It's illegal to keep female crabs (dungoness anyway). They have that pull tab looking thing on the bottom of them, the females is wide and the males is narrow.

Doug

crabs
 

If you'd like to rid yourself of them I'm more than happy to take them.My mantis loves crabs.I could pick them up as well.LMK.Clint

actually its only illegal for commercial fishermen to keep females, i think most people put the females back regardless.

Richard

I had a look at the hitchhiker crab videos I've made over the past year. Three videos of them show the undersides of the crabs in some detail. They all look like they could be female, though they do not look exactly like the female shown in the photo link. I'd venture to say that the crabs we find in our tanks are very young and they may not be showing their male/female traits at such an early age.

See if you can tell me for sure if these are females...

Crab One

Crab Two

Crab Three