Hornworms are very large caterpillars (up to 5" long) that are the larvae of the sphinx (or hawk) moth, a large moth that is sometimes referred to as a Hummingbird moth because of their size and the way they fly. They are bright green with diagonal white stripes on their sides and a characteristic red or black horn at their back end. Tomato hornworms have a rather straight black horn and tobacco hornworms have a slightly curved reddish horn. Both are common pests in the vegetable garden.
Hornworms can be serious pests of tomatoes, peppers, potatoes, and even eggplants. They devour the leaves of these plants and because of their large size, they can defoliate a plant very quickly. Their camouflage coloring combined with the fact that they feed from the undersides of the leaves makes them very difficult to spot in the garden. Fortunately the large fecal pellets (frass) is quite easy to spot and this can help reveal their location.