Mice in the Walls: How to Tell and How to Keep Them Out
When temperatures drop, house mice look for warmth and food indoors. A mouse can squeeze through a gap about the width of a pencil, so even a well-kept house can have a few ways in.
Common signs
- Scratching or scurrying in walls and ceilings, mostly at night.
- Droppings about the size of a grain of rice, often along walls, in drawers, under sinks and in pantries.
- Gnaw marks on food packaging, baseboards, cords or cardboard.
- Nests made of shredded paper, fabric or insulation in hidden spots.
- A musky smell in closed spaces like cabinets.
How they get in
Common entry points include gaps around pipes and cables, spaces under garage and exterior doors, openings around dryer and AC lines, cracks in the foundation, and gaps where siding meets the foundation. Steel wool packed into small gaps and sealed with caulk is a common way to block small holes, since mice can chew through foam and plastic.
Cleaning up droppings safely
The CDC advises not to sweep or vacuum rodent droppings, because this can stir up dust that may carry viruses such as hantavirus (mainly spread by deer mice). Instead:
- Ventilate the area for at least 30 minutes.
- Wear rubber or plastic gloves.
- Spray droppings and nesting material with a disinfectant or a bleach solution (1 part bleach to 10 parts water) and let it soak for about 5 minutes.
- Wipe up with paper towels, bag and throw them away, then disinfect the area and wash your hands.
When to call a provider
A few mice caught early can sometimes be handled with traps and sealing. It is worth calling a provider if you keep finding fresh droppings, hear activity in several rooms, see mice during the day, or cannot find where they are getting in. Rats, which are larger and leave bigger droppings, are also a reason to get help sooner.