Why is my crab up side down?

Crabs can flip themselves over by using their legs. They typically do this when they are molting or when they are injured. Molting is a process in which a crab sheds its old exoskeleton and grows a new one. Crabs are vulnerable while they are molting, so they often flip themselves over to protect their soft underside. If a crab is injured, it may also flip itself over to avoid further damage.

Sometimes, crabs will also flip themselves over for fun. They may do this to get a better view of their surroundings, or to play with other crabs.