Why do caterpillars need to shed their skin when they grow bigger but not humans?

But we do! We shed skin cells constantly, regrowing at much the same rate so that it's not noticeable. Since our growth is not an overnight process, the replacement skin cells can generally keep pace. Which is good, because if we worked like caterpillars do, we'd have to stick kids in a new cocoon every six weeks or so when they hit their growth spurt.

But if sudden swelling takes place, say from an injury, it's quite common for the outermost layer of skin to flake or peal off, and a shiny pink new layer is exposed. So, in effect, we are shedding.