Anisota finlaysoni

Description

Finlayson's Oakworm Moth (Anisota finlaysoni) is a medium-sized moth in the giant silkworm moth family (Saturniidae). Described by Riotte in 1969, it is one of several North American Anisota species whose larvae are specialized oak feeders. The common name "hornless" refers to the smooth appearance of the caterpillar, which lacks the prominent thoracic horns found in some related silkworm larvae.

This species is listed as Threatened under Ontario's Endangered Species Act, 2007, and is on the Protected Species in Ontario List. Its provincial range is tightly linked to the distribution of oak-dominated woodlands in the Carolinian zone.

Lifecycle

Anisota finlaysoni produces one generation per year. Adult moths emerge in mid to late summer (July through August) and mate shortly thereafter. Females deposit eggs in clusters on the leaves of oak host trees.

Larvae feed gregariously on oak foliage through late summer and early fall, passing through several larval instars as they grow. When fully grown, caterpillars descend from the host tree to pupate in the soil, where they overwinter as pupae. The following summer, adult moths emerge to repeat the cycle. Adults are short-lived and, as is typical of many Saturniidae, have reduced or non-functional mouthparts and do not feed.

Ecology

Larvae are obligate oak feeders, consuming the foliage of various Quercus species. Like many oak-specialist Lepidoptera, they are part of the rich insect community supported by oaks, which are keystone plants hosting over 500 Lepidoptera species in eastern North America. Larval feeding can occasionally cause noticeable defoliation, though populations are naturally controlled by parasitoids, predators, and disease.

Adult moths serve as prey for bats, birds, and other insectivores during their brief flight period. The species' reliance on oak woodlands makes it vulnerable to habitat loss, forest fragmentation, and pesticide applications targeting other Lepidoptera (such as Spongy Moth control programs).

Host Plants

Larvae feed exclusively on oak species (Quercus). Documented and likely hosts in Ontario include:

• Quercus prinoides
• White Oak (Quercus alba)
• Black Oak (Quercus velutina)
• Other oak species within the Carolinian zone

Habitat

In Ontario, Finlayson's Oakworm Moth is restricted to oak-dominated woodlands and savannas in the Carolinian forest region. Its reliance on oak hosts limits it to the southernmost parts of the province where oak communities persist — a zone that has experienced extensive habitat loss to agriculture and urban development.

The broader North American range includes oak forests of the eastern United States. In Canada, it is native and documented from southern Ontario, where remaining populations depend on the conservation of mature oak stands and savanna remnants.