I've checked more than twice, I keep thinking that. But they haven't tried mounting each other and I'm not an expert but they look the same and the woman who I bought them from told me they were female also. I even checked their genitalia with my mom's female guinea pigs and they all look the same. I need to get them a bigger cage, but they do it outside the cage also. I'm thinking it's from the lack of space that I am going to fix very soon, but I didn't know.