Mice can breed incredibly fast, especially when they’re sheltering in your home. In the wild, a mouse has an average lifespan of just 12 months, but this rises to two or three years when they have the benefit of the security that your home provides. The availability of food and shelter are the main limiting factors on the rate at which mice breed. If they have limitless access to both of these vital resources, female mice can get pregnant from five to ten days every year. They have an average gestation period of 19 to 21 days each time they get pregnant and produce a litter of between six and eight pups.
These numbers mean that each female mouse can produce between 32 and 56 pups each year, roughly half of which will be female. As soon as they give birth, female mice are ready to mate again; they reach reproductive maturity after just six weeks. A breeding pair of mice can potentially spawn thousands of pups in each 12 month period.
When they establish their nests in people’s homes, mice continue to reproduce until they reach their environment’s resource limit. The resource limit is determined by the space available and their access to food. The more space and food available, the more mice the environment can support.
Because mice breed so quickly, even a single pair in your home can soon become a significant issue. As soon as they have built their nests, adult mice will start reproducing and won’t stop until they have to.