Mice in the garage: how to get rid of them and keep them out

A garage is everything a mouse wants: shelter from the weather, boxes to nest in, and usually something to eat. That’s why the first cold nights of fall are when most people find droppings by the bird seed. The fix has two halves: catch the mice that are already in, and close the way they got there.

Why mice pick the garage

Mice move indoors when it gets cold, and the garage is the easiest way in. A garage door seal doesn’t have to be damaged to let a mouse under, just worn. Once inside, they find what they need: grass seed, bird seed, pet food and the snacks in the car for nesting and food, and cardboard boxes, rags and insulation for bedding.

Signs you have them

• Droppings about the size of a grain of rice, along walls, on shelves and in drawers.
• Gnawed bags and boxes, especially seed, feed and pet food.
• Nests of shredded paper, fabric or insulation, tucked behind stored things or in a box nobody’s opened in a while.
• Greasy smudges along the bottoms of walls, where they run the same route every night.
• Scratching at night. Mice are most active after dark.

Find the way in

A mouse can squeeze through a gap about a quarter inch (6 mm) wide, roughly the width of a pencil. Check:

• the bottom seal of the garage door, and especially its corners
• gaps around pipes, wires, dryer vents and hose bibs where they pass through the wall
• the door between the garage and the house, which is how garage mice become house mice
• cracks in the foundation, and where the slab meets the wall

Pack small gaps with steel wool or copper mesh and seal over it with caulk. Use quarter-inch hardware cloth for vents and bigger holes, and replace a worn door seal. Mice chew through foam and plastic, but not through metal.

Trap the ones already inside

Seal and trap at the same time. If you only seal, the mice already inside are still inside.

• Go where they travel. Mice run along walls rather than across open floor, so set traps against a wall, near droppings or chewed packaging, or behind stored things.
• Plan on more than one. If you’ve seen one mouse, you probably have several. A single snap trap means a trip to the garage after every catch. A bucket trap keeps going until you empty it.
• Bait lightly. Peanut butter works best, in a small amount right where the mouse has to commit to reach it.
• Give it a few nights. Mice are wary of new things, so a quiet first night is normal. Leave the trap in the same spot before you move it.
• Check it every day. Keep any bucket with water in it where small children and pets can’t reach.

Take away the reasons to stay

• Move seed, feed and pet food into metal cans or heavy plastic bins with tight lids. Mice chew through bags and cardboard.
• Swap cardboard boxes for lidded plastic tubs, at least for anything soft that could become a nest.
• Clean out the car: wrappers and crumbs count. Storing a car for the winter? See keeping mice out of a stored car.
• Get things off the floor and away from the walls, so you can see the signs and the mice have fewer places to hide.

Clean up safely

Mouse droppings and urine can carry disease, so don’t sweep or vacuum them dry, because that puts dust in the air. The CDC recommends wearing gloves, spraying droppings and nesting material with a disinfectant or a bleach solution (1 part bleach to 10 parts water), letting it soak for five minutes, and then wiping it up with paper towels. Afterwards, wash your hands.

When to call a pro

If you’re seeing signs inside the house too, or new droppings keep turning up a couple of weeks after you’ve sealed and trapped, there’s an entry point you haven’t found. That’s worth a professional inspection.