Types

• Bagworms are common pests of many narrow-leafed evergreens, including juniper, arborvitae, cedar and cypress. This caterpillar is the larval form of an adult moth, with male moths having a one-inch wing span and female moths having no wings. Bagworms are known for the brown bags they place on host evergreens. These bags resemble pine cones, and are constructed from bits of plant debris and silk.
  
  Another caterpillar that feeds on the foliage of evergreens is the larvae of the gypsy moth. Gypsy moth larvae are hairy caterpillars that hang from silken threads suspended from evergreen leaves. Arborvitae and junipers are often infested with gypsy moth larvae, but are not favored hosts of this caterpillar. Gypsy moth larvae typically feed on these evergreens after all other plants in close proximity have been heavily infested with larvae. The adult form of the male gypsy moth is a brown flying moth and female moths are white in color. After the adult lays her eggs on host plants, they hatch into caterpillars that feed on the foliage of the host tree.
  
  

Effects

• Bagworms feeding on evergreens cause the tree or shrub to have a ragged appearance. Evergreens that cannot grow new foliage quickly often die from heavy bagworm infestations. Bagworms place their bags on host tree limbs, leaving the bags only to feed. Female bagworms never leave their bags and die soon after laying eggs inside the bag.
  
  The gypsy moth caterpillar feeds for a period of 6 to 7 weeks before pupating. These caterpillars can cause significant damage to evergreens, but do not usually kill the host plant.
  
  

Cultural Control

• Removing caterpillars from your evergreens is one way to eliminate them. Hand-pick them from your evergreen and place the caterpillars inside a bucket filled with soapy water to destroy them. Caterpillars usually are actively feeding during the very early hours of the morning or just before dark. Remove the brown bags associated with bagworm infestations, as well. This is most effective if done before the eggs hatch in the spring. The larger caterpillars become, the more damage they cause and they are more difficult to control.
  
  A number of natural predatory insects feed on caterpillars, keeping their populations low, such as lady beetles and parasitic wasps. If predatory insects are present on your evergreens, it is important to avoid the use of chemical insecticides. These products kill the beneficial insects in addition to the caterpillars.
  
  

Chemical Control

• Caterpillars also can be controlled by applying insecticides on your evergreens. Choose a product with active ingredients, such as malathion, diazinon or acephate, for best results. Always follow the directions on the label for maximum effect and safety.