The first egg masses of eastern tent caterpillar are hatching in northern Illinois, and many of the egg clusters have now hatched in southern and central Illinois. They appear as white silk tents 1 to 3 inches across in the branch crotches of crabapple, hawthorn, mountain ash, flowering cherry, and other trees and shrubs in the rose family.
At this time of year, it is easy to just pull out the silk tent and associated 1/2-inch-long dark caterpillars by hand. Dispose of them at a generous distance from the tree. When they are this small, they spend most of their time in the silk tent, but all are in the silk tent on cloudy or rainy days as well as at night. Sprays of Bacillus thuringiensis kurstaki (Dipel, Thuricide) and other chemical insecticides are also effective.