Spiny Oakworm

Systematic position. The Spiny Oakworm (Anisota stigma) belongs to the order Lepidoptera and the family Saturniidae (giant silkworm moths). It is a well-known forest insect species native to North America, recognized for its specialized feeding habits on deciduous trees.

Host plants. The primary hosts for Anisota stigma are various species of oak (Quercus). While they show a strong preference for oak trees, they can occasionally be found on other hardwood species if host populations are dense and food competition is high within a specific area.

Biology and life cycle. This species typically produces one generation per year. The moths emerge in the summer, and females lay large clusters of eggs on the underside of host leaves. Larvae emerge and exhibit gregarious behavior in their early instars. The life cycle concludes with the larvae burrowing into the soil to pupate and overwinter as pupae.

Damage and severity. Young larvae skeletonize leaves, while older instars consume entire leaf blades, leaving only the main veins. High populations of Spiny Oakworms can cause significant defoliation, stressing the host trees and reducing their annual growth rate, which can lead to long-term decline if infestations persist over multiple years.

Protection measures. Management strategies include:

• Monitoring egg clusters during early summer.
• Manual removal of larval colonies in small or residential trees.
• Application of Bacillus thuringiensis (Bt) sprays targeting early-instar larvae.
• Using systemic or contact insecticides only in severe cases where tree health is at immediate risk.