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Bagworm
David Keith, Extension Entomology Specialist
May 23, 2001
PEST IDENTIFICATION & DAMAGE
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Bagworm |
Common Name:
BagwormScientific Name:
Thyridopteryx ephemeraeformis (Haworth), Lepidoptera: Family Psychidae.Identifying Characteristics for Damaging Stage(s):
Look for tapered "sacks", varying in size from 1/4 to 1 ½ inches long on infested host trees and shrubs. Bagworms are caterpillars that live inside a tough, protective sack made of silk and plant material that is attached to the host plant. When feeding, the insects move along the stem and enlarge the bag at each molt, incorporating pieces of leaves or stems into the bag. While the worms are difficult to remove from their individual sacks, this can usually be accomplished with a slow, steady pull of the fingers. The bodies of the worms are generally tapered, grayish green to black, and from 1/4 to 1/1/4 inch long. There are light, mottled patterns on the head "capsule" of the larvae. Adult male moths are 1 inch long, and black with clear wings and are strong fliers. Female moths are wingless, legless and largely shapeless and remain inside the bags, falling to the ground when egg-laying is complete.Damage/Nature and Symptoms:
This insect has chewing mouthparts in the caterpillar (larva) stage and feeds on tree foliage. Heavily infested trees and shrubs lose foliage to feeding worms, eventually turning brown as they die. These will be covered with the tapered sacks, each with a caterpillar inside. Damage will be at its greatest during late July, August and September. Since evergreens do not recover well from feeding, many shrubs are killed in the third or fourth year of infestation. |
Bagworm Damage |
DISTRIBUTION AND LIFE CYCLE
Distribution:
Generally distributed throughout the eastern U.S. to Nebraska. These insects usually attack evergreens and conifers, including pines, spruce, junipers, arborvitae and red cedar, although they feed on various deciduous trees such as maple, oak, sycamore, apple and hawthorn as well. Fitzer junipers in particular are often heavily attacked.Summary of Life Cycle:
Bagworms winter as eggs inside the pupa case of the females. Several hundred eggs may be contained in a single bag from the previous season. Eggs hatch in Nebraska in mid-June and young caterpillars disperse over the foliage of juniper shrubs, each making a tiny initial "bag." Each insect hangs by its legs, moving along the branches as it feeds, incorporating leaf material into the silk as it enlarges its protective and portable "home." Most of the damage occurs in July and August as the worms are approaching full size, therefore controls should be applied in late June or early July to prevent damage. In late August and September, the worms transform to the pupa stage and male moths, which have clear wings, begin to emerge. Females remain inside their sacks and males accomplish mating by pairing with each female by inserting their own abdomens into each bag. Once mated, the female deposits eggs into its old pupa case, in a matrix of frothy material produced by special glands in her abdomen. When finished, she exits the bag and drops to the ground, leaving behind the egg mass. There is only one generation per year.MANAGEMENT METHODS:
Inspection/Survey Methods:
In June, examine junipers, pines and other evergreens for evidence of bags and feeding. Keep a close watch on species such as oak, hawthorn, apple or other trees placed in close proximity to infested evergreens in landscape plantings.Non-Chemical Management Strategies:
: Search for and carefully remove all bags to avoid reinfestation in the spring. This may be done in late fall, winter or early spring, prior to the June hatch. All removed bags should be burned, buried or composted deeply so that hatching worms do cannot easily move to nearby plantings. One of the easiest and most efficient control measures is to apply a safe, natural caterpillar disease-causing agent, Bacillus thuringiensis, available as Dipel, Javelin, Biotrol or Bactur each spring after young worms have hatched out and begun to feed. While the disease will kill larger caterpillars as well, it is important to prevent the greatest amount of leaf feeding, so it should be applied early when worms are small.Chemical Management Strategies:
Chemical management with insecticides is also effective if done before much feeding is accomplished.For the latest information on available chemical controls, consult the Pesticide Selection Guide.