Polyphemus Moth Caterpillar

The Polyphemus moth caterpillar is the larval stage of one of North America's largest and most recognizable silk moths, named for the mythological one-eyed giant because of the huge eyespots on the adult's hindwings. The caterpillar itself is a heavyset, cylindrical eating machine that spends its entire larval life devouring leaves before transforming into a moth with a wingspan that can exceed five inches.

These caterpillars are generalist feeders on a wide variety of deciduous trees, which allows them to turn up in backyards, parks, and forest edges across much of the continent. Despite their large size, they are docile and slow-moving, relying on camouflage rather than aggression to avoid predators.

• Thick, cylindrical body that is bright to lime green, growing to roughly 3.5-4 inches long
• Each body segment bears small silvery or yellow, oval-shaped tubercles arranged in rows
• A faint yellow or reddish diagonal line often runs along the sides
• Sparse, short setae (bristles) project from the tubercles but are not conspicuous
• Head is small and rounded, colored pale green to tan
• Lookalikes include other giant silk moth larvae such as the Luna and Cecropia caterpillars, which share the plump green body but differ in tubercle color and arrangement

Polyphemus caterpillars are found across most of the United States and southern Canada wherever suitable deciduous host trees grow, from oak-hickory forests to maple-lined suburban streets. They feed high in tree canopies as well as on low shrubs and are active from late spring through summer, depending on the number of generations in a given region.

The caterpillar is a solitary leaf-feeder with an enormous appetite, capable of consuming many times its body weight in foliage as it grows through five instars. It relies on cryptic green coloration to blend with leaves and will thrash its body or emit a clicking sound with its mandibles if disturbed. In the broader ecosystem it serves as an important food source for birds, and its cocoon can be parasitized by tachinid flies and parasitic wasps.

Females lay flat, disc-shaped eggs singly or in small groups on host leaves. After hatching, the caterpillar passes through five instars over several weeks, growing from a tiny black-headed larva into the large green form. When mature, it spins a tough, papery oval cocoon wrapped in a leaf, often dropping to the leaf litter, and pupates inside. Depending on climate, the species overwinters as a pupa and produces one generation per year in the north or two in warmer southern regions before emerging as an adult moth that does not feed.