How Do Mice Get Into a House?
"Mousie, mousie, mousie--stop nibbling on my housie! The problem is as old as human habitation. "If you can see one mouse," goes the old saying, "he's supporting another 10 that you can't." The common brown mouse and his cousins are remarkable survivors.
They are warm-blooded mammals that flourish in the coldest climates by moving in with their human neighbors, making themselves at home and helping themselves to any food left unattended.
Common house mice are tiny creatures, weighing about 1/2 oz. and measuring from 5 to 7 1/2 inches long, including their 3- to 4-inch long tail. The house mouse succeeds in areas where her larger cousin, the rat, cannot find enough food to support larger bodies and families. So, although mice do live in city buildings, they are more noticeable in suburbs and rural areas.
Since mice are warm-blooded, they look for shelter from winter's cold as soon as the weather starts to cool in the fall. Houses, barns or commercial buildings---anything that offers warmth and shelter will make a fine winter home. Mice search diligently until they find an opening. They can squeeze through tiny openings in foundations, ventilation stacks or siding. Occasionally, they can hitch a ride in decorations such as corn stalks that are brought indoors for autumn decor.
Once inside, your winter guests will build a nest with anything they can scrounge, including bits of draperies, furniture and cabinet doors. Once established, they will hunt for uncovered food constantly, mostly at night, to support their families. A female mouse can breed up to 10 times in her lifetime of 10-12 months and produce litters of five or six young per litter. They will search for grains---breakfast cereal, flour, oatmeal---or anything left out on the counter, unsealed or in a paper container (more nest material). Our grandmothers kept flour and other grains sealed in metal bins or lined drawers. We have the added choices of metal, ceramic or plastic canisters or containers. If mice can't find a ready source of food, they'll move on if it's early in the fall. Keep counters and cabinets especially clean and tidy during the summer and fall to discourage shoppers.
To encourage mice to settle elsewhere, remove the welcome mat. Caulk doors, windows, utility cable entries and foundation cracks. Use metal or concrete patch where possible. Find access points on upper floors of the house, too---mice can climb almost anything and jump over a foot. Stuff steel wool in larger openings and caulk in place. Use metal window screening to cover ventilation shafts and stacks that are not already secured. Since mice can squeeze in through a hole no larger than the diameter of a pencil, use metal screening, not chicken wire or mesh. Anything but metal will end up providing a foundation for nests.