Bagworms and the Damage They Can Cause

In my area, one of the most serious bagworm moths is Thyridopteryx ephemeraeformis, the Evergreen Bagworm Moth. The moth thrives in the eastern United States, New England, and west as far as Nebraska. It is found south to the Gulf of Mexico and throughout Texas. With few predators in urban areas, the Evergreen Bagworm Moth often thrives in those habitats as well. In heavily forested areas, large populations are rare.

Arborvitae and red cedar are the favored host plants for the Evergreen Bagworm Moth. Cypress, spruce, juniper, pine, apple, birch, black locust, elm, maple, poplar, oak, sycamore, willow, and over 100 other species are also attacked. Both leaves and buds are subject to attack.

It is often easy to hand-pick bagworms when shrubs and trees are small. As the host plant grows larger, it frequently becomes impossible to hand-pick the worms and some type of insecticide is usually needed to stop infestations. When disturbed, a bagworm larva will retract into its case and hold the opening closed, thus making insecticidal sprays relatively ineffective. The best type of control for bagworms on trees and shrubs is a systemic insecticide. Systemics are applied to the ground around the plants and taken up by the roots. When the larvae then eat from the plant, they ingest the insecticide and die. Extension agents and other authorities frequently change the recommendations for the type of insecticide to be used against bagworms in order to help prevent the moths from developing immunity to a particular insecticide. Entomopathogenic bacteria, in particular Bacillus thuringiensis var. kurstaki, offer an effective natural control when applied to early instar bagworm larvae.

Bagworms are parasitized by ichneumonid parasitoid wasps, especially Itoplectis conquisitor. Predators include vespid wasps and hornets. Woodpeckers, sapsuckers, sparrows and mice will feed on the larva.

Bagworms on Arborvitae in my yard ...



It's easy to hand pick and destroy bagworms when the host plant is small.

The bagworm eventually produces a strong silk cord and attaches firmly to branches.

A mature larva may remain in the original host plant or drag its case to a nearby plant and attach for the pupa stage. Bagworms crawled to this small elm sapling and attached.


Bagworm on the move

Thyridopteryx ephemeraeformis, the Evergreen Bagworm Moth

Itoplectis conquisitor, a natural predator of the bagworm
(above photo courtesy Pennsylvania Department of Conservation and Natural Resources, License CC 3.0 US)