Soft-shelled crabs and hard-shelled crabs are of the same species. Blue crabs have a hard shell or exoskeleton. In order for the crab to grow, it must periodically shed its shell in a process called molting. Typically, a crab will seek shelter during this process because it is highly vulnerable to predators. The crab absorbs water, which causes the tissues to swell and split the shell in the back between the lateral spines. The crab then backs out of its old shell and discards it. It continues to pump water into its tissues causing a new shell that grows approximately 33% larger than its original size. The shell hardens again within 2 to 4 days. However, the shell will only harden in water; if the crab is removed from the water, the process is halted. To sell soft-shelled blue crabs, harvesters catch blue crabs just before the crabs are going to molt. The harvester can tell if a crab is in that "molt stage" by the color of the crab's exoskeleton in specific areas. Harvesters place the crabs in large shallow pans, watch them carefully, and take them out of the water soon after they molt.
