ELI5 How do crabs and spiders get bigger after sheding their skin assuming there smaller then it when they start

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ELI5 How do crabs and spiders get bigger after sheding their skin assuming there smaller then it when they start

In: Biology

After they shed, their shell is very soft. They can inflate with air or water to puff up their bodies, and then the shell hardens in their new larger size.

Underneath the hard shell they shed is a new shell, soft, and crumped/shrunk a bit. Once the old shell is off the new shell rapidly expands and hardens. The now larger but partly empty crab grows to fill its new home, then does it again.