The answer to this question is, in fact, very interesting. Hornworms are the larvae of hawk moth. They can be found in North America and they feed on plants such as corn and tobacco. In order to turn into a full-grown moth, the hornworm goes through four stages of development: egg, larva (hornworm), pupa (chrysalis), and adult moth.
As larvae, these are considered a great animal feed and are farmed for such. As a moth (and in the wild in general) these are considered a nasty pest that destroys crops.