Aggressive mouse

Question
HI Tamarah,
I bought a beautiful mouse from a pet store because we have no breeders where I live. She's a satin Angora Siamese but she's horribly aggressive and I am confused why and what I can do. She bites me everytime she comes near my hand, if my hand is in the cage she pushes piles of bedding of it and when I am near the cage she slaps her tail on the side. She squints her eyes when she smells me nearby and I always use unscented soap. She also scratches me if she doesn't bite. I wonder if maybe she's pregnant because I read mice typically aren't aggressive - more prone to hiding and being fearful. She made a nest under a structure I have and literally used everything I put in the cage to make it and she spends a lot of time in it during the evenings but she is not pear shaped and I don't think she barbered her nipples but I can't tell much because of course I can't even touch her.
I actually feel afraid to try to interact with her now.
Also, the employee didnt give me a proper age she said she thought the mice were 5 months old but I dont know if thats reliable being that she seemed confused. I can tell the mouse is fully grown however.

Answer
Hi Charlotte,

How long have you had her?  Mice are very prone to skittishness when they first come home, and I'd give her a couple of weeks to adjust before worrying too much.  She will need a little time to settle in and understand that her new home isn't a scary place.

It's not necessarily the case that she is pregnant, although if she was housed with males it is absolutely possible.  Some mice are more anxious and/or aggressive than others, especially if they were not handled sufficiently as babies or were bred from particularly anxious parents.

If it has been a couple of weeks already, and she is still biting you and acting terrified whenever you are near, you have two choices - either return the mouse and get a calmer one more suited to your home, or try to train her into better behavior.  Consider how willing you are to take a long time, possibly months, to work with her.  If you are already scared of her, that will affect how successful your training will be.  There's nothing wrong with making an exchange, so that she can go to a home that has less interaction.

If you decide to keep her, the first thing I would do is get a good pair of heavy gloves that she cannot bite through.  This will allow you to keep your hand steady if she nips at the gloves, so you don't reinforce her behavior by yanking your hand away and showing her that biting successfully gets rid of you!  The next thing I would do is consider her environment.  Where is her cage placed?  If it is in an environment with a lot of foot traffic besides you, such as guests or family members, consider moving it to somewhere less stressful.  If it is in a place where you only go once or twice a day, try moving it to somewhere you are frequently, so she can get used to you being present in a nonthreatening manner.

Make every interaction with her both nonthreatening and positive.  Do this by visiting her cage a couple of times a day and placing your gloved hand in during a time when she is already awake and active.  You can either do something simple like refill her food or water, or simply leave your hand in there for a few moments.  You want her to come up and sniff you eventually, but not bite (it's okay if she doesn't come up, don't reach for her).  If she does bite, don't flinch or remove your hand until she has backed off and away.  Until her body language becomes more relaxed and she sniffs you, don't reach to pet or touch her.  You're just letting her get used to your smell at first.  After each visit, and any time she comes up to the side of the cage to show relaxed interest in you, reward her with a treat - simply drop it in the cage afterwards and then retreat.  Remember that the calmer you are, the calmer she will be.

Obviously you will have to clean her cage at some point.  The easiest way to do this without traumatizing either of you will be to use a toy or hide.  Wait until she crawls in, then lift the entire hide out, covering exits, and place into a secure "waiting area" (like another cage).  Then change the cage, adding a little dirty bedding so it smells familiar.  Replace all her toys/hides where they were before, and then repeat the process to get her back into the cage.  Then leave and let her rearrange it!  If you've been chasing her for a while and can't get her out of the cage, leave and try again at another time.  Again, we want every interaction to end positively and incur as little stress as possible.

Again, however, it's completely okay to say, "no, this mouse isn't a good fit for me."  It's just a decision you'll have to make for yourself, since you know her better than I do!  I just hate to see both of you stressed out when having a mouse should be fun!

Please let me know if there is anything else you have questions about, and I'll do my best to help out.

-Tam