Mice in the barn or shed: how to get rid of them and keep them out

A barn or shed gives a mouse everything at once: feed in bags, hay and straw to nest in, and corners nobody disturbs for weeks. Mice move in with the first cold nights and stay all winter. Getting rid of them means three things together: take away the food, close the way in, and trap the ones already there.

Why mice pick the barn

Mice follow food and shelter, and a barn has plenty of both. Grain, pellets, chicken feed and bird seed are the big draw, and a little spilled feed every day is enough to keep a family of mice going. Hay and straw bales, feed sacks, old blankets and stored equipment give them warm, dry places to nest. A shed is the same on a smaller scale: grass seed, fertilizer bags, cushions, and a lawn mower or tractor with a dry engine bay.

They breed fast. A pair of mice that moves in during the fall can become dozens by spring, which is why a few droppings in October are worth acting on.

Signs you have them

• Droppings about the size of a grain of rice, along walls, on shelves and around the feed bins.
• Chewed feed bags and a trail of spilled grain leading away from them.
• Nests of shredded paper, twine or insulation, tucked between bales or inside stored equipment.
• Chewed wiring on tractors, mowers and stored vehicles, or nesting material in an air filter box.
• Runs worn along the bottoms of walls, where they take the same route every night.

Cut off the food first

Trapping works much better when your bait isn’t competing with an open bag of feed.

• Keep grain, pellets and seed in metal cans with tight lids. Mice chew through plastic bins in time, and through paper sacks in a night.
• Sweep up spilled feed every day, especially under feeders and around the feed bins.
• Feed animals what they’ll finish, and don’t leave feed out overnight where you can avoid it.
• Stack hay and straw on pallets, a little away from the walls, so mice have fewer hidden runs and you can see the signs.

Find the way in

A mouse can squeeze through a gap about a quarter inch (6 mm) wide, roughly the width of a pencil. Barns are rarely tight, so focus on the gaps near food and nesting spots:

• the gap under doors, especially sliding doors, and where siding meets the foundation
• holes around pipes, wires and water lines where they come through a wall
• the walls of the feed room or tack room, which are worth sealing even if the rest of the barn isn’t
• on a shed, the floor edges, the door, and any gap where the floor sits on blocks

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

Trap the ones already inside

• Go where they travel. Mice run along walls rather than across open floor. Set traps against a wall, near droppings or chewed bags: the feed room and the wall behind the feed bins are usually the best spots.
• Plan on more than one. In a barn you almost never have just one mouse. Snap traps mean a trip out after every catch. A bucket trap catches one after another until you empty it. Set it against the wall with its ramp running along the wall, so a mouse following the edge walks straight onto 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.
• Mind the cold. In an unheated barn or shed, the water in a bucket trap can freeze, and a mouse that lands on ice can climb back out. In freezing weather, set it somewhere sheltered, like a heated feed or tack room. If nowhere stays above freezing, check it every day and break any ice.
• Keep it away from animals and kids. Any bucket with water in it is a drowning hazard for small children, kittens, chicks and other small animals. Put it where they can’t get to it.

Why poison is risky in a barn

Rodent poison doesn’t stay where you put it. Mice carry bait around and scatter it, and a poisoned mouse can be eaten by a barn cat, a dog, an owl or a hawk, which can poison them too. Around livestock, pets and the birds that hunt your mice for free, traps are the safer choice.

Barn cats and owls help keep numbers down, but they rarely clear a barn on their own, especially once mice are nesting inside the bales.

Clean up safely

Mouse droppings and urine can carry disease, and a closed-up barn or shed is exactly where the dust collects. Don’t sweep or vacuum droppings dry. The CDC recommends opening doors and windows to air the building out for at least 30 minutes first, then 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 wiping it up with paper towels. Afterwards, wash your hands.

When to call a pro

If you’re finding signs in the house as well, seeing rats rather than mice, or new droppings keep turning up a few weeks after you’ve cleaned up, sealed and trapped, it’s worth a professional inspection.