Tent caterpillars form huge, weblike nests in many trees and shrubs. They venture out during the day to feed,then return to their nests each night. Bad infestations can defoliate entire trees.
The most effective control is to cut off the limb containing the nest; do so at dusk, when more caterpillars are home for the evening. If removing an infested limb would seriously deform the plant, break up the nest with a stick and spray the inside with Bt. Handpick sticky egg masses from plants in late winter and early spring. Wrap plant trunks with sticky barriers to keep pregnant females from climbing up to lay eggs.
Carbaryl, diazinon, and malathion are effective chemical controls against caterpillars.