The large, green caterpillar known as the hornworm is the highly destructive larval stage of the Sphinx moth (family Sphingidae), also called the Hawk moth. These voracious garden pests undergo a complete metamorphosis to become large, fast-flying insects. The adult moths are sleek, powerful fliers that play an important ecological role as specialized pollinators.
Identifying the Hornworm Larva
The hornworm larva is the creature most people recognize, reaching up to four inches at maturity. Its body is typically bright green, providing camouflage among the foliage of its host plants. The defining characteristic is the stiff, pointed protrusion, or “horn,” located on its posterior end, which gives the insect its common name.
The two most common species are the tobacco hornworm (Manduca sexta) and the tomato hornworm (Manduca quinquemaculata). Both are significant agricultural pests because they feed almost exclusively on plants in the nightshade family (Solanaceae), including tomato, pepper, eggplant, and tobacco. The tobacco hornworm features seven diagonal white stripes and a reddish horn. Conversely, the tomato hornworm has eight V-shaped markings and a black or blue-black horn.
The Transformation Stage (Pupation)
Once fully grown, the larva ceases feeding and begins searching for a suitable location for transformation. The caterpillar burrows several inches deep into the soil, creating a small, earthen chamber for the pupal stage. The pupa is a hard, protective case where the reorganization from larva to moth occurs.
The pupa is a large, reddish-brown, elongated oval structure, typically around two inches long. A unique feature is a distinct loop or projection at one end, sometimes called a “jug handle,” which is the developing casing for the adult moth’s long proboscis. The pupal stage lasts two to four weeks during summer but often extends through winter, allowing the insect to overwinter until spring.
The Adult Form: Sphinx Moths
The final stage is the emergence of the adult moth, often called a Hawk moth due to its powerful flight capabilities. These moths have robust, streamlined bodies and long, narrow wings, making them some of the fastest-flying insects, capable of speeds exceeding 30 miles per hour. They are primarily nocturnal or crepuscular, active during the twilight hours of dawn and dusk.
The adult moths are generally mottled gray and brown, providing camouflage while they rest during the day. Their abdomens feature distinctive markings, such as the five pairs of yellow or orange spots on the Five-spotted Hawk Moth (tomato hornworm adult) or six pairs on the Carolina Sphinx Moth (tobacco hornworm adult). These spots are revealed in flight and act as a warning display to potential predators.
Adult Sphinx moths are important pollinators, frequently mistaken for hummingbirds because they hover in mid-air while feeding. They use their exceptionally long, coiled proboscis to reach nectar deep inside flowers without landing. This specialized feeding habit links them to plants with long floral tubes. Unlike the larvae, the adults focus on reproduction, completing the cycle by laying eggs on the underside of host plant leaves.