Crawfish are just like people: each one is unique and different from the rest. Genetics can play a role in their pigmentation, too. But late in the season, many crawfish are darker simply because they are older and have reached maturity. They are at “full size” and don’t need to molt out of their shells any longer. So they appear darker, and their shells become harder and can sometimes be tougher to peel.
Question & Answer: Why are some of the crawfish so dark?