How to identify a spongy moth
The spongy moth shows strong differences between the sexes. Males have a roughly 1.5-inch wingspan, are gray-brown, and have feathery antennae and dark wavy bands across the forewings; they are restless fliers seen by day as well as at night. Females are larger, creamy white with thin dark zigzag lines, and have heavy bodies; they are essentially flightless and tend to sit on trunks and walls. Both are best confirmed by their tan, fuzzy-looking egg masses plastered on bark, firewood, outdoor furniture, and vehicles.
Where it lives
This is an introduced species, not a native one, and its established range covers the Northeast and upper Midwest with ongoing spread. Open occurrence records concentrate in New York, Massachusetts, Michigan, Pennsylvania, and Vermont, which are squarely within its core infested zone. It thrives in oak-rich forests, suburbs, and woodlots, and outbreaks can defoliate large blocks of trees in a single season.
When it flies
Adults emerge and fly mainly in June and July, the short window when males search out the stationary females to mate. The damaging life stage, the caterpillar, is active earlier in spring and into early summer before the adults appear.
Caterpillar, host plants, and life cycle
The caterpillar is the destructive stage: a dark, hairy larva with five pairs of blue spots followed by six pairs of red spots down its back. It feeds on oak above all but will eat hundreds of species of trees and shrubs, and heavy infestations can strip whole canopies. After feeding, larvae pupate, and the short-lived adults emerge only to reproduce. Females lay buff egg masses that overwinter, which is the main way the species hitchhikes to new areas on moved firewood and outdoor gear.
How to see one (and why to report it)
Because it is an invasive pest, the spongy moth is one moth worth watching for and reporting to local agriculture or forestry authorities, especially the egg masses. Males come to UV and mercury-vapor lights more readily than to white LEDs, so a light and sheet on a June or July night will often turn them up. Keep in mind that artificial light works by disrupting moth flight orientation rather than truly attracting them, so a still, warm night gives the best showing. Not sure what you are looking at? Try our what moth is this guide, compare it with the native forest tent caterpillar moth, or check tonight's likely moths for your area.