bagworms

Bagworms are the larval stage of moths in the family Psychidae. They are known for constructing protective cases or bags from silk and pieces of plant material, which they carry as they move. These cases can be attached to branches and often resemble small, conical seed pods. The evergreen bagworm, Thyridopteryx ephemeraeformis, is a common pest in North America.

Most bagworms overwinter as eggs inside hollow bags. In spring, eggs hatch and larvae emerge, feeding and enlarging their bags as they grow through several molts. They eventually pupate inside the bag. In many regions, one generation occurs per year, though warmer climates may support two or more. Adults are short-lived; females are typically wingless and remain in or near their bags, while males are winged and mate with wandering males.

Bagworms feed on a wide range of trees and shrubs, with favorites including juniper, arborvitae, pines, and other ornamentals. Heavy feeding can defoliate branches and cause dieback or tree decline, especially with repeated outbreaks. Signs of infestation include rows of hanging bags (about 1–2 inches long, up to several centimeters) on branches and a general thinning of foliage.

Management and control options include mechanical and cultural methods, biological controls, and, when necessary, chemical treatments. Manual removal of bags in late fall or winter and pruning and destroying infested branches can reduce populations. Bacillus thuringiensis kurstaki (Bt) is effective against young larvae; spinosad can also be used. Pheromone traps may help monitor male moth activity. Maintaining plant vigor and removing alternate hosts can reduce susceptibility. For severe or widespread outbreaks, professional arborist consultation may be advised.