Two species can damage tomatoes. General color is green with white diagonal lines on its side. Prominent horn on rear gives name to the group. Larvae measure up to 4 inches long.
Damage is done by larvae eating foliage and sometimes fruit on eggplant, pepper, and tomato.
It passes the winter as a pupa, which gives rise to the hawk moth during late spring. Incubation period of eggs is about a week; larvae feed about 4 weeks. Pupal stage lasts about 3 weeks, except for the overwintering generation.
Source: The Entomology Department of Clemson University
Link: More information on hornworms and hummingbird moths from Colorado State University Cooperative Extension.