Bagworm: what the agencies record

This page describes what the named sources say. It is not a diagnosis of any tree and does not say what should be done with one. The bagworm (Thyridopteryx ephemeraeformis) is a native North American caterpillar, and none of the four pages read lists it as regulated or notifiable. Each section names its source, all read on October 8, 2026. The parent page, insect pests of trees, compares it with the other pests on the list.

Names

All four sources use the common name bagworm and the scientific name Thyridopteryx ephemeraeformis. The Missouri Botanical Garden places it among the Lepidoptera, the moths and butterflies.

What the sources say to look for

The Missouri Botanical Garden says the most notable sign is the protective bag attached to a branch. It describes bags built from bits of twigs and leaves of the host plant, 1 to 2 inches long, that resemble Christmas tree ornaments. NC State Extension describes a cone-shaped bag of silk with bits of host plant and other debris, from 1/4 inch to over 2 inches as the caterpillar grows, and says larger bags hang down from branches. Purdue Extension says the bags blend in so well with the tree that they can be missed until a lot of damage has been done.

The caterpillars are rarely seen outside the bag, NC State says. Purdue says they crawl part way out to feed and retreat inside when disturbed. The Morton Arboretum says young caterpillars feed on the upper leaf surface and may make small holes, while older caterpillars can consume entire needles or leaves.

Hosts

NC State says bagworms are most common on conifers such as leyland cypress, arborvitae, cedar, juniper and pine, and have a wide host range that includes many deciduous trees and shrubs. The Morton Arboretum names arborvitae and junipers as the most frequent hosts and says both evergreen and deciduous trees can be fed on. The Missouri Botanical Garden says the insect feeds on over 128 plant species, most commonly arborvitae, red cedar and other junipers, and also lists fir, maple, juneberry, buckeye, persimmon, ginkgo, honeylocust, larch, sweet gum, spruce, pine, sycamore, poplar, oak, locust, willow and hemlock. Purdue names arborvitae and junipers.

On damage, the Morton Arboretum says a severe infestation may defoliate plants, which can kill branches or entire plants, and says a defoliated evergreen cannot push out another set of leaves, while a healthy defoliated deciduous tree may produce a new flush. NC State says defoliation over multiple years can reduce growth or cause sparse foliage, and that large sections of evergreens may be killed outright.

Life cycle as the sources state it

All four sources give one generation a year. Eggs overwinter inside the female's bag and hatch in spring. NC State gives hatching in May and June, the Missouri Botanical Garden late May to mid-June, the Morton Arboretum early June in northern Illinois, and Purdue early June in Indiana. NC State describes newly hatched larvae spinning down on silk threads blown by wind, which it calls ballooning, and the Morton Arboretum also says silk threads let wind carry them to other plants.

Caterpillars build a bag at once and enlarge it as they grow. The Missouri Botanical Garden says the full-grown larva is about one inch long and that in mid-August mature larvae attach the bag to a twig, close it and pupate, with adult males emerging by mid-September. NC State says August and September for the adult stage and describes a silk band wrapped around a twig. The adult female has no wings, is maggot-like or grub-like in the descriptions, and never leaves the bag. The male is a small black or brown furry moth with clear wings that flies to a female's bag. The Missouri Botanical Garden and NC State give 500 to 1,000 eggs per female, the Morton Arboretum up to one thousand, and Purdue over 1,000 bagworms from each female bag.

Purdue adds a note on winter: it says eggs in bags south of Monticello, Peru and Bluffton, or near Lake Michigan, usually survive the winter in Indiana, and that in other parts of the state eggs can be killed during cold winters. Because females do not fly, NC State says infestations can be concentrated and localized, for example four or five trees in a hedge row of 50.

Where it is reported

NC State says bagworms occur throughout North Carolina and the eastern United States. The Morton Arboretum puts the bagworm across a large part of the eastern half of the United States, and the Missouri Botanical Garden says its bags are on trees and shrubs throughout the United States. Purdue says bagworms are common throughout Indiana. No national count of locations is given by the pages read, so none is given here.

Regulated status and reporting

None of the four pages names a regulation, quarantine order or report line for the bagworm, and each describes it as a landscape pest handled through extension advice. For the agencies that do take reports of regulated pests, see the guide on reporting a pest in the United States.

Management as the sources list it

The Missouri Botanical Garden calls hand-picking the bags the most economical method and says birds and insect predators feed on larvae. NC State lists planting less susceptible species where bagworms are common, removing bags by pruning infested branches or hand-picking, and notes parasitic wasps. It says bags removed in fall and winter hold eggs, so removal then makes a difference in spring. The Morton Arboretum says hand-picking is feasible on smaller trees and shrubs, that bags should be destroyed, and that natural enemies do not provide effective management when populations are high. Purdue describes picking bags off before the eggs hatch.

All four sources also describe insecticide use against young caterpillars, with the Morton Arboretum and Purdue saying that once the bag is closed and tied to a stem or the larvae are mature, sprays no longer work. NC State says contact insecticides may fail because the bag is waterproof. This page gives no product names, rates or timings. For who may apply pesticides, see pesticide licences.