The lobster’s shell is a rigid, non-living exoskeleton that limits the animal’s growth. Because this hard outer casing cannot expand, the lobster must periodically discard this restrictive structure to increase in size. This process, called molting, temporarily reveals the new, soft layer beneath, radically changing the lobster’s appearance and function.
The Exoskeleton and Molting
The rigid shell is primarily composed of a biocomposite material, a mix of organic matrix and calcium carbonate minerals. Since the exoskeleton does not stretch, a lobster grows incrementally by shedding the old shell, a process known as molting or ecdysis. Hormones regulate this mechanism, triggering the formation of a new, larger, but still soft shell underneath the existing hard one.
To escape its old casing, the lobster absorbs a large amount of seawater, swelling its body and creating hydrostatic pressure. This pressure causes the shell to split along a pre-formed line between the carapace and the tail. The lobster then carefully extracts its entire body, including its appendages and the linings of its stomach and anus, through the split in a process that can take about 30 minutes. This cyclical shedding also allows the lobster to regenerate lost limbs and repair shell damage.
Appearance of the Soft-Shell Lobster
Immediately after molting, the lobster has an entirely different texture and coloration than its hard-shelled counterpart. The newly exposed shell is extremely pliable, often described as feeling like soft leather, rubber, or gelatin, rather than hard armor. This new, flexible exoskeleton is paper-thin and noticeably larger than the body mass it contains.
The lobster achieves its increased size immediately post-molt by rapidly absorbing water, which inflates the new shell and expands its volume, sometimes by as much as 20%. This deliberate water absorption allows the lobster room to grow into the new shell before it hardens. The color of the soft-shell lobster is paler and duller than the mature, hard shell. It may appear washed-out, pinkish, or a less intense shade of its normal color, sometimes having a slightly wrinkled or baggy appearance due to the expansion.
Immediate Vulnerability and Behavior
Lacking protective armor, the soft-shell lobster is extremely vulnerable, which dictates its immediate behavior. The paper-thin shell offers little defense against predators like large fish, seals, and crabs, or against physical damage from rocks or strong currents. During this fragile period, the lobster’s most effective defense is hiding.
The lobster seeks immediate refuge in burrows, crevices, or under rocks until its new shell gains strength. The lack of a rigid structure also compromises the function of its claws, making them ineffective for fighting or defense without skeletal support. Furthermore, the soft shell is susceptible to penetration by microorganisms, increasing the risk of infection.
The Hardening Process
The soft-shell state is temporary, as the new exoskeleton begins to solidify almost immediately. The lobster begins the hardening process, called calcification, by absorbing minerals from the surrounding seawater and its own internal reserves. Calcium is the primary mineral required, and the lobster may even consume its discarded shell to quickly replenish lost calcium.
The time it takes for the shell to reach full rigidity varies significantly based on the lobster’s size, age, and water temperature. In warm water, the shell may begin to feel firm within two days. However, the transition to a fully hardened, thick shell can take anywhere from two to eight weeks. Once fully calcified, the lobster returns to its normal, protected state, ready for the next molt.