Gorilla zkittles

There is something you can spray for caterpillars larva and moth larva I can't seem to remember the name . BP I think. Please google that. If they are webbing themselves in they are pretty much water proof. So you have a couple of weeks while they pupate. They won't eat their nest. But you need to get them before they build a nest. Chuck.

I would look at neem oil. It's not good at removing an infestation but it's pretty good at preventing them. But since you are dealing with a large insect I would give my plant a good inspection every day and manually remove any buggers.