Being able to tell your male crabs from your female crabs can come in handy. The difficulty of determining the gender of a crab can range from quite easy to moderately challenging, depending on the type of crabs you are trying to sex. The larger the crab is, the easier it is to determine the gender. Handle your pet crab gently and try not to unnecessarily stress him out as you determine his gender. Also be sure to avoid getting pinched by his claws.
Look at the crab's claws. In some species of crabs, like the fiddler crab, males will have one claw that is significantly larger than the other. If you are trying to tell the gender of blue crabs by their claws, then it is fairly easy. Blue crab males have blue claws while the females have red-tipped claws.
Pick up your crab from the rear and gently turn him over. Do not shake him or pull on his legs. Avoid his claws.
Look at the underside of your crab. If "he" is in fact a he, then you will notice a triangular shape on the rear section of the bottom of his underside. If "he" turns out to be a she, then you will notice a broad, round marking in the same area that does not have such a triangular appearance.
- In the case of hermit crabs, you may have difficulty telling the gender because many hermit crabs will not come far enough out of the shell for you to identify gender markings. Pulling a hermit crab out of its shell forcefully may seriously harm or even kill it, so don't do it. Female hermit crabs have two small spots called gonopores that will be visible when you look at the top of your hermit crab's back walking legs.
- You can secure the claws of larger crabs with rubber bands before you turn them over to tell the gender, but securing the claws may take more time and effort than it does to just catch a glimpse of their undersides.
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