Return to main page

BAGWORMS

These small brown caterpillars surround themselves with tapered bags made from
foliage and silk. Each bagworm drags its bag around while feeding, eventually
attaching the bag to a branch with silk to pupate within. As adults emerge, males fly,
but females stay within the bag waiting for a mate. Larvae hatch and depart the bag to
feed, each building its own bag.

SIGNS Brown pouches, about 1 to 3 inches long, hang from stems in many species
of evergreen or deciduous trees and shrubs. Chewed leaves appear in spring, starting
at the top of plants; branches or whole plants may be defoliated. Serious infestations
can kill evergreens, but deciduous trees leaf out again.

PREDATORS Parasitic wasps and flies.

CONTROL Handpick bags and destroy them before the larvae hatch in spring. Spray
plants with Bt in spring and early summer before the worms are well established in
their bags.

The bagworm, Thyridopteryx ephemeraeformis (Haworth) is the larval stage of a moth that is reported to feed on over 100 different plants. It is most common in the climates, where populations can build up rapidly and become serious pests. On pine trees, its cone-shaped bags are often mistaken for cones, which go unnoticed until the infestation is severe. Bagworms spread slow because the female is unable to fly, however, bagworms can be windblown or crawl to other host plants and can also spread through infested nursery stock.

Plants Attacked

Bagworms attack both deciduous and evergreen trees. Some of the more common evergreen host plants include arborvitae (Thuja), fir (Abies), hemlock (Tsuga), juniper (Juniperus), pine (Pinus) and spruce (Picea). Deciduous host plants include black locust (Robinia pseudoacacia), honeylocust (Gleditsia triacanthos), sweetgum (Liquidambar styraciflua) and sycamore (Platanus occidentalis).

Insect Identification

The cone-shaped bags, which they form, easily identify bagworms. These are carefully interwoven using silk and bits of leaves and twigs from the host plant resulting in a well-disguised covering. The tops of the young larvae are shiny black and their body undersides are dull amber. When fully grown, the bagworms are a dull, dirty, gray with darker markings toward the head. The adult male develops into a moth that can fly, but the female remains grub-like and stays inside the bag.

Life History

Winter	The eggs over-winter inside the bag made by the previous year's female.
Spring	Egg hatch occurs from late May to early June, at which time the larvae crawl out in search of food. Each constructs a small bag around its hind parts with silk and plant material.
Summer	Feeding, growth and molting continue until August, at which time the mature larvae attach themselves to twigs. They close the bag and reverse themselves so that they are head down in the bag. They remain there for about 4 weeks as pupae.
Fall	During September and early October, the female releases a sex attractant pheromone and the males leave their cases and fly to the female bags to mate. Females lay 500-1000 eggs in each bag. There is one generation per year in Pennsylvania.

Damage Symptoms

The young larvae feed on the upper epidermis leaving small brown spots on the leaves. Older larvae strip evergreens of their needles and consume whole leaves of susceptible deciduous species, leaving only the larger veins. Unfortunately, the presence of bagworms often goes unnoticed until they are mature and the damage is extensive.

Bagworm insecticides:
Formulations of acephate, azadirachtin, Bacillus thuringiensis, bifenthrin (Bifenthrin Pro Multi-Insecticide, Onyx Insecticide, Talstar F, Talstar Lawn & Tree Flowable, Talstar GC Flowable, Talstar Nursery Flowable, and TalstarOne Multi-Insecticide only), carbaryl, chlorpyrifos (Dursban 50W only), cryolite, cyfluthrin, cyfluthrin and imidacloprid, deltamethrin, diflubenzuron, dimethoate, lambda-cyhalothrin, malathion, permethrin, pyrethrins and piperonyl butoxide, spinosad, tau-fluvalinate, tebufenozide, and trichlorfon are labeled for bagworm management.

Management Hints:
Bagworm cases (containing overwintering eggs) can be handpicked from infested host plants during winter and early spring. Otherwise, management measures can be applied after eggs hatch and caterpillars are small during early to mid-June.

Biological	The bagworm has some natural enemies, such as certain species of birds that are able to tear open the bags and feed on the larvae, in addition to insect predators and parasitoids. Unfortunately, this will not usually control the bagworm population.
Mechanical	In the fall, winter and early spring, before the eggs have hatched, the bags can be picked off the plant and destroyed.
Chemical	Insecticides are more effective when the larvae are small and just emerging from the over-wintering bag. Larger larvae and molting larvae are not easily killed.