Milk, rat, and king snakes are all cannibals - they will kill and eat other snakes. This is why I get upset when my neighbors kill the wild black rat snakes - they are killing a snake that eats copperheads and rattlesnakes.
The husbandry requirements for the milk snakes are vastly different than for the BP. The milk needs temps from the low-mid 70's to mid 80's with low to moderate humidity, your ball python needs temps from the upper 70's to low 90's with high humidity.
