A hornworm is a green caterpillar with a pointed, sharp tail. The tomato hornworm has V-shaped white stripes on its body and a black "horn," and a tobacco hornworm has diagonal white stripes and a red "horn."
Unchecked, hornworms are destructive to tomato, eggplant, pepper and potato plants. Their green color helps them blend in well with the plant leaves. They can quickly defoliate a plant, and it is not unusual to notice the destruction and waste droppings before discovering the hornworm itself. The easiest way to control hornworms is to handpick them from the plants and destroy them, says Colleen Vanderlinden, expert for About.com Organic Gardening.