Evergreen Bagworms
About Bagworms
Those little brown brown sacks hanging off your evergreen plants aren’t pine cones or parts of the plant. They are cocoons with moth larva inside! These moths begin their life in the spring time, build their cocoon throughout the summer, hatch into adults, and mate at the end of the summer.
They hatch from eggs within the carcass of their mother, inside her cocoon. The larva then crawl to a nearby plant and begin creating a case from silk, fecal material, and leaves from its host. Bag worms don’t exclusively feed on evergreen plants, but they do prefer them. As the larvae grow, they add on parts of the plant to create their cocoon. This adds camouflage as well as rigid structure to their cocoon. Once their cocoon is complete, they find a spot to hang on the plant, then spend 4 weeks transforming into adults. Males turn into flying adults while females remain in the cocoon waiting for the male to find her to mate.
Why they are harmful
As with all animals, bagworms play an important role in the environment. However, they can kill plants and are quite the pest. Bagworms put stress on a plant in two ways. They cut away leaves and pine needles to eat and to create their cocoon. They also create a loop of silk that goes around a branch of the plant to hang their cocoon from. This silk is so strong it acts like a noose, chocking out nutrients for the end of the branch. The combination of these habits over a couple years of activity, will prove fatal for a plant.
Treatment Options
Treating host plants with a residual insecticide will prove the most effective way to remove the species. In the spring time when the eggs have just hatched, in the summer when they are foraging, and in the late summer when they are mating, are all good times to act.
