I kept pretty much everything I used to have in pairs or more, but this was when I didnt know very much about reptiles. I used to have a small group of corns together, a pair of Grey/Black rats, trio of royals and 2 young burms together. I never experienced any problems at all. Except as Ryan says, mites were an issue. They got introduced somehow and the whole collection got infested...wasnt very happy...:lol:
Now I only keep a pair of Blue Beauties together, but they are being separated soon as I find it much easier to look after them and monitor them when they are on their own. :lol: :lol: