Bag Worm Control

This pest overwinters as eggs inside the female’s abdomen inside the bag she constructed. Females lay 500-1000 eggs in each bag during the previous fall. Eggs start hatching from late May through early June. Upon hatching, young larvae crawl out of the bag and start to feed and construct silken shelters over their bodies. As the larvae (Image 1) grow over the eight to ten week feeding period, they continue to enlarge the exterior of their bags with pieces of foliage, bits of bark, or other plant parts. Feeding and development usually continue until August. Mature larvae loop strands of silk around a twig and become firmly attached. After the top of the bag is closed, larvae reverse their position in the bags so that their heads face downward. They then change into the pupal (resting) stage and remain in this life stage for about 4 weeks. During September and early October the males (Image 2) leave their cases and fly to bags containing females where mating takes place. Each mated female deposits a mass of eggs inside her bag. She crawls out of the bag after laying eggs, drops to the ground and dies. This pest species spends the winter inside the bag until the following spring. There is only one generation a year in Pennsylvania.