1. The sight of a crab while taking a stroll on the beach, foretell quarrel.
2. Thick crab’s shell is the signal of a cold winter
3. A crab will transform into a scorpion when buried in horse dung for three months.
4. Crab is the sign of ill nature
5. Scotch fisherman are not allowed to say “parten” (crab), or else, he will be cursed such that, lost of lines.
6. If a sailor had a crab clasping his foot, it symbolize shipwreck and drowning.
Source:
Crabs Folklore 