Hornworms, often recognized as garden pests, undergo complete metamorphosis. This process involves distinct stages, leading to an adult form surprisingly different from the caterpillar.
Understanding the Hornworm (Larva Stage)
Hornworms are the larval stage of specific moth species, commonly found feeding on plants in the nightshade family, which includes tomatoes, tobacco, potatoes, and peppers. These caterpillars are large, reaching up to 4 inches long when mature, with a cylindrical body and a prominent horn-like projection at their rear. Their green coloration helps them blend seamlessly with plant foliage, making them difficult to spot despite their size.
Two common types are the Tomato Hornworm (Manduca quinquemaculata) and the Tobacco Hornworm (Manduca sexta). Though similar, they have distinguishing features. The Tomato Hornworm has eight white V-shaped markings and a dark blue or black horn. The Tobacco Hornworm features seven diagonal white stripes, often with black margins, and a red or orange-red horn.
The Metamorphosis Process
Once a hornworm larva reaches its full size, typically around 3 to 4 inches long, it prepares for the next life cycle stage. The mature caterpillar ceases feeding and burrows into the soil, usually 4 to 6 inches deep, to pupate. This marks the beginning of the pupal stage.
The pupa is a hard, reddish-brown case, often elongated and oval, measuring about 2 to 3 inches in length. A distinctive feature is the “jug handle” or maxillary loop, a curved sheath encasing the developing mouthparts of the future moth. The pupal stage can last a few weeks during warmer periods or several months if overwintering in the soil.
The Adult Moth
After transformation within the pupal case, the hornworm emerges as a large, sturdy moth. These adults are commonly known as Sphinx Moths or Hawk Moths (family Sphingidae). They are often mistaken for hummingbirds due to their rapid wingbeats and ability to hover while feeding.
The Tomato Hornworm transforms into the Five-spotted Hawk Moth (Manduca quinquemaculata), which has a wingspan of up to 5 inches, gray and brown coloration, and a distinctive row of five yellow spots along each side of its abdomen. The Tobacco Hornworm develops into the Carolina Sphinx Moth (Manduca sexta), also gray-brown with a wingspan of up to 4 inches, and six yellow spots on each side of its abdomen.
Both adult moths are nocturnal, active at dusk and throughout the night. They feed on nectar from deep-throated flowers, using a long, coiled proboscis. As they feed, these moths inadvertently transfer pollen, playing a role as pollinators.