Hornworms are large, green caterpillars often encountered in gardens, particularly among plants in the nightshade family. These voracious feeders can cause significant damage to foliage. These caterpillars undergo complete metamorphosis, emerging as distinct adult moths.
The Moths Revealed
Hornworms develop into large insects commonly known as Sphinx Moths or Hawk Moths, belonging to the family Sphingidae. The two most frequently encountered species are the Tobacco Hornworm (Manduca sexta) and the Tomato Hornworm (Manduca quinquemaculata). Both adult moths are robust, with wingspans ranging from 3.5 to 5 inches (9 to 13 cm). Their streamlined bodies and narrow wings allow for swift, agile flight.
These moths are primarily nocturnal, feeding on nectar from various flowers while hovering like hummingbirds, earning them the nickname “hummingbird moths”. The Five-spotted Hawkmoth (Manduca quinquemaculata), the adult form of the Tomato Hornworm, is distinguished by five pairs of yellow or orange spots along its abdomen. In contrast, the Carolina Sphinx Moth (Manduca sexta), which emerges from the Tobacco Hornworm, features six pairs of orange or yellow spots on its abdomen. Both species exhibit mottled gray and brown wing patterns, which provide effective camouflage.
The Hornworm Life Cycle
The life cycle of the hornworm involves a complete metamorphosis, progressing through four distinct stages: egg, larva, pupa, and adult. This transformation takes about 30 days under optimal conditions, though it can extend longer in cooler temperatures. The cycle begins when female moths lay small, spherical, translucent green eggs, usually on the underside of host plant leaves. These eggs hatch within three to five days.
Upon hatching, the tiny larvae, known as hornworms, immediately begin to feed on plant material, growing rapidly over two to three weeks. During this larval stage, they pass through five instars, or growth stages, shedding their skin to accommodate their increasing size. Once fully grown, the hornworm prepares for pupation by burrowing several inches into the soil.
The pupal stage is a period of significant reorganization, lasting from a few weeks to several months. The pupa is a hard, reddish-brown case with a distinctive loop-like structure at the anterior end, encasing the developing moth’s proboscis. The adult moth emerges from this pupal case during warm weather, unfolds its wings, and then seeks mates to begin the cycle anew.
Identifying the Hornworm
Hornworms are readily identifiable in their larval stage by several distinct features. They are large caterpillars, growing up to 3 to 4 inches (7 to 10 cm) in length, and are a vibrant green color. Their bodies are marked with white stripes along their sides, which vary between the two common species.
The Tobacco Hornworm (Manduca sexta) has seven diagonal white lines on each side of its body. Its most distinguishing feature is a prominent, curved horn at its rear end, which is red or orange-red. In contrast, the Tomato Hornworm (Manduca quinquemaculata) exhibits eight V-shaped white markings along its sides without black borders. Its horn, while also present at the posterior, is dark blue or black and is straighter. Both species primarily feed on plants in the Solanaceae family, including tomatoes, tobacco, potatoes, and peppers.