Life Below - The Crab

With their exoskeletons, crabs may seem fearless ! But this special creature, as tough and hard-shelled as a crab may seem, is in fact vulnerable a lot of its life.
Photo by Alex Braga

On the sand floor, a liveless crab shell drifts around… But the crab isn't dead, - its hiding elsewhere.

Under some big bulks of rocks not far from the shedded shell, the crab is found. At a glance it dose not look any different, but the first appearance leves You fooled. The crab, who would usually be waltzing around on the open ocean floor protected by an armor, is at this point soft and therefore extremely vulnerable !

The crab is in the special process of “molting”.


“Molting” is the periodical process when the crab is growing.

Just like snakes and other reptiles sheds their skin when they grow, - crabs need to shed their exoskeleton in order to grow…

But there is a major difference. When a snake grows, - it can be compared to when we, humans, get a rather rough sunburn, and our skin peals off… We still have new skin underneath to protect us. Crabs, on the other hand, need time to harden their shell before they are safe and protected once again. And this takes time.

There are many steps in the molting process…


Step One: Preparing the Molting process.

When it is about time for a crab to molt, - it starts the preparations…

The Crab will absorb Calcium into its blood and at the same time, the crab releases an enzyme that breaks down the old shell and connection to tissue layers as well as the muscles underneath the shell. By the end of this phase, the crab creates an extremely thin and flexible new shell layer underneath the old shell.


Step Two: Crab goes wannabe Pufferfish.

The day before the molting will start for real, the crab begins taking in water, and filling its body up entirely… Just like a pufferfish trying to scare off predatores, - or like Donald Duck pumping his air madress to the point where it almost explodes. And this is also the point ! When the crab takes in water, the crabs tissue expands, which helps the crab to loosen and break the old shell.

At some point, the old shell cracks open, and it is now possible for the crab to continue on to the next step of its molting process…


Step Three: What was the middle thing ?

Here comes the tricky part of the process… The crab needs to remove the old shell with its now soft and flexible new shell layer. Due to this troubling mixture, it can take many hours, before the crab has rid itself of the old shell.


Step Four: Vulnerability.

All of a sudden, the crab tranforms from an armored predator, to a fragile and vulnerable animal. Many predators would be thrilled to come across this soft, delicate being ! So the crab needs to hide itself well.

Before the full shell is properly hardened, days and sometimes even weeks can pass, - depending on the crab specie as well as its age. Meanwhile the hardening process takes place, the crab continues to pump its body up with water, in order to make space for itself to grow, - and in order to make sure as long time as possible will pass before a new molting will take place.

The crab stays hidden all meanwhile the shell is hardening.


Step Five: Finishing up.

At some point, the hardening is finishing up, - and the crab is now ready to leave its safezone.

Now, the crab has a tuned armor and has increased its size with 25% - 40%.

But that is not all !

Photo by Darrell Cassell

The molting process is not only essential to the crabs growth, it is also rids the crab of parasites such as barnacles and tube worms ! And if the prior shell had been damaged in any way, the molting also patches this up. That is also the case, concerning missing legs or claws. They will be regrown, bit by bit,

every time a crab molts.


For some crab species, the molting periodical process is also the time to create a new generation of crabs.

Just like when a couple takes off their clothes to make love the, for instance, Dungeness Crabs removes their hard exoskeletons, since they need to be soft bodied, in order to mate.


The molting process is an important affair.

This rather long process, may seem like a once in a lifetime happening, - but actually, molting occurs frequently for Crabs. Depending on their specie and age, molting can occur several times annually.


“As untouchable this armored predator may seem, it is in fact extremely vulnerable a lot of its life.”