Q&A: Do bagworms kill trees?

Bagwoom cocoon

Bagworm cases are made with evergreen needles and leaf material

Q: Do bagworms kill trees?

A: If there is a large infestation of bagworms on an evergreen tree, it is indeed possible for them to kill the tree if the defoliation is severe. Bagworms can be a problem on deciduous trees as well, but they typically do not kill them.

Bagworms are a common pest in Maryland and we receive a lot of questions about how to deal with them. Fall and winter are the best time to remove and destroy the bags that contain the eggs.

Here are a few tips about the lifecycle of bagworms and how to control them.

Bagworm Basics

  • Bagworms are most commonly found on evergreen trees such as junipers, cedars, and arborvitae, but they feed on a variety of other trees and shrubs as well.
  • Bagworm eggs hatch in late May or early June. Young caterpillars spin a cocoon-like bag to which they attach pieces of leaves or needles of the plants they are feeding on. The caterpillars grow and feed all summer and the bags expand with them.
  • Bagworm caterpillars pupate in late summer. Then adult male moths emerge and fly to bags containing wingless female moths. After mating, the female lays 200-1,000 eggs in the bag and dies. Eggs overwinter in the female bag.

How to Control Bagworms

  • In fall and winter, remove and destroy bags containing the overwintering eggs of bagworms. The bags are attached tightly to branches, so you may need small clippers to cut them off. Put them in the trash.
  • In the spring – late May to early June – look for the small bags forming on plants, especially on evergreens. An ideal time to control bagworms is in early June when the young caterpillars are small and beginning to make their cocoons.
  • Infested plants can be sprayed with B.t. (Bacillus thuringiensis) to kill the young caterpillars.

Learn more about bagworms and other common landscape insects on the Home & Garden Information Center website.

Have a question about tree and shrub care? Submit your question to Ask an Expert.

By Mary Kay Malinoski, Extension Specialist, University of Maryland Extension, Home & Garden Information Center

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