Bagworms on an Evergreen Tree


Over 100 different species of trees such as arborvitaes, red cedar, junipers and blue spruces are known to have problems in urban areas when it comes to bagworm infestations. The case resembles a small cone-shaped bag hanging from the branches therefore giving the name of bagworm. The cone-shaped bag can grow to over six centimeters in length; it is tapered and open on both ends and made from silk and evergreen needles or leaves.


Life Cycle of Bagworms

Over winter, bagworms begin as eggs within bags fastened to twigs. These eggs hatch between mid-May and early June. After hatching, many of the caterpillars will release a stand of silk and are blown away to new trees, therefore spreading the infestation. The caterpillars then spin a protective bag around themselves and feed until late August or early September when the male will emerge and the female will deposit eggs before dying and the process begins over again.

The larva starts out as black and will eventually turn brown with yellow heads. An adult male bagworm resembles a bumble bee due to their transparent wings and hairy bodies. An adult female bagworm has yellow or cream colored body and resembles a maggot.

The Damage Caused

The damage caused by a bagworm infestation can be serious if left untreated. Bagworms thrive on leaves and buds of trees. The earliest signs of an infestation include stressed or browned needles at the end of branches. Severe infestations will lead to leaf loss that can lead to branch loss and eventually to death of the tree if protective measures are not taken. Less severe infestations will slow growth and stunt the plant.

Protection and Prevention

When noticing bagworms in fall, winter, or early spring (September through mid-April), there is not much that can be done other than hand picking the bags off the trees. In June, when the caterpillars emerge and begin feeding, insecticides can be sprayed to kill and prevent bagworms. These insecticides should be sprayed between late May and mid-June but may stretch as long as mid-August, but the sooner the better.

Natural remedies for bagworms include wasps which feed on and kill bagworms during the larva stage. One way to encourage wasps in areas with bagworm infestations is to plant flowering plants near infested trees. Flowering plants, such as asters and daisies, provide nectar and pollen to promote energy and egg development of wasps. Birds such as sparrows and finches are also natural enemies that can be coerced to the area with fruit and seed-baring plants and providing shrubs for roosting.

Sum it up

Insects, such as bagworms, can cause substantial damage to trees and shrubs that you have spent time and money on growing. An infestation can occur quickly and take the life of the tree or shrub even quicker. When caring for trees and shrubs, not all trees and shrubs are created equal. Research is the key for each particular plant being worked with. Lawn care services, tree service companies and nurseries are excellent resources to ask questions and get recommendations from.

If you are ever unsure of what to do, how to handle a job, or just too short on time it is best to call a professional to be sure the job is being done correctly. Look around, ask friends or family, and research companies on the Better Business Bureau to find a company that you can trust.

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