Mice living in your walls can eat through the electrical wiring, contaminate the insulation and gnaw holes in the framing. They will also probably steal uncovered food in your kitchen or pantry, leaving trails of excrement as their signature of crime. The best elimination strategy is to prevent mice from getting into the walls in the first place, but if you've already heard the pit-a-pat of their little feet, you've got some exterminating to do.
The Damage Done
Mice come into homes looking for a nesting area, and a wall filled with fiberglass or cellulose insulation is ideal. While rearranging the insulation, which could create passages for cold air to enter your home, they chew electric wiring and sometimes even plastic water pipes -- simply because they are rodents and have to chew something. Eventually they get hungry, and that's when you begin to see them scurrying through the kitchen at night, contaminating your uncovered food and spreading disease. Once back in the nest, they reproduce quickly, and soon you have to deal with an entire colony.
Keeping Mice Out
Before you can effectively get rid of the mice that are already in your house, you need to prevent more from entering, or your efforts will be for naught. You may not find this job easy, because it involves painstakingly examining the foundation and underside of your house for mouse-sized holes -- which can be as small as a dime -- and blocking them. Block outright holes with metal plates-- mice can chew through wood -- and fill cracks and crevices with epoxy putty. Deploying a commercial rodent repellant may help keep mice away.
Once you've sealed the house against new intruders, it's safe to deal with the ones already inside. This may be a good time to get that cat you've always wanted, as cats naturally look at mice as prey, although you run the risk of the mice taking an interest in the cat's food bowl. If trapping is your best option, you may want to consider live traps -- small boxes that snap shut after a mouse enters. Your chances of success increase with the number of these traps you deploy and the type of bait you use -- peanut butter and brie cheese are best. Be sure to relocate the mice at least a mile from your home.
Invented in 1894, the swinging-jaw mousetrap continues to be the best way to catch mice; the more of these traps you set, the better. Alternatives include sticky pads -- which animal activists oppose because they cause more suffering to the animals than necessary -- and modern devices that zap mice with electricity, poison them with carbon dioxide gas or strangle them. It's best to stay away from poisons for two important reasons. One is that a dog or cat can that eats either the poison or a poisoned mouse will also be poisoned, and the other is that poisoned mice tend to die in the walls, creating odor and contamination.