When a lobster moults, a process known as ecdysis, the individual undergoes many physiological and behavioural changes. Behaviourally there will be an increase in activity and movement, as well as building shelters and barricading entrances.
Physiologically, before ecdysis, the lobster lays down a new exoskeleton which is complete in every detail, including the start of any limbs that have been lost. Minerals are removed from the old exoskeleton, blood is removed from the claws and other limbs which causes them to shrivel, and the lime in the joints of these appendages dissolves. Just prior to ecdysis the lobster absorbs water causing the new exoskeleton to swell, pushing apart the old exoskeleton. The lobster then withdraws all its shrivelled limbs from the old exoskeleton.
It takes anything from several minutes to over half an hour to escape from the old carapace. The stored minerals are then redeposited into the new exoskeleton and the lobster resumes water uptake, transferring the water to its blood and body tissue. It takes a couple of days for the new exoskeleton to harden, however an adult won’t be fully hardened for several months. Between moulting the lobster adds tissue in place of the water it absorbed, effectively growing into its new carapace.
A lobster will normally eat the moulted carapace to reuse the lost calcium, it is therefore important that in a captive environment the moult is not removed straight away. We always leave the carapace in the tank for a couple of days for our lobsters to consume. In this photo the lobster did not consume the carapace, but spent several days burying it. We can assume his diet is sufficient enough that he didn’t need to reconsume the calcium, instead he wanted to cover up any evidence that he is in a soft delicate state. It also acts as some great enrichment; he spent every minute of 3 days attending to the carapace.