It’s that time of year again.
Empty crab shells littering the beach are often mistaken for dead crabs.
As part of their growth process, crabs actually shed their old shells as they grow new ones.
Walking along the tide-line you may occasionally notice numerous crab shells on the beach. Many people mistake these empty shells for dead crabs. What most people do not know is that as crabs grow, they shed their shells and grow new ones in a process called molting.
Discarded crab shells settle on the ocean floor until strong currents wash them ashore. Molted crab shells have all the external parts intact — including legs, antennae, eyes, and gill supports, which makes it difficult to tell whether or not you are looking at a dead crab or just a molt.
Molting begins with a secretion of hormones from the female crab, after which both female and male crabs fast. Surviving off their fat reserves, a crab will absorb as much calcium from its shell as possible — which aids in the development of the crab’s new shell. When the crab is ready to evacuate its old shell, a fracture opens along the underside of the back and the crab literally backs out of its shell.
The crab’s new shell (which was developing while the crab was fasting) is soft and flexible. The crab expands its new shell by filling its body cavity with water. During this time, the crab is extremely vulnerable to predators and will bury itself in the sand to avoid detection.
Once the crab’s shell starts to harden — which can take several days — the crab will resume feeding. Soon the crab will consume enough food to restore its fat reserves and replace the excess water in its shell with muscle. Then the cycle starts all over again!