How to Introduce Two Pet Mice to the Same Cage
Pet stores like to confuse mouse owners. Nearly every store I've visited has a little card or plaque that says, "Mice are social animals and get depressed without other mice." However, every time I've tried to buy two mice--especially male mice--the pet store worker will tell me, "If you get two, they'll fight." Advice like this makes it hard to make the right decision for your would-be pets.
While it seems contradictory, however, both of these statements are true. Mice will fight, but they like the company of other mice. They have instinctual issues to resolve—mostly male mice, and for the rest of the article I will discuss male mice unless otherwise noted—and that can lead to fighting and sometimes bloodshed.
The easiest way to keep multiple mice in one cage is to buy them young, preferably from the same litter, and buy them all together. Mice who live together as children—such as Sasuke and Gaara—tend to cohabitate as adults better than mice who don't know each other. Furthermore, we introduced two children to one adult, which initially gave Hannibal the edge in becoming the alpha mouse, which turned out to be a mistake. Mice fight for dominance and generally accept the chain of command once they establish it. When Sasuke grew up, though, he had a stronger alpha-mouse behavior, and challenging Hannibal for the position turned bloody.
Therefore, I recommend introducing mice before they've all matured, or after they've all grown completely. Introducing animals at mixed stages of development might not help in the long run.
But you may find that you can't do that. Pet stores usually sell children and adolescent mice exclusively. We could have waited until Gaara and Sasuke had matured, but we didn't quite have the experience to know better.
Either way, here are some techniques we tried, and I'll note how effective we suspect it was. To start, this is a list of things you need.
- At least one cage for every mouse, even if you only have small travel cages
- A box with very tall sides, preferably plastic but thick cardboard works too.
- Fresh bedding
- A few tubes and small boxes to give them personal space if they want it.
Introduce Them on Neutral Ground
Mice claim territory. Throwing new mice into a pre-marked cage will start a fight. Instead, place them all together in a box. Mice jump and climb, especially young ones. Make sure the sides are about two feet tall and smooth. If the water bottle gets them high enough to jump out, stick it in a corner and put a sheet of cardboard over the top of that part of the box.
No one has marked the box. Without territory disputes, the mice probably will be more interested in each other.
Wipe Their Haunches With Vanilla
Vanilla overpowers the individual scents of each mouse. If all the mice smell identical, we've been told, they will accept each other as friends.
We did this. It may have helped. It certainly didn't hurt. What we saw, though, was three mice spending twenty minutes wiping vanilla off their fur, then sniffing around each other. Each attempt we made to introduce them with vanilla failed. This is only one case, however, so I wouldn't rule out the option completely.
Wait Until Just Before Their Bedtime
If you've had at least one mouse for any amount of time, you should know its sleep patterns. Most mice sleep during the day, so if you drop them in the box in the morning, they may be too tired to care about strange mice. But unlike the vanilla, this forces them to do something together. If they don't know each other (and even if they hate each other), mice will sleep together for warmth. Our mice seemed to bond over it.
Tolerate Little Squabbles
When you put them together, they will prioritize the establishment of a hierarchy. You will hear squeaking, and you'll probably see a good deal of male-on-male mounting. Just let it slide. The subordinate mice don't like it, but it doesn't hurt them and they need to resolve who's the king. (The alpha mouse seems to be responsible for grooming the others and for building the nest. Dominance doesn't indicate a tyrannical mouse.)
Pay close attention, though, to see that they're working out the pecking order and not fighting legitimately.
Be Patient and Persistent
We tried introducing these mice on three separate weekends. The first two failed miserably and we gave up. Hannibal went back to living alone and Gaara and Sasuke moved into the new cage together. After a few days, however, I noticed Gaara--a generally laid-back mouse--started picking on Sasuke. It annoyed me, but rather than split them up I wondered what introducing the more aggressive alpha male would do. For some reason, when I stuck them back in the box with Hannibal, they began to play nice with each other.
Give It Time
One source told us that if they didn't fight within the first hour, they probably wouldn't fight at all. Not true.
Leave them in the box for at least 24 hours. Watch them closely--I had to keep the box by my bed. If they still seem cool with each other after a day or two, you can put them in a cage together.
Housing Them Together
At this point, you should still have one cage for each mouse. If you own three or more, get at least two that connect. An average cage should house a maximum of two mice. So if you have a lot of mice, make sure a lot of cages can be strung together. Mice need space.
This part is tricky. You already had one mouse living in one of the cages. Before putting your new mice in with him, clean it thoroughly. You don't want any scent lingering to suggest anyone still owns the territory. If at all possible, though, change the layout of the cage. This will make the first mouse feel like he's moved into a new place, even if he remembers his home. If one cage is new--which at least one should be, since you need one cage for each mouse--put them in that one. They'll make their way to the other soon enough, but the more unfamiliar they are with the cage, the less likely they are to fight over it.
Don't Assume You're Done
Even if they accept each other now, they may find good reason to fight each other later. After all, we've all had bad roommates. I had one who piled trash in his room, never showered, stole from me, and ate my food. After he ate most of a cake I baked, I injected laxatives into the last piece and let him have it.
Mice don't often have access to laxatives, so they probably will just fight to the death.
Hannibal, Sasuke and Gaara lived together as friends for about two months with nothing more than a few minor squabbles. Then one day, Sasuke had had his fill of being dominated, fought back, and injured Hannibal pretty badly. They both survived, but we couldn't bring them anywhere near each other ever again. They had to live in separate cages and we couldn't take them out at the same time.
While this is our story, I can't claim that this will apply to any mouse you bring home. These animals resemble humans, and therefore have a complex psychology. Just use our experience as a guideline and be prepared for failure. If you have success, though, drop a comment and let me know what you did.
Know Your Alpha Mouse
Since writing this article, we've had a number of mice come and go, and I noticed an interesting trend among housing male mice together. As mentioned above, the three mice in the picture lived in relative harmony until Sasuke grew into adulthood and became the alpha mouse of the group. We had to separate him. Sasuke went to live on his own, while Hannibal and Gaara lived the rest of their lives together with not even the smallest squabble.
When Hannibal and Gaara died, we bought two female mice to replace them, and since one of them turned out to be pregnant, we ended up with three more mice. We let Sasuke stay in a cage on his own, while the girls got one cage and the boys, Sean Bean and Jon Snow, lived together.
The two brothers lived together with a reasonable amount of discord--as you'd expect among siblings--but interacted very well most of the time. Then when Sasuke passed away, things started changing. Sean Bean became more aggressive and territorial. When the fights got worse and Sean Bean terrified Jon Snow into spending all his time in a small corner of the cage--away from the food and water--we separated them.
Test this at your own risk, and always keep a close watch over male mice living together, but I suspect male mice can live together peacefully as long as the alpha of the group is separated, but living nearby. Sasuke's death, even though they never interacted, left the room without the scent (or so I assume) of an alpha mouse, and one of the others had to take that place. Leave a comment if you try this; I want to know if it works for other people.
This article is accurate and true to the best of the author’s knowledge. It is not meant to substitute for diagnosis, prognosis, treatment, prescription, or formal and individualized advice from a veterinary medical professional. Animals exhibiting signs and symptoms of distress should be seen by a veterinarian immediately.