Answer:
Female hermit crabs have gonopores on their second set of walking legs, whereas male hermit crabs do not have gonopores at all. You can see pictures to illustrate this by clicking on the related link, below.
You may be able to see whether your hermit crab has gonopores during or after it's weekly bath. You could also try to see by gently placing the crab inside a clear glass bowl and, as the crab tries to climb the slippery surface, you may be able to view the second pair of walking legs.
However, many hermit crabs are reluctant to come far enough out of their shells for you to tell whether they have gonopores or not. Some may never let you see. You should not try holding the crab above a table and making it reach out as your crab can easily hurt itself by doing this.
You must be very patient and must never try to force them to come out of their shell. Pulling on the crab can seriously harm, or even kill, the crab because it will hold so tightly to the shell to try and protect itself that you could tear it apart.
Per #6 of WikiAnswers Copyright Violation and Plagiarism Policy cited from Crab Street Journal.com