With us humans, this phrase would usually mean we’d had quite a fright. Caterpillars, on the other hand, while not easily startled, jump out of their skin on more than one occasion. When they first hatch, they are still very small. As their mother has laid the eggs directly on her offspring’s favourite food plant, the little critters can start tucking in right away. Lacking any other interests, they do nothing but eat, gaining in both length and girth.