 you stop eating immediately. And usually that caterpillar will die, not from the spray, but just from starvation. They just get sick to their stomach and they stop eating and they just drop, they vaporize. It's very gratifying as a gardener. If you want to take out caterpillars, that's a good way to do it. BT, it's a liquid. You spray the flowers, the foliage. It doesn't matter if you hit the caterpillar, just spray the flowers. They're going to come out in the morning.