The tent-making caterpillars have many natural enemies such as hunting wasps, birds, and predaceous bugs. Wasps and flies prey on caterpillars as well. Tent caterpillars are vulnerable to diseases as well. Because of these controls, any outbreaks of tent worms last usually no longer than a season. An exception to this is the fall webworm and the reason it has been spreading is due to the increased spraying of mosquitos.
Contact insecticides are effective for tent-making caterpillars as well. Sevin has been available for awhile. Insecticides such as cyfluthrin, permethrin, and esfenvalerate are effective for homeowner application and are very effective.