Molting is the process where crabs shed their rigid outer shell (exoskeleton) to allow their bodies to increase in size. This process is necessary because crabs, like other crustaceans, cannot grow in a linear fashion like most animals due to their hard outer shell that does not grow. Instead, they must shed their shells, a process called molting. Prior to molting, a crab reabsorbs some of the calcium carbonate from the old exoskeleton, then secretes enzymes to separate the old shell from the underlying skin (or epidermis). A day before molting, the crab starts to absorb seawater, and begins to swell up like a balloon. This helps to expand the old shell and causes it to come apart at a special seam that runs around the body. The carapace then opens up like a lid, and the crab extracts itself from its old shell by pushing and compressing all of its appendages repeatedly. First, it backs out, then pulls out its hind legs, then its front legs, and finally comes completely out of the old shell. This process takes about 15 minutes. When a crab molts, it removes all its legs, its eyestalks, its antennae, all its mouthparts, and its gills. It leaves behind the old shell, the esophagus, its entire stomach lining, and even the last half inch of its intestine. After molting, the new shell is very soft at first, making the crab vulnerable to predators. Within a few days, the shell hardens up, and it becomes very hard after a month.

Crabs molt regularly throughout their lives, and the result of each molt is typically a 25%-40% increase in carapace width. When crabs molt, they leave their gills and eye sockets, making them appear more like dead crabs than molts. However, Crab Team monitors look at hundreds or thousands of molts over the season and get very good at telling the difference between a molt and a dead crab.