It's extremely difficult to tell the sex of your hermit crab. The only way to be certain if a hermit crab is male or female is to get a look under her shell. Wait until the hermit crab is most, or all, of the way out of her shell before attempting to determine her sex.
Locating the Gonopores
Female hermit crabs have tiny genitalia that become exposed when they’re most, or all, of the way out of their shells. You may be able to coax her out of the shell if she’s familiar with being handled. Do not attempt to force your hermit crab out of her shell, as this can seriously injure your pet. Instead, wait until she comes out on her own. Then inspect her body for genitalia, known as gonopores. They’re located on the back of her legs, closest to the abdomen and the joint of the cephalothorax. They will look like two tiny holes in her body. Male hermit crabs do not share this trait.
Determining a Female by her Eggs
You can instantly determine if a hermit crab is female if she’s carrying eggs. If you have both male and female hermit crabs, they will mate by partially leaving their shells, but only if they’re kept separately. Male and female hermit crabs that are kept together in captivity will not mate. The male deposits spermatophore into the female, thus fertilizing her eggs. The female will then carry the eggs on her body for a period of one month. If you notice a cluster of reddish brown eggs around your hermit crab’s body, she is definitely a female.
Determining a Male by his Body Hair
Although it’s not entirely conclusive, you can tell males by the amount of hair they have on their bodies. Females have very little hair on their bodies, compared to male hermit crabs. If he is covered in lots of tiny hairs, there’s a good chance he’s male. You can make this determination conclusive by coaxing him out of his shell and verifying that he doesn’t have gonopores.
The Luck of the Draw
Unfortunately, it’s extremely rare to be able to determine the sex of a hermit crab at the pet store. It’s also rare that pet store employees will know the sex of their hermit crabs. Oftentimes, they tell you it’s the “luck of the draw,” which isn't really helpful when you’re attempting to breed hermit crabs. Try to use the information you do know about hermit crab genders to make your selections, but don't be surprised if you end up with a male when you really wanted a female. Luckily, hermit crabs are an inexpensive, low-maintenance pet, so you can always add more.
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