I don't know, I know that caterpillars love to eat leaves and other foliage, na? Well, if he hasn't eaten or ruined but one leaf, I'd say let him stay; not very stoner-love-riffic if you kill the lil guy for doing what's in his nature.

But if he does start to cause harm to your plantage, than I would say just pick him up and lay him on a leaf on a tree outside, and remember to thank him for thinking your plant was worthy and vacation-y enough to nest in.