I do use outside branches, but here's what I do. First, I bleach them. I use a mild bleach mixture, but it'll kill off anything that's not seen. After it's rinsed off really good, I bake the branch at 400 degrees for 10 minutes. That pretty much takes care of anything else in the piece of wood. After it's cooled, then it's ready for a snake cage. Just remember to have a REALLY secure lid. The more stuff that'll let a corn get to the top of the cage, the better chance they have of finding an opening. I actually had two corn snakes learn how to open critter cages! I now make my own cages, corn snake proof!
AJ