If you aren't too sure what you are looking at, it could just be his testicles you are seeing and not exactly his butt. They are sometimes more swollen from one day to the next, so if they look bigger than normal, it's nothing to worry about. He is probably just producing too much sperm … Read more

Those are the hamster's testicles, not his butt. Nothing to worry about. Male hamsters have very large ones. I know, because I have one and his are huge, but that's normal! :)