i have been feeding my snakes pinky mice from the local petstores, and i want to go over to rats. but now i am reading hoppers, crawlers, pinkies, and other terms.. what is what. i have always fed mice that were as large as the largest section of the snakes body girth. should i bump it up, or leave it alone. can i start feeding rats now? i assume roswell is at least 6 months, and he is about 20" long. i havent attempted the girth measurement yet. any kind of rats would do? i know there are a few kinds of rats they sell. i think they are all just rats to me.