The first is clipping and then destroying the webs. You clip between October and early April. After you clip, do not leave the web on the ground or some caterpillars will survive. You can carefully burn the webs or you can soak the clipped webs in water with detergent added The second way is to use Dimilin spray, but it is harmful to lobsters and other shellfish. The pesticide acts by blocking the formation of chitin, a tough substance that gives the body of the caterpillar its structure.
Chitin is the same thing of which lobster and shellfish shells are made.
Dimilin spray should only be used as a last resort by homeowners with high numbers of caterpillars. The spray is effective in May and early June when the moths are in the caterpillar stage. Bt, another spray, is found in the soil in nature, but not in sufficient quantity to kill an epidemic of caterpillars. Bt has been around for decades. It was first registered as a pesticide in 1954.