About Bagworms

Geography

• Approximately 600 species of bagworms are found throughout the world. In the United States, the common bagworm (Thyridopteryx ephemeraeformis) lives primarily in the eastern and southeastern parts of the country. Bagworms are a problem for citrus growers in Florida, and also cause considerable damage to evergreen trees throughout the eastern U.S.

Identification

• Bagworms are rarely seen without their bag and are often hidden inside. The bags are generally 1 to 2 1/2 inches long and spindle-shaped. They are covered with dried plant debris, such as pine needles, dead leaves, strips of bark and twigs. Bags may be seen hanging from a tree branch, or moving slowly on the tree's trunk or limbs. They are sometimes difficult to spot; the bags are well-camouflaged. This is especially true when bagworms have infested a conifer, since the bag may resemble a pine cone.

Misconceptions

• Bagworms are frequently confused with another common pest--tentworms. Tentworms form large webbed "tents" that span multiple branches and are often quite unsightly. Unlike bagworms, tentworm infestations are clearly visible; the caterpillars live in colonies, and only deciduous trees are affected. Both types of caterpillars can cause serious damage to trees.

Type

• The common bagworm is the most well-known in the United States. This bagworm infests many different types of evergreen and deciduous trees, including oak, birch, pine, cedar, apple and orange. Grass bagworms are sometimes spotted hanging from fences surrounding pasture land. They are much smaller than common bagworms and do no damage. Snailcase bagworms live in round, coiled cases that are often attached to buildings. They cause only minor harm to plants, but the cases frequently damage manmade surfaces they adhere to.

Effects

• Common bagworms are voracious feeders and quickly strip the leaves from trees. A serious bagworm infestation may completely defoliate the host tree. The bags often go unnoticed until extensive damage has taken place and the tree dies as a result. Controlling bagworm populations can help prevent the death of trees and reduce losses for growers. In minor cases, bagworm control consists of handpicking the bags from the trees; when the infestation is heavy, pesticides are often required.