How and why do lobsters shed their shell?

Did you know that in order for a lobster to grow, it must shed its shell – this is a process called moulting.

Lobsters begin this process when they hatch – check out this little one going through its third moult at just two weeks old.

Every time a lobster moults, it offers it the chance to ‘regenerate’ its body – this means, if it’s lost legs or claws in the past – it can regrow them! The photos below show a ‘before’ and ‘after’ of a moult!

Before the moult... 4 legs, no claws and no antennae!

After Moulting, believe it or not, this is the SAME lobster - antennae, new claws, and all her legs have returned! Incredible!

Graphic by Lobster Conservancy

So now we know why lobsters moult – but how exactly do they do it?

Before moulting, a fully formed new shell (exoskeleton) is produced underneath the existing shell. Nutrients from the old shell are drawn back into the body and water is brought in, swelling the outer shell so much it splits. Once split (on the back where the carapace meets the tail) the lobster will draw it’s whole body out of the old shell, revealing the perfectly formed new exoskeleton. At first this new shell is soft, over the next few days it will harden up to create a protective layer.

Female lobsters will use this time immediately after moulting to mate. They are vulnerable before their new shell hardens up and the male they mate with will protect them from predators during this time. If a lobster has lost limbs (they can amputate their own limbs to escape danger or lose them in fights) they can regrow them when they moult!

Did you know?

A great way to speed up the hardening of the new shell is to eat their old shell! Sounds pretty gross but that shell is full of important nutrients like calcium and this can really help to strengthen the lobster!