Understanding Evolution

Molting and the exoskeleton: Squishy crabs

What would the molting process be like for a small terrestrial arthropod versus a large one? Imagine each of them wriggling out of their old exoskeletons, and emerging with their new exoskeletons still squishy and weak.

To jump-start your imagination, here's a virtual experiment. You're going to fill two different balloons with water. The balloons are different sizes but are made of the same rubber. Click on the faucet above each of them to fill the balloon and see what happens when it is set on the ground. Which balloon deforms the most?

Quivery crabs

Before its new exoskeleton hardens, a newly molted arthropod is a bit like a water-filled balloon — a delicate membrane holding in a liquid filling. What do you think will happen to the body of each crab below once it molts and no longer has the support of an exoskeleton? Click on the small and large crabs to see how each holds up.

Is the physics of molting a constraint on arthropod size?


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