Maggie, yes, BT is the thing for caterpillars. Had we caught indications of the infestation early enough, we would have used it, but the damage happened while we were away at a festival. The pond looked normal on Wednesday before Memorial Day, but when we next saw it the following Tuesday it had been eaten alive. Spraying at that point would have been pointless since we needed to get all the dead and damaged leaves out 'cause they were ugly.