Life Cycle of the Blue Crab - The Molting Process

Text says, The Blue Crab

a photo of a crab and the molting process

The Molting Process

How do crabs grow?

The rigid shell imprisons the crab and limits growth.

Crabs grow by shedding their outgrown shell.

Once the shell is shed, the crab can absorb water and expand into its new-grown shell.

	Having reached the "buster" molt stage, a Maryland blue crab, Callinectes sapidus, sheds its shell. During its lifetime a crab may molt 20 to 25 times, increasing its size as much as 1/4 to 1/3 each time.
	Photos Courtesy of Mary Hollinger, NODC biologist, NOAA - America's Coastlines Collection

How much does a blue crab increase in size on molting?

illustration depicting growth of crab by about one-third for 3 successive molts

Under normal conditions, the Blue Crab increases about one-third it's size with each molt.

What is the difference between soft and hard shell crabs?

They are the same species.

A soft-shell crab is a crab that has just discarded its shell.

Immediately after the molt, when the old hard shell has been shed, the crab's new shell is pliable and easily stretched. Now the crab is called a "soft crab" or a "soft shell crab".

Large amounts of water are consumed prior to and shortly after the molt, causing the soft shell to expand and increase in size. This entire process takes 2-3 hours and within 2 hours after the shed, the new shell begins to harden.

Crabs which have just shed their shell hide in rocks or bury themselves in sand and mud to escape predators.

The "papershell" is formed within 12 hours and an additional 2-3 days are needed before the shell fully hardens.

They come back out after the new shell hardens.