Bagworms

Table of Contents

• Injury
• Description
• Life History
• Management

Injury

Bagworms attack many deciduous and evergreen trees and shrubs. Young larvae feed first on the leaf surfaces and later they eat all but the larger veins. Trees may be almost completely defoliated due to the bagworms feeding. The preferred hosts include arborvitae, juniper, willow, maple, locust, sycamore and elm.

Description

The larvae or caterpillars construct a characteristic case or bag that they carry around with them, hence the name "bagworm". The size varies depending on the species. The larvae of the evergreen bagworm, Thyridopteryx ephemeraeformis, a common species, are 3/4 to 1 inch long when full-grown and vary in color from black to beige. The cases or bags are composed of silk, portions of leaves and twigs from the plant on which they feed. The adult males are small moths with well-developed wings; the females are wingless, legless and worm like.

Life History

Most bagworms overwinter in the egg stage in the bags of the female moth. In late May and June, the eggs hatch and the young larvae begin to construct their cases and carry them about as they feed. They feed through most of the summer and, in August when they are full-grown; they attach the case to a twig or side of a building or fence post, and pupate inside the case. In September and October the males emerge and fly about to locate a bag containing a female. Mating takes place without the female ever leaving the bag and she then lays the eggs, which will overwinter.

Management

Handpick bags from the trees and destroy them. If bagworms are found on the siding of the house or building, a stiff wire brush is helpful in dislodging them, but do not use on aluminum or vinyl siding as it will scratch and possibly ruin siding.

Insecticidal sprays can be used to control the young larvae and are most effective when applied in early June and July when the larvae are actively feeding. Either the insecticide Bacillus thuringiensis, spinosad, neem, acephate, carbaryl (Sevin), or malathion may be used. Be sure to follow manufacturer's directions carefully when using any pesticide.

This publication contains pesticide recommendations. Changes in pesticide regulations occur constantly and human errors are still possible. Some materials mentioned may no longer be available and some uses may no longer be legal. All pesticides distributed, sold or applied in New York State must be registered with the New York State Department of Environmental Conservation (DEC). Questions concerning the legality and/or registration status for pesticide use in New York State should be directed to the appropriate Cornell Cooperative Extension Specialist or your regional DEC office. READ THE LABEL BEFORE APPLYING ANY PESTICIDE.