Spring Cankerworm Invasion: Managing the "Raining Caterpillars"

Thousands of green caterpillars descending on silk threads from oak trees? That's spring cankerworm (Paleacrita vernata). Here's what's happening and what you can (and can't) do.

Understanding the Cycle

Cankerworm caterpillars feed in tree canopies for 4-6 weeks in spring. When mature, they drop on silk threads to pupate in soil. The "black pellets" are frass (insect droppings). Adult moths emerge in late fall/winter—females are wingless and climb trees to lay eggs.

Management Options

• B.t. (Bacillus thuringiensis): Effective on young caterpillars but difficult to apply high in trees.
• Tree bands: Sticky bands on trunks in fall trap wingless females before egg-laying.
• Soil cultivation: Light tilling around trees in fall exposes pupae to predators/weather.
• Patience: Most trees tolerate defoliation and releaf. Outbreaks are cyclical.

What NOT to Do

Don't spray broad-spectrum insecticides—they kill beneficial insects that naturally control cankerworms. The "cankerworm sorbet" recipe at the link is a humor piece, not a control method!