How to get rid of mice in walls and ceilings

Step by step: how to get rid of mice in walls and ceilings

Safety first. Wear gloves when handling traps, droppings or nests, and wash your hands afterward. Do not sweep or vacuum mouse droppings, which can put viruses in the air; wet them with disinfectant first. If you use poison, it must be in a tamper-resistant bait station out of reach of children and pets, and a mouse that dies inside the wall will smell for weeks.

1. 1

   Listen and look to find where they travel

   Scratching at night inside a wall or ceiling usually follows the same route each time. Note where the sound starts and stops, then search the rooms above, below and on both sides with a flashlight for droppings, gnaw marks and greasy rub marks along baseboards.

2. 2

   Find the exit holes into living space

   Mice in walls come out to feed. Check under kitchen and bathroom sinks where pipes enter the wall, behind the stove, fridge and dishwasher, around the water heater and furnace, in closets, and at gaps around ceiling light fixtures and attic hatches. Fresh droppings and chewed edges mark the active holes.

3. 3

   Set traps where they come out

   Place snap traps along the wall next to each active hole, with the trigger end against the wall so a running mouse crosses it. Use a pea-sized dab of peanut butter or a little cotton as bait. Set traps about 10 feet apart or closer in busy areas, and in pairs a couple of inches apart where mice run.

4. 4

   Trap in the attic and basement too

   Mice in ceilings often travel from the attic or along the top plates of walls. Set traps along joists, beside insulation and next to droppings in the attic, and along sill plates and pipe runs in the basement or crawl space.

5. 5

   Check traps every morning

   Wearing gloves, put caught mice in a plastic bag, spray with disinfectant, seal it, and put it in the outdoor trash. Reset the trap. Keep trapping until a week passes with nothing caught and no new droppings or noise.

6. 6

   Seal the openings once trapping is done

   Pack coarse steel wool or copper mesh into every gap of 1/4 inch or more around pipes, wires and vents, then caulk over it. Cover larger holes with hardware cloth or metal flashing, and patch foundation cracks with mortar. Foam, plastic, rubber and wood alone get chewed through.

7. 7

   Seal from the outside as well

   Walk the outside of the house: utility entries, dryer and bath vents, gaps where siding meets the foundation, garage door seals and the soffits. Fit door sweeps, screen vents, and trim shrubs and vines away from the walls so mice cannot climb to the roofline.

8. 8

   Clean up droppings safely

   Open windows and air the room for 30 minutes first, as California’s Department of Public Health advises. Spray droppings and nest material with a fresh 10% bleach solution or a labeled disinfectant until soaked, wait at least 5 minutes, then wipe up with paper towels and bag them. Mop or wipe the area with disinfectant afterward.

Why you trap at the exits, not inside the wall

You trap mice where they leave the wall because that is where you can reach them and remove them. Mice stay close to home: UC IPM notes they seldom go more than 30 feet from their nest and food, can squeeze under gaps 1/4 inch tall, and climb any rough vertical surface, which is how they get between floors inside walls.

UC IPM also explains why trapping usually beats poison here: when you use bait, mice often die inside the structure, and the smell can be a real problem. With traps you see your success and remove the bodies.

What to seal mouse holes with

Seal mouse holes with metal or masonry, not foam or plastic. UC IPM calls exclusion the most successful and permanent form of house mouse control and lists plastic screening, rubber, vinyl, expanding foam and wood as ineffective because mice gnaw through them.

The EPA lists holes chewed through walls and floors as a sign of infestation, and notes that prevention can be as simple as plugging small holes with steel wool or patching holes in inside or outside walls.

Should you use poison for mice in walls?

Usually not. Poisoned mice tend to die in the wall or ceiling, and the smell of a dead mouse can last for weeks until it dries out. If you do use it, the EPA notes that consumer rodenticides are sold only as ready-to-use bait stations with block or paste bait, and that loose pellets are no longer allowed for consumer products. Place stations only where children, pets and wildlife cannot reach them, and follow the label.

If you already smell a dead mouse, find the warmest, strongest spot, and if it is reachable through a vent, access panel or attic, remove it wearing gloves and disinfect the area. If it is sealed in drywall, a contractor can cut a small access hole, or you can ventilate and wait for the smell to fade.

When to call a pest control professional

Call a licensed pest control professional if you keep catching mice after two weeks, if you hear larger animals (rats, squirrels or raccoons sound heavier and are active at different times), or if you cannot reach the attic or crawl space safely. Many pros offer exclusion work that seals the outside of the house.

Cleaning up after mice needs care: California’s Department of Public Health advises airing out the space for 30 minutes before you start, and warns that sweeping or vacuuming stirs up droppings that can spread hantavirus. For the full room by room approach, see how to get rid of mice in the house.

Mistakes to avoid

• Spraying expanding foam into holes, which mice chew straight through.
• Sealing the holes before trapping, which traps mice inside the walls.
• Using poison, so mice die in the wall and the room smells for weeks.
• Setting only two or three traps for a whole house.
• Sweeping or vacuuming up droppings instead of wetting them with disinfectant first.