Tent Caterpillars and Webworms

- More unsightly than damaging -

Summary: Certain caterpillars (moth larvae) cover their host plants with silken tents that can look like massive spider webs. Larvae feed inside these protective tents. Generally, damage from "tent caterpillars" is fairly limited and control is only rarely needed.

Jack DeAngelis, PhD
OSU Ext. Entomologist (ret.)

A number of different moth larvae construct silken tents as they feed on the leaves of their host plants. The tents are often large, distinctive and attract attention because they can resemble huge spider webs (see photo right). Larvae may be found crawling on the outside or inside of tents depending on species and stage of development. Tents are frequently covered with frass (caterpillar feces) and plant debris. Adult moths are fairly large with greater than 1" wingspan but otherwise usually drab.

While occasional outbreaks of these insects cause serious damage to forest trees, for ornamental trees and shrubs the damage is usually more unsightly than damaging. It has been shown experimentally that healthy trees and shrubs can sustain considerable foliage loss without permanent injury.

common names: forest tent caterpillar, western tent caterpillar, eastern tent caterpillar, fall webworm

western tent caterpillar on wild rose

A western tent caterpillar "tent" and larvae on wild rose (photo by JD DeAngelis, copyright 2006). Note large larvae on surface of tent (left center).

Control of tent caterpillars

Landscapers and gardeners can simply clip and destroy the tents to control these defoliators. There are many natural enemies that target this group of insects as well which probably accounts for their spotty occurrence and limited damage. If chemical treatment is necessary there are low toxicity microbial insecticides available. The bacterium Bacillus thuringiensis (Bt) specifically targets insects and is harmless to other organisms, including us. Different strains of Bt target different insects so be sure to read the label carefully. B.t. kurstaki is the strain for use against caterpillars. Current brands of B.t. kurstaki for caterpillars are: DiPel, Biobit, Thuricide, and others.

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