Hornworms are common garden pests known for their voracious appetites, particularly for plants in the nightshade family. These caterpillars can rapidly defoliate host plants, causing significant damage. Understanding their appearance at various life stages helps gardeners and growers identify and manage them. While often associated with tomatoes, hornworms have a life cycle including egg, larval (caterpillar), pupal, and adult moth stages, each with distinct visual characteristics.
Identifying the Hornworm Caterpillar
The larval stage, commonly known as the hornworm caterpillar, is the most recognized form due to its size and feeding habits. Hornworm caterpillars are large, cylindrical, and plump, reaching lengths of up to 4 inches (10 cm) at maturity. Their bodies are typically bright green, which provides effective camouflage among plant foliage. They possess five pairs of prolegs, which are fleshy abdominal limbs that aid in gripping plants.
Two primary species, the tobacco hornworm (Manduca sexta) and the tomato hornworm (Manduca quinquemaculata), share similar appearances but have distinguishing features. Tobacco hornworms feature seven diagonal white stripes along each side of their body, often bordered with black, and a red or orange-red horn at their posterior end. In contrast, tomato hornworms display eight V-shaped white markings on each side, lacking the black border, and possess a black or bluish-black horn. Both species also have small black dots, called spiracles, along their bodies. Their presence is often first indicated by dark green or black droppings on leaves or the ground.
Appearance of Other Life Stages
The pupa is a dark brown, rigid, oval-shaped case, typically measuring about 2 to 3 inches (5-7.6 cm) long. A distinctive feature of the hornworm pupa is a “jug handle” or “maxillary loop,” which is a curved projection containing the developing mouthparts of the adult moth. This stage is generally inactive and occurs underground.
The adult form of the hornworm is a large sphinx moth, also known as a hawkmoth. These moths have narrow forewings and a wingspan that can range from 3 to 5 inches (7.6-12.7 cm). Their coloration is typically mottled gray and brown, resembling tree bark, which aids in camouflage. Both species have distinct abdominal spots; the five-spotted hawkmoth (adult tomato hornworm) usually has five pairs of yellow or orange spots along its abdomen, while the Carolina sphinx moth (adult tobacco hornworm) typically has six pairs of these spots. These moths are nocturnal and possess long, coiled mouthparts used for nectar feeding.
Where to Find Hornworms
Hornworms are primarily found on plants belonging to the Solanaceae family, which includes common garden crops like tomatoes, peppers, potatoes, and eggplants. Tobacco is also a preferred host plant for the tobacco hornworm.
They tend to feed on the upper parts of plants, consuming leaves and sometimes fruit. While they can be present throughout the growing season, populations typically peak in mid-summer. Hornworms often remain near the main stem of the plant during the day, becoming more active and moving to outer portions of the plant during dusk and dawn. The pupae typically overwinter in the soil, burrowing about 4 to 6 inches deep.