Spongy Moth

What it does

The damaging stage is the caterpillar, which feeds heavily on tree leaves in late spring and early summer. During outbreaks, huge numbers can defoliate whole stands of oaks and other hardwoods, stressing and sometimes killing trees. Young caterpillars can balloon on silk threads in the wind, spreading to new trees over short distances.

Where it lives

It is established in the northeastern US and parts of the Midwest and Southeast, in forests, woodlots, parks, and yards with oaks and other hardwoods. Egg masses are laid on tree bark and any sheltered outdoor surface, including firewood, vehicles, and outdoor gear, which is how the pest spreads to new areas.

How it breeds

There is one generation a year. Fuzzy tan egg masses laid in summer overwinter and hatch the next spring into caterpillars that feed and grow, then pupate. Adults emerge in mid to late summer to mate and lay eggs; in the established European lineage the females do not fly, so egg masses on moved items drive spread.

What it eats

Caterpillars feed on the leaves of many trees, strongly preferring oaks but also eating aspen, birch, willow, apple, and hundreds of other hardwoods and some conifers. This broad appetite is what makes outbreaks so destructive to forests and landscape trees.

Identification

Mature caterpillars are dark and hairy, up to about 2.5 inches, with a distinctive row of five pairs of blue spots followed by six pairs of red spots along the back. Adult females are near-white and heavy-bodied; males are brown and fly. Egg masses are buff, felt-like, and spongy, the source of the current name.

Signs of an infestation

• Trees stripped of leaves in late spring or early summer
• Large hairy caterpillars with blue and red spots
• Fuzzy tan, spongy egg masses on bark and surfaces
• Frass (droppings) raining down beneath infested trees
• Clusters of caterpillars on trunks and outdoor structures

Prevention tips

• Inspect and scrape egg masses from bark and surfaces in winter
• Check vehicles, firewood, and outdoor gear before moving them
• Do not transport firewood long distances
• Follow local quarantine rules for moving outdoor items
• Report suspected new infestations to state agriculture officials

Professional solutions

Managing spongy moth on landscape trees, or during regional outbreaks, often involves professionals and government programs using pheromone monitoring, targeted biological or growth-regulator treatments, and area-wide suppression. Arborists can help protect high-value yard trees, and state agencies coordinate broader control and quarantine efforts.