Mouse droppings are small, dark and pointed at the ends, about an eighth to a quarter inch long, roughly the size of a grain of rice. You find them scattered rather than piled, in drawers, along baseboards, under sinks and in pantry corners. Rat droppings are several times larger.
In San Diego County, the mouse that leaves them is usually a house mouse. In homes near canyons, open space and the backcountry, it may be a deer mouse, which is the main carrier of hantavirus in California. The droppings look much alike, so where you live and where you find them matter for how you clean.
What mouse droppings look like
- Size: about an eighth to a quarter inch
- Shape: thin, with one or both ends pointed
- Color: dark brown to black when fresh, grayer when old
- Pattern: scattered along walls and in corners, often in large numbers
The CDC says rodent droppings are pointed at one end and often contain hair, and that they are common in cabinets and drawers. A mouse leaves many small droppings as it moves, so a few mice can leave a lot of evidence in a short time.
Mouse or rat?
Size is the quickest check. Rat droppings are roughly half an inch or longer and thicker. If you find both sizes, you may have both rodents, or young rats among adults. Location helps too. Mouse droppings show up low and close to food: kitchen drawers, the back of the pantry, under the stove and in the garage near pet food. Roof rat droppings show up high: attics, rafters and the tops of walls. See rat droppings identification.
House mice and deer mice
House mice are gray-brown all over and live close to people. The county says house mice do not carry hantavirus.
Deer mice are brown on top with a white belly and a tail that is dark above and white below. The county says deer mice are the main carriers of Sin Nombre virus and are found mostly in rural areas, the desert and the mountains. Around San Diego, that means homes on canyon rims and next to open space, and properties in East County, North County inland and the backcountry. Deer mice nest in sheds, garages, cabins, RVs and patio storage more than in kitchens.
You cannot tell house mouse droppings from deer mouse droppings by eye with any confidence. If you live near open space or find droppings in a closed shed or cabin, clean as if deer mice were there.
Where the mice are coming from
Mice need much smaller openings than rats. The county's hantavirus brochure says to seal holes dime-sized or larger. The droppings map points to the route:
- Droppings behind the stove or dishwasher: gaps around gas and water lines
- Droppings under the kitchen sink: gaps around the drain and supply pipes
- Droppings in the garage along the door: a worn bottom seal or side gap
- Droppings in a closet on an outside wall: gaps at the base of the stucco or around cable lines
How to clean mouse droppings
Do not sweep or vacuum. Follow the CDC wet method:
- Open doors and windows for 30 minutes
- Wear rubber or plastic gloves
- Spray droppings with a solution of 1 part bleach to 9 parts water and let it soak 5 minutes
- Wipe up with paper towels and put them in a covered trash can
- Mop or sponge the area with disinfectant
- Wash your hands after removing gloves
In sheds, cabins and garages near open space, use the county's stricter steps: air out at least 2 hours, add a mask and eye protection, and soak 15 minutes. Throw out food that has droppings on it or on its packaging. Wash dishes and utensils from contaminated drawers in hot soapy water. See droppings cleanup.
After cleaning
Check the same spots in two or three days. New droppings mean mice are still active, and the CDC uses that as its sign of an active infestation. Set snap traps along the walls where you found the most droppings, seal the gaps you can reach, and call for help if the droppings keep coming back. See mouse control.
Droppings in cars, RVs and storage
Mouse droppings in a car's glove box, cabin air filter or engine bay mean mice are nesting in or near the vehicle. RVs, boats and trailers that sit in driveways or storage lots are common nest sites, especially near open space. Before you clean one out, open it up to air for a while and follow the wet cleaning steps above. Check the cabin air filter and the engine bay for nesting material. See rats in the garage and car engine.