Growth via molting generally works like this:
- Inside its exoskeleton, the arthropod grows.
- When the exoskeleton finally gets too tight, the animal begins the molting process by puffing itself up and splitting the exoskeleton.
- The new exoskeleton is still soft, so the arthropod wriggles out of the old armor very carefully to avoid damaging its still-vulnerable body.
- Then, the arthropod waits — sometimes for days — without protection or body support for its new armor to harden before life as usual begins again.
These images, in sequence from 1 to 5, show a blue crab molting. The crab emerges from its old exoskeleton significantly larger than it had been.
Crab molting photos provided by the Smithsonian Environmental Research Center and Alicia Young-Williams