Horned caterpillars are fascinating insects found in various environments, known for their distinctive horn-like projection at their rear. Their unique appearance often sparks curiosity about their ultimate transformation. This article explores the biological journey these larvae undertake and reveals the adult forms they eventually become.
The Process of Metamorphosis
Horned caterpillars, like many other insects, undergo a biological process known as complete metamorphosis, or holometabolism. This transformation involves four distinct stages: egg, larva, pupa, and adult. Each stage features a different appearance and set of behaviors.
Metamorphosis begins when an insect lays an egg, which hatches into a larva, the caterpillar stage. The larval stage focuses on eating and growing, with the caterpillar shedding its skin multiple times. After reaching its full size, the caterpillar transitions into the pupal stage. During this period, the caterpillar’s body transforms into its adult form. The characteristic “horn” present on the caterpillar is a feature of this larval stage and is shed when the insect pupates.
Common Horned Caterpillars and Their Adult Forms
Many common horned caterpillars transform into various species of moths, often large and visually striking.
The Tomato Hornworm (Manduca quinquemaculata) matures into the Five-spotted Hawk Moth. These caterpillars are large, pale green, up to four inches long, with white and black markings and a black horn. The adult Five-spotted Hawk Moth is a heavy-bodied moth with a four to five-inch wingspan, mottled gray-brown with yellow abdominal spots. These moths are often mistaken for hummingbirds due to their hovering flight.
The Tobacco Hornworm (Manduca sexta) develops into the Carolina Sphinx Moth. While resembling the tomato hornworm, it is distinguished by whitish diagonal lines and a reddish horn. The adult Carolina Sphinx Moth is also a large, heavy-bodied moth with hummingbird-like flight and six pairs of yellowish-orange abdominal spots.
The Hickory Horned Devil (Citheronia regalis) is the larval form of the Regal Moth. This caterpillar is one of the largest, growing up to six inches long, with a green body, black spines, and four stout, curved horns near its orange head. The adult Regal Moth is equally grand, with a wingspan up to six inches, displaying an orange-red body with yellow markings and gray wings adorned with red-orange veins and light yellow oval spots.
The Tersa Sphinx caterpillar (Xylophanes tersa) transforms into the Tersa Sphinx Moth. These caterpillars can be green or brown, with noticeable eyespots and a black horn. The adult Tersa Sphinx Moth has a wingspan of 2 3/8 to 3 1/8 inches, featuring grayish-brown forewings with a pale line and hind wings with contrasting black patches and pale spots.
The Purpose of the Horns
The “horn” or caudal horn is a distinctive projection on horned caterpillars’ rear. Despite their intimidating appearance, these horns are harmless and do not sting or contain venom. Their primary functions involve defense and deterrence against predators.
The horn may make the caterpillar appear more threatening, discouraging birds or other animals. Some theories suggest the horn aids in camouflage, allowing the caterpillar to resemble a broken twig, a thorn, or a small snake’s head, which helps it blend into its environment or startle threats. While less common, some researchers propose a minor sensory role or a function in stabilizing younger larvae as they move.