Plaster Bagworm, Vol. 9, No. 30
Phereoeca uterella
Order: Lepidoptera
Family: Tineidae
“We have things that look like seed crawling up the wall in the garage. What are they?”
Plaster bagworms, a.k.a. household casebearers, belong to the same family as clothes moths. The caterpillars live inside flattened, oval-shaped, brown to gray bags that are around ½ inch long when the caterpillars are fully mature. These bags superficially resemble seed of squash or some other plant. The caterpillars move by extending their bodies forward, grasping the surface with their legs and mandibles and drawing the bag forward. There is an opening at each end, allowing the caterpillars to switch ends when they need to change directions. Household casebearers are usually associated with spider webs, feeding on the web as well as the dried dead insect parts located there.
Spider webs are one of their favorite foods, but they can also feed on wool and other animal-based fibers, including silk, feathers and accumulations of human hair and dandruff. On rare occasions they damage clothing and other fabrics. Infestations often originate under furniture, light fixtures, closets or other out of the way places where spider webs and dead insects accumulate. Plaster bagworms are more common in the southern portion of the state, presumably because of their preference for high humidity. Heaviest infestations are often seen in garages, carports, storage rooms and similar non-air-conditioned sites with lots of spider webs.
Larvae wander about just before pupating, and this is when most infestations are noticed. Heavy infestations most commonly occur in situations with high humidity. The adults are small, inconspicuous moths that are rarely noticed. When resting with wings folded, the tan to brown moths are about ¼ inch long with a fringe of long hairs at the tips of the wings. Like most clothes moths, they have fuzzy heads covered with short hairs.
Control: For general infestations in rooms and storage areas, vacuuming and cleaning the infested area is usually all that is required. The caterpillars can be killed by spraying with products that contain pyrethroid insecticides such as cyfluthrin, deltamethrin, bifenthrin, cyhalothrin, or permethrin and are labeled for use in the sites being treated, but the bags, and the spider webs, must still be removed by vacuuming or sweeping. Infestations in clothing and other fabrics should be treated as for clothes moths. See pages 16-19 of Extension Publication 2443, Control Household Insect Pests.
For information on insects that most commonly damage clothing and other fabrics see these short articles on: varied carpet beetles, case-bearing clothes moths, and webbing clothes moths.
Blake Layton, Extension Entomology Specialist, Mississippi State University Extension Service.
The information given here is for educational purposes only. Always read and follow current label directions. Specific commercial products are mentioned as examples only and reference to specific products or trade names is made with the understanding that no discrimination is intended to other products that may also be suitable and appropriately labeled.
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