Hermit crabs are considered arthropods. This means that the body of a hermit crab is segmented and the legs are jointed. The body of a hermit crab has three regions: the head, thorax and abdomen. Determining the sex of a hermit crab can be difficult, as true sexing of a hermit crab requires the crab to willingly leave his shell. There are a few possible ways to tell the sex of your hermit crab without causing unnecessary harm.
Hermit crabs usually have ten legs. These legs include claws, grooming legs and walking legs. A male hermit crab will have tufts of hair that can be located at the bottom of his 5th pair of legs.
The female hermit crab contains small openings known as gonopores. According to The Hermit Crab Patch, a female hermit crab's gonopores can be found directly on the top segment of the female's 3rd pair of walking legs. The gonopores can be relatively small to see, and using a magnifying glass can help you discern the genital openings. If you can manage to identify gonopores, then you have a female hermit crab.
A male hermit crab won't have any appendages on his abdomen. A female hermit crab will have three feathery looking appendages only on the left side of her body. These feathery appendages allow the female to hold eggs securely prior to their release.
According to the Sea Shell Shop, you cannot tell the difference in sex with hermit crabs by claw size. The difference in hermit crab species means differences in claw size and color variation of the claws. The size of a hermit crab's claw will only help identify the species of the hermit crab.
A hermit crab is reluctant to leave his shell unless he's molting or moving into a new shell. Even if you're itching to know the sex of your crab, it's important to not force your crab to come out of his shell. Forcibly removing your crab can cause severe injury (the ripping of the abdomen) and the death of your crab.