The hornworm is the common name for the large, destructive caterpillar stage of two sphinx moth species: the Tobacco Hornworm (Manduca sexta) and the Tomato Hornworm (Manduca quinquemaculata). These organisms undergo complete metamorphosis, inhabiting vastly different locations throughout their lives, from a feeding larva to a powerful, night-flying moth. Understanding where these two species reside at each stage is the first step in recognizing their presence and managing their populations.
Geographical Distribution Across North America
The distribution of these two hornworm species varies significantly across the continent, though their ranges overlap considerably in the central United States. The Tobacco Hornworm (Manduca sexta) is largely concentrated in the warmer, southern states, particularly along the Gulf Coast, but its established range extends northward to New York. This species is much more widespread globally, found throughout Central America, the Caribbean, and much of South America.
The Tomato Hornworm (Manduca quinquemaculata) tends to be the more prevalent species in the northern states and southern Canada. While found across the entire lower 48 states, it is less common in the Deep South than its relative. Both species cannot survive cold northern winters, so populations in these areas are often re-established annually by migrating adult moths flying north.
The adult moths, which are strong fliers, cover long distances, contributing to the annual re-colonization of northern territories. They overwinter as pupae buried in the soil. The percentage of individuals entering this long-term resting state, called diapause, increases as day length shortens in late summer. This strategy allows the species to persist in their core, warmer habitats while using the summer months to temporarily expand into colder regions.
Specific Habitats and Primary Host Plants
The micro-environments where hornworms are found are defined by the presence of their exclusive food source: plants belonging to the Solanaceae family. This family, commonly known as the nightshade family, contains potent chemical compounds the caterpillars have evolved to tolerate. Consequently, the primary habitats for the feeding larval stage are agricultural fields and home gardens where these plants are cultivated.
The specific host plants the larvae target include tomato, tobacco, potato, pepper, and eggplant. Once an adult female moth selects a suitable host plant, she lays her eggs directly onto the foliage, ensuring the newly hatched caterpillar has immediate access to food. The larvae remain on the plant, consuming large amounts of leaf tissue, meaning a single caterpillar can quickly defoliate a plant.
Although they prefer cultivated crops, hornworms also feed on various wild Solanum weeds, such as horsenettle. This reliance on a single plant family means that finding a hornworm is contingent upon finding one of these specific host plants in a garden or field setting. Their bright green coloration provides remarkable camouflage against the foliage, making them difficult to spot despite their large size, often reaching up to four inches long.
Location During Different Life Stages
The hornworm life cycle involves four distinct locations corresponding to the stages of complete metamorphosis. The cycle begins when a female sphinx moth lays her tiny, spherical, pale green eggs individually on the underside of a host plant’s leaves, a location that offers protection from predators and sun exposure. The egg stage lasts only a few days.
The larval stage, the hornworm itself, remains confined to the host plant for approximately three to four weeks, moving constantly to feed on leaves and occasionally boring into the fruit. Once the larva is fully grown, reaching its maximum size in the fifth instar, it leaves the host plant entirely. It drops to the soil directly beneath or near the plant where it spent its life feeding.
The pre-pupa burrows several inches deep into the soil, typically three to four inches below the surface, where it excavates a small chamber to transform into the pupa. This dark brown pupal stage is where the insect overwinters, remaining dormant until the following spring or summer. The pupa is recognizable by a distinctive handle-like projection that encases the adult moth’s developing mouthparts.
Finally, the adult sphinx moth emerges from the soil and takes flight, occupying an entirely different habitat. These large, robust moths are nocturnal, flying at dusk and night, often far away from the garden where they developed. The moths feed not on leaves, but on flower nectar, hovering like hummingbirds over deep-throated flowers to extract the sugary liquid using their long proboscis. They then restart the cycle by seeking out new host plants for egg-laying.