Did you try the Bt Lindsey? Don't want to sound like a broken record here but the stuff is great, and will only harm a caterpillar that actually takes a bite out of whatever plant you sprayed it on.
So if that guy is just some chance visitor that fell from a tree, and he doesn't find your orchids tasty he will simply be on his way. If he makes a meal of an orchid leaf, he will get sick and die, not live to lay eggs and cause further grief.
