The following is my response to a question I got about rat aggression. I decided to post my response publicly because I get this question a lot and I think it is a pretty common problem among pet rat owners. For more information about rat adoption gone wrong, see my previous post, “Oh, no! I adopted some new rats and now they are sick/mean…etc!”
Question: My rat has started biting me and bullying her cage mates, what can I do?
This question comes from a person who has a female rat that has started biting it’s owner and attacking and wounding it’s cage mates. The owner says that the rat is healthy and nothing has changed in it’s environment to cause the change in behavior. They want to know what to do about this aggressive behavior.
I am sorry you are having this problem. First let me say that there are two possible reasons a healthy rat may become aggressive. One is that they have become afraid for some reason, some change occurred. Something happened… maybe they were attacked by a cage mate, were mistreated by someone in the home, they simply stopped being handled for a while, or you got a new pet or a new cage and they felt more vulnerable by the extra space. If something happened to traumatize the rat (even if it doesn’t seem traumatic to you), you can usually help it return to it’s friendly demeanor by addressing the problem and doing some trust training to help it feel safe again. The other really common reason for rat aggression is poor temperament. This is mainly caused by bad breeding, and I hate to be the bearer of bad news, but this kind of rat aggression can be really hard to deal with and often people end up having to put aggressive rats to sleep because of how bad it can get for the people and the other rats around them.
Bad temperament is usually seen in aggressive behavior that has no cause. No new rats or pets were brought home, not sick, not pregnant, no new cage, no new trauma of any kind occurred, but the otherwise healthy rat has become “mean”. Hormonal aggression also falls under this category and should have been bred out of the line. For male rats, having them fixed is one way to try to remedy hormonal aggression. Usually the fixed male can then be integrated into a colony of females and can do very well. Unfortunately the same is not a practical option for hormonally aggressive females. One way you can try to determine if it could be a problem of bad temperament, is to know where the rat originally was bred and to find out if the rat had to be actively socialized as a baby (meaning it had to be handled constantly or it became skittish or bitey) in order to act friendly to humans. This early socialization often just helps rats be unafraid of humans and is a helpful practice, but it also can have masked a natural inclination toward aggression or dominance, which is something a good breeder would have actively bred out of their lines before offering any rats to the public. This type of aggression can be extremely hard to deal with and usually just gets worse over time. Poor temperament is usually seen in feeder bin rats, pet store rats and “oops” litters bred by uninformed pet owners. If temperament is the problem, then there is nothing that will work for long. There are a few very good breeders who actually temperament test their rats before offering them for adoption. Most just handle the babies a lot in the beginning, which socializes them, but doesn’t reveal much about their given tendencies, so some of this behavior can pop up unexpectedly after the rat has fully matured.
Sometimes friendly rats become skittish after being put into a new cage or a huge cage. You may feel like you are giving them a wonderful amount of space to run and play in, but rats are prey animals and they like to hide to feel secure. A huge somewhat empty space can make them feel vulnerable and affect their behavior. Have you felt that kind of creepy/foreboding feeling you can get when you stand alone in a big empty or unfamiliar house? I have, especially when house sitting or when I have looked at houses with a realtor. If that can feel disturbing to us, then how much more disturbing to a prey animal that is hardwired to run and hide? The ideal solution is to really clutter up the space with lots of cubes, hammocks, and hides to help them feel more secure. If that doesn’t work, return them to the smaller cage and work on trust training or re-socializing them. They should be back to their normal selves fairly quickly.
That being said, if a rat is naturally friendly, but just got a little scared or wasn’t handled enough you can try trust training methods to get the rat to stop acting out and start trusting again. Here are some links for dealing with aggression that might give you some ideas of what you can try. Hopefully it is not a temperament problem and you can help your rat return to the once friendly pet she was. Good luck!