A hornworm is a type of caterpillar. Hornworms are the larval stage of moths belonging to the family Sphingidae, commonly known as hawk moths or sphinx moths. These creatures are often encountered as garden pests due to their voracious feeding habits during their caterpillar phase.
Understanding the Hornworm as a Caterpillar
Hornworms are large, cylindrical caterpillars, typically green in color, which provides effective camouflage among plant foliage. They are notable for a distinct, horn-like projection found on their posterior end, which gives them their common name. This horn is not a sting and is harmless. Two of the most common species are the tomato hornworm (Manduca quinquemaculata) and the tobacco hornworm (Manduca sexta).
These two hornworm species, while similar in appearance and habits, have distinguishing features. The tomato hornworm has eight V-shaped white markings along its sides and a black horn, while the tobacco hornworm displays seven diagonal white stripes with black borders and a red horn. Both species reach a size of 3 to 4 inches in length by maturity. Hornworms are primarily herbivores and feed on plants in the Solanaceae family, which includes common garden vegetables such as tomatoes, tobacco, potatoes, peppers, and eggplants.
The Hornworm’s Journey: From Larva to Moth
The hornworm’s existence as a caterpillar is just one phase in its complete metamorphosis, a four-stage life cycle that includes egg, larva, pupa, and adult. The life cycle begins when the female hawk moth lays tiny, spherical, greenish-white eggs, usually singly on the underside of host plant leaves. After 3 to 5 days, the eggs hatch into the larval stage, which is the hornworm caterpillar.
During the larval stage, the hornworm feeds and grows rapidly, shedding its skin multiple times through a process called molting, typically going through five to six instars over a period of two to four weeks. Once fully grown, the mature caterpillar burrows into the soil, usually 4 to 6 inches deep, to enter the pupal stage. The pupa is a hard, reddish-brown case, about 2 inches long, and has a distinctive loop. Hornworms typically overwinter as pupae in the soil, with adults emerging the following summer.
The final transformation results in a large adult moth, commonly known as a hawk moth or sphinx moth. These moths are typically gray-brown with a wingspan ranging from 4 to 5 inches, and they have distinctive yellow or orange spots on their abdomens. Unlike their destructive larval stage, adult hawk moths are nectar feeders and are known for their agile, hovering flight, often resembling hummingbirds.