These invasive insects look like cone-shaped sacs that can sometimes be mistaken for pine cones. The sacs look like cocoons that hang from the tree branches. These cocoons or sacs contain bagworm eggs and once they hatch, they will begin to dine on the leaves and needles of your trees and shrubs. A heavy infestation on evergreens can cause extensive die-back and even death to the plant. Bagworms are fond of a variety of trees such as blue spruce, cedars, white pines and junipers. On deciduous trees, bagworms will strip the leaves, leaving only bare branches.
Left untreated, bagworms can defoliate branches, causing branch die-back and eventually kill the shrub or tree. The best defense against bagworms is an insecticide spray application. If the outbreak is severe, a second application may be required.