Alot of caterpillars are piosonous. I would not put it in with the BP.
Though, winter is pretty uch upon us now, and if the little guy hasn't spun a cocoon yet, I'd assume he will die off outdoors. If you really want to, put him in a jar or other container, and he might spin one. I kept some when I was a kid and it was pretty neat watching them morph into butterflies. But why would you wanna put it in with the snake!