Gypsy moth larvae emerge from the egg cases from mid May through early June. Some people have reported success spraying the larvae with Seven - an insecticide available at most garden centers. Always follow the label instructions when spraying any insecticide or herbicide!
If you observe large numbers of caterpillars on a tree, wrap a burlap bag loosely around the trunk of the tree, about chest high. At night the caterpillars move down the trees and will hide in the burlap to escape nighttime predators. Remember: Every caterpillar that reaches maturity will produce between 200 and 600 eggs toward next year’s hatch!
For more information about gypsy moth control visit: http://gypsymoth.wi.gov/,or contact the Wisconsin Department of Natural Resources at 1-800-642-MOTH or the Greendale Department of Public Works at (414) 423-2133.