A caterpillar is a type of insect.
In 2151, Doctor Phlox fed a deceased caterpillar to one of the animals in his sickbay aboard Enterprise NX-01. Having done so before, he asked the animal he was feeding not to bite his fingers this time. Once he had fed the animal without getting his fingers bitten, Phlox, pleased with the outcome, took a second dead caterpillar and ate it himself. (ENT: "Dear Doctor")