WHATS GOING ON? The male mouse is aggressive

[Bogertophis]

I've raised mice for many years (still do), & sometimes one of my male mice becomes aggressive with females, usually with previously unknown females, but not always.

Often it's right after cage cleaning- bear in mind that mice know each other by scent, & when that changes, that can cause the sudden aggression to what is perceived as
an "outsider". (I'm assuming your mice are correctly sexed.) BTW, the male mice have most of the odor, which is rubbed off onto their females & offspring...keep this in
mind if you raise more mice & wish to mix them up so they aren't inbred. Males may also attack babies from another litter if you aren't careful (like if you try to even up litters so they all get fed...some litters are too many for one mom to feed).

Sometimes a distraction* will help smooth things over: a food treat (like sunflower seeds, peanuts, mealworms) may distract the male long enough for all the mice to once again "smell the same". It also helps to put some of their litter over them to do the same thing...help them smell the same as each other. *Gerbils are even WORSE about "outsiders" (though either mouse or gerbils may kill other males) & years ago when I had some gerbils, I successfully got them to accept each other by putting them in acontainer with some clean dirt to dig in (something they love to do) & in short order, they all smelled like the dirt, & became a "family unit" instead of going to war.

When that fails, even some males that were previously good breeders & peaceful...the hyper-aggressive male becomes dinner to one of my snakes & another male moves
up to the rank of breeder...at which point, sometimes the females go after HIM because they don't "know" him.... Mice! You can always order frozen...LOL

If you only have one snake to feed, or even a couple, it's not cost-effective to breed your own rodents, plus you'll end up with too many.

And the short answer is, some male mice are just jerks. LOL