White eggs are laid in masses on the undersides of leaves. As soon as they hatch, larvae begin to spin webs over the foliage and feed on the enclosed leaves. The web grows as larvae grow and eat foliage. Larvae remain clustered, usually not crawling away from the web until ready to pupate. Although the webs are unsightly, they usually do little serious damage to plants because defoliation occurs in late summer when deciduous trees and shrubs are going dormant.
Fall webworms have many natural enemies that ordinarily keep the numbers down.
But every few years the numbers increase and trees become heavily infested. For small trees, webworm nests can be cut out and destroyed. Several serious fires have been started by people doing this. Spot treatment with chemical pesticides is effective when applied in June as larvae start to make webs. Where infestations are severe, spray the entire tree to avoid having to repeat the treatments.