Bagworm caterpillars are pests that defoliate and eventually damage a tree if not eliminated. The worms are commonly found on conifer species; however, it is possible for a deciduous tree to become infected. Bagworms are slow-moving pests; they do not jump quickly from one tree to another because the queen is unable to fly. This makes it possible to remove bagworms, without the use of pesticides, by manually pulling off the egg sacks that form in early summer.
The bagworm caterpillar mates with the wingless female in a sack made from parts of the tree. The sacks are about 2 inches long with a cone shape that is large on top and tapers toward the bottom. Bagworm sacks on a conifer tree have the appearance of a small pine cone with needles protruding from the side. They are made from silk and bits of matter from the host tree. The egg sacks form in early June and remain on the tree for about four weeks before they hatch.
The first step in removing bagworms is inspecting the tree to check for egg sacks. Walk around the perimeter of the tree and look inside the branches, toward the trunk of the tree to verify the growths on the tree are from bagworms. Take a second look at the tree after removal of the egg sacks to verify they are all gone. While the pest does not move quickly to other trees, inspect all of the surrounding trees to verify the worms did not spread.
Remove all visible bags from the tree by picking them with your hands or clipping them with pruning shears and placing them into a garbage bag. Remove all egg sacks found the infected tree and any surrounding trees that are infected. Destroy the egg sacks by tying the bag and throwing it in the trash, or burning. Repeat the removal of bagworm sacks that appear on the tree the following season to prevent the hatching of eggs and introducing more worms to the environment.
Consider a chemical pesticide if manually removing the egg sacks for two seasons does not control the problem. Apply a pesticide in early spring to kill the worms when they are active and prevent them from making egg sacks that may hatch in late summer.