Caterpillar feeding on Hydrangea bush

Have you ever been outraged by discovering a prized plant chewed up by caterpillars or some other insects? Well  this one and his siblings defoliated an entire Hydrangea bush in the garden. It seems to be natures rule that this specie of caterpillar feed only on Hydrangea leaves. The Hydrangea plant does not seem to mind for a week or two later new leaves burst out from every node of the naked branches.