater pattern, in appropriate colors for a crayfish & use them. Many of the "Bonefish, Flats, or Redfish" style patterns that generally are intended to imitate shrimp, also make great crayfish imitations.
I believe I've mentioned this before, but once had a day on a small trout stream where I caught a brown, rainbow, SM bass & LM bass all on the same Stonefly nymph pattern. There were a lot of crickets in the grass & weeds along the banks, and there was a lot of small crayfish in the stream, that appeared to range in size from about a nickel to 3". I have no idea what those fish thought that fly was, but it didn't really matter.
This is the fly I used that day tied on a size 6 hook.
Frankly, I would rather try a fly that might imitate a crayfish or could be mistaken for other prey that the fish will eat than attempt to stick to a pattern that might only imitate a cray. (Not that it's likely it will anyway.)
I would bet that the Sculpin patterns that Ard has posted recently would work as well as anything.
