Molting

When a blue crab has grown sufficiently to require a larger shell, the following events occur:

Precdysis (pre-molt or “peeler” stage) :


-Molting hormones are released.
-The hypodermis detaches from the existing hard shell. The hypodermis is a layer of cells -directly beneath the shell.
-The hypodermis produces enzymes which begin to dissolve the shell components. Much of the existing shell is recycled causing it to become thin. Inorganic salts are resorbed from the shell and stored internally.
-A new inner soft shell slowly forms underneath the existing shell. When this new shell has fully formed, the crab will be ready to molt.

Ecdysis (molting or “busting” stage):


-The crab stops eating and seeks shelter in order to avoid predation. During this process the crab is highly vulnerable to predators, including the two-legged variety!
-The crab rapidly absorbs water which causes its tissues to swell and split the old shell open across the back between the lateral spines. Fracture planes in the claws split open to allow the claws to be pulled through.
-The crab begins the slow, arduous process of backing out of its old shell, which is then discarded.
-The newly molted crab pumps water into its tissues in order to inflate the shell to its new size.
-The new shell will be roughly one-third larger (33%) than the old shell. The new shell reaches its full size within six hours after molting.

Postecdysis (postmolt or “soft shell” stage):


-The salvaged inorganic salts are rapidly redeposited to help thicken and harden the new shell. -The new shell will only harden in water (the hardening process stops if the crab is removed from the water) and will take approximately two to four days to fully harden.
Over time, as the crab slowly grows inside its new shell, tissue water is replaced with protein. Once there is no more room left to grow inside this shell, the whole molting process starts over again.