Native to the United States, the bagworm (Thyridopteryx ephemeraeformis) is a defoliating caterpillar in the order Lepidotera that commonly feeds on the foliage of many coniferous and deciduous trees east of the Rocky Mountains.

The bagworm’s self spun bag, which can be found hanging from the host plant by mid-summer is unsightly. Excessive feeding can strip away large quantities of leaves, causing branch dieback, and dead patches on the host plant.

Susceptible Species:

arborvitae (Thuja), fir (Abies), hemlock (Tsuga), juniper (Juniperus), pine (Pinus) and spruce (Picea), baldcypress, (Taxodium), black locust (Robinia pseudoacacia), honeylocust (Gleditsia triacanthos), sweetgum (Liquidambar styraciflua) and sycamore (Platanus occidentalis), boxelder (Acer negundo), cotoneaster (Cotoneaster), maple (Acer), elm (Ulmus), buckeye (Aesculus), willow (Salix), crabapple (Malus), linden (Tilia), poplar (Populus), and many more.

Pest

Thyridopteryx ephemeraeformis

Symptoms

• Stripping of the foliage, usually in the upper portions of the tree, in late summer

• Branch dieback, and dead, open patches are common on coniferous hosts.

Signs

• 1-1/2 inch to 2 ½ inch , cone shaped bags hanging from tree branches by late summer in which the larvae are enclosed.

• The larvae are mottled brown to black, but are seldom seen as they remain in the self spun bag.

• Adult males have clear wings and bodies covered in fur. Life Cycle • Eggs hatch in late spring. Young larvae emerge, construct a silk-like bag about 1/8 inch long around its body, and begin feeding on plant tissue.

• The larvae continue to feed into mid-summer until pupation begins. As the larvae feed and grow, the bag enlarges. Pupation lasts two to three weeks.

• By late summer the male adults emerge from the bag and mate.

• The females remain in the bag. After mating the female encases the egg mass, and remains in place until spring.

• One generation per year.

Distinguish from Look-alikes

• The bagworm’s self-spun bag hanging from tree branches can be a distinguishing sign.

• Eastern tent caterpillar form tent-like nests in the crotch of branches rather than cone-shaped bags that hang from the tree.

• Fall webworms form tent-like nests that enclose leaves at the branch terminals rather than cone-shaped bags that hang from the tree.

• Forest tent caterpillars form silken mats rather than cone-shaped bags that hang from the tree.

Bagworms are difficult to control because they often go undetected until it is too late in the season to treat effectively. It is important to treat the larvae before they mature because young larvae are more sensitive to chemical treatments. This means treatment in early spring to midsummer.

Picking bags off by hand can help to reduce populations, but is not always feasible. Look for bags during the winter to identify plants for treatment the following year.

Ohio State University

Penn State

Virginia Cooperative Extension

Johnson, W.T., Lyon, H.H. 1991. Insects That Feed On Trees and Shrubs.