Please help my little mice!

Question
QUESTION: Hi. I have had my little female albino mouse (Bella) for about one and a half years now and she lives in a normal plastic cage. Just yesterday, i went and unexpectedly bought another mouse. She is a girl (named Binkie) and is only four weeks old (so cute!) and she seems to get along with Bella but sometimes when i am watching them, i hear loud sharp squeaks and i have never heard that before, and i thought it would be Binkie but when i watched closely, Bella would suddenly jolt her body (which i think means she is squeaking) and Binkie is right next to her when she does it. I love them both so much but i dont want Bella to get hurt. I also just noticed a tiny dot of blood under Bella's eye and i dont remember that being there before. Please help. I dont want to give Binkie back and i cant afford to separate them.

ANSWER: Females don't usually fight and usually it's older females who will bully younger females. This of course doesn't mean that Binky is not the problem. If there aren't any serious injuries, you don't need to separate your mice, they're just figuring out their new places in each other's lives. Once a mouse has secured their niche then the fighting will stop, for males this is different but you have females so there is no problem. The fact that Bella is squeaking when Binkie comes near her could merely be because she was so used to being alone and now she has a little girl poking and prodding at her so she squeaks her dislike. It's like a forty something woman being constantly annoyed by a ten year old girl. You can't train them to act differently like you would a dog so there's nothing you can do besides separating the two but I assure you that this will most likely not be necessary, let them figure each other out and soon they'll be the best of buddies and they'll sleep together, play, and eat together. It usually takes my mice about two to three weeks to get used to a new companion.

---------- FOLLOW-UP ----------

QUESTION: thank you! Binkie is nicer and they sleep together all the time and they love
eachother loads now! Just one more question... since i got Binkie, Bella's fur
on her back (the area that should be cleaned by a drop of water, the place
mice can't reach) is all clumpy like it is damp. I was wondering if that is
normal. im not very worried as i have a feeling its just because Binkie licks it
there to help Bella get clean but i just need to know if its something i need to
worry about?

Answer
Well I'm glad Binkie improved and the matted fur on Bella's back could be caused by two things, Binkie is grooming her there, like you suggested, or there may be some over grooming going on. Watch for thinning patches of hair or bald spots on Bella, if they appear it would be best to separate them. Although over grooming won't always cause too much of a problem, sometimes mice will gnaw off the other mouse's entire ear. Just keep an eye on them and if you see that Bella is starting to look really bad I would suggest removing Binkie.