The Rat Fan Club

Introducing New Rats

by Debbie “The Rat Lady” Ducommun

updated 1/18/16

The willingness of rats to accept a new roommate depends on their personality and age. It will take more time—sometimes up to several weeks—to introduce a newcomer to adult rats, but it can be done. With time and patience, almost any rat will accept a newcomer. However, there are a few rats, typically from pet shops with poor breeding, that can genetically aggressive who will need to be spayed or neutered before they will get along with other rats. And I have known some very aggressive males who still won’t accept other rats even when neutered. But these are the exceptions.

The introduction process has several steps and the time required for each may vary. The easiest pairing will be two young rats, while the most difficult introduction is between two adult males, especially if they aren’t neutered. On the other hand, as rats start to age they can mellow out and be more accepting of new roommates. A young rat is the best choice for a new roommate for an adult male, but the newcomer should be at least six weeks old. This is because adult males will sometimes kill strange baby rats younger than this.

When introducing rats, you should have two cages so the new rat can have his own cage at first. (The second cage can be the resident rat's travel cage.) Never just plop a new rat in the resident rats’ cage because the residents will always defend their territory.

During the introduction process, you should only advance to the next step if there is no sign of aggression within 30 minutes. A resident rat will express aggression by puffing up his fur, arching his back, and swinging his body sideways at the newcomer. If you see this type of behavior, remove the new rat quickly to prevent an attack. Use care when picking up an aggressive rat as they will sometimes bite. Pick them up with a towel. Or if need to quickly break up a fight, you can pick up the aggressor by the base of his tail. If an introductory session results in aggression, try again later, or go back a step. Introducing hairless or rex rats can take extra care because they won’t b able to show you the puffed fur of aggression.

When introducing a new rat to a group of rats, usually only the dominant resident rat will be aggressive toward the newcomer at first. This is the dominant rat’s “job.” Once the new rat is accepted by the dominant rat, the others may show some aggression in turn, but it usually won’t be as severe.

The Introduction Process

The first step is to place the cages near each other so the rats can see and smell each other. Place wire cages far enough apart so the rats can’t reach through the bars to the other cage, or the result may be bitten toes or tail. The next step is to switch the rats to each other’s cage, even briefly. This allows them first-hand experience with each other’s scent. You may have to do this several times.

The next step is to introduce the rats in neutral territory, which should be someplace where the resident rats are not used to playing. The bathtub is a good place. This will give them a chance to become acquainted without the residents feeling the need to defend their territory.

The next step is to let them interact in an area where the residents are used to playing. Watch them carefully, because this is where some fighting may break out. It may also help if you put the new rat(s) in your lap along with the other rats. By holding everyone at the same time, it may let the residents know that YOU have already accepted the new rat.

If one of the residents persists in being aggressive toward a new rat, be sure you let the resident know that you are displeased with this behavior. Tell him or her, “No,” in a firm voice, and “be nice, I want you to get along.”  If the aggressive behavior persists, try tapping the aggressive rat on the head firmly. You can also try immediately returning the aggressor to his or her cage for unwanted behavior.

When the rats can get along in the play area for at least 30 minutes without aggression, you can go to the final step. Clean out the larger cage completely and rearrange the furnishings so it appears to be a new cage. Trim the back toenails of the rats to minimize scratching in a scuffle. Put vanilla extract or perfume on all the rats to make them smell the same. Then put the rats in this cage. The best time to do this is in the morning when rats tend to be sleepy.

The dominant resident will probably sniff the newcomer and then pounce on him, forcing him over on his back. If you’ve followed the introduction process correctly, don’t rush to take the new rat out. Instead, carefully observe the behavior. Observe whether the resident rat is showing the raised hair, arched back, and sideways approach that are signs of aggression. If so, remove the newcomer, but if not, leave them together. The resident rat must establish his or her dominance and it’s normal for them to “beat up” the newcomer. Just because the new rat is squeaking doesn’t mean it’s getting hurt. This is just a rat’s way of saying “I give up.” As long as you have followed the introduction process step by step, and as long as the resident rat isn’t showing the signs of aggression, you should let the fight run its course. If you take the new rat out, you’ll prolong this adjustment phase.

However, if it appears that the new rat is being injured, or if the attack seems especially vicious, then of course you should remove him from the cage. But in most cases the “fight” will be over quickly. The dominant resident rat will probably beat up the newcomer frequently for the first few days, and you shouldn’t interfere as long as there are no injuries. But the first attack is usually the worst, and before long the rats will typically become the best of friends, sleeping together and grooming each other.

One of my members also suggested something that worked well for her. She smeared all her rats with pudding! After they got it all licked off each other, they had bonded! But this was a group of rats who had lived in the same house for a while, not brand new rats. You would still need to go through all they preliminary steps first.

Because rats are individuals with their own personalities, occasionally two rats will take a dislike to each other and constantly fight. In some cases, this means the pecking order is changing and the fighting will stop eventually. Neutering any males involved will usually solve the problem. (After a male is neutered, it can take up to 8 weeks for their behavior to change.) However, if these fights continue for more than several weeks, such rats should be separated permanently.

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