It's odd that I came across this thread for the first time just now.
Odd, because I just found a rat snake in my sun room this morning. The "sun room" was previously a deck, which has been enclosed well enough that I keep my tropical plants out there in the winter, and it also houses my cage birds and one cage of bantam cochins -- but when the weather is warm, the windows are all open with welded wire over them to keep the dogs out. So, in warm weather, it's really only semi-enclosed.
Anyway -- I found the rat snake out there this morning. I bid him good luck in his mouse hunting chores, and I let him go about his slithery way. My cochins are too big for him, my small chicks are in enclosed brooders in the house, my cage birds are in snake-proof cages, and if he eats an egg or two it's worth the price.
I was very happy to see him. I've got lots of animals so I'm not going to be using poison, and I need all the help I can get with rodent control!