The Maine Department of Agriculture, Conservation and Forestry’s Maine Forest Service will release the flies on Wednesday in Bath. The service says the flies only attack the moths, and have been successfully used to control the moths in Canada and New England.

The winter moth is originally from Europe. Their larvae feed on the leaves of trees and shrubs, some of which yield important Maine products such as maple and blueberries.

The flies are in cocoons for the winter and will be placed in a cage that is buried in the ground. The cage will be opened in early May.