I have had a female russian for about 5-6 months, we just got a new one, we are pretty sure it's another female, but it's hard to tell because it's pretty young. The past couple days our old one, which is probably like 5 years older and quite a bit bigger is bullying the younger one. It keeps trying to bite the legs of the little one. The bite is pretty hard, I've taken one in the finger and it seems like it could do some damage to the little ones legs. Is this common? What should I do?