How do you tell a male hermit crab from a female hermit crab? Well there are some people with theories out there. Theories about claw size, and theories about color, and theories about certain hairs on certain sections of the body but they are all just theories. Right now we really have no idea how to tell a male hermit crab from a female hermit crab. It is one of the collective mysteries about these little creatures that is so interesting and so comical. Really we understand a very little bit about how they breed in the wild. We understand very little about their genders. My guess is in the long run really probably the only way to tell them would be a lot like telling with tarantulas and using their molted skins under microscopes but seeing how it is virtually impossible to get hermit crab molts out of the substrate as least as far as I know chances are we will probably not in the near future know how to sex hermit crabs but you never know, you may be the one to figure it out.