Rat droppings are dark brown to black, roughly half an inch to three quarters of an inch long, and shaped like a fat grain of rice or a small olive pit. They show up in clusters along the paths rats travel, such as attic joists, the top of walls, behind stored boxes and along garage shelves. Mouse droppings are much smaller, about the size of a grain of rice.
In San Diego, most rat droppings come from roof rats, which the county calls the most common rat here. Finding them in the attic or high on garage shelves fits that pattern. Here is how to read them and how to clean them up.
Size and shape
Use a coin or a ruler for scale and take a photo before you clean.
- Roof rat droppings: about half an inch long, slender, with pointed or slightly curved ends
- Norway rat droppings: larger and thicker, up to about three quarters of an inch, with blunter ends
- Mouse droppings: about an eighth to a quarter inch, thin and pointed, like dark grains of rice
The CDC notes that rodent droppings are pointed at one end and often contain hair. A spread of sizes in one spot can mean adults and young rats, or rats and mice together.
Fresh or old
Fresh droppings are dark and shiny, soft and a little moist. Within a few days they dry out, turn dull and go hard. Old droppings crumble when pressed with a stick and often turn gray.
The CDC gives a simple test: clean the area, then check again in a few days. New droppings mean rodents are still active. Old droppings alone tell you rodents were there at some point, not that they are there now. That test is useful when you buy a house or open a long-closed attic.
Where rat droppings show up in San Diego homes
Roof rats live high, so their droppings do too. Look for:
- Attic joists and the tops of HVAC ducts
- Along the top plates of walls in the attic
- Garage shelves, rafters and the top of the water heater closet
- Inside lower kitchen cabinets near pipes
- Patio covers, pool equipment enclosures and storage sheds
- Under fruit trees, along with gnawed fruit
Droppings in piles in one corner can mark a latrine spot near a nest. Scattered droppings along a straight line mark a runway, which is the best place for traps. See rats in the attic.
Other signs that go with droppings
The county lists rub marks from greasy fur, gnaw marks on wood, cardboard, plastic or wires, stripped tree bark, damaged food and a sweet, musty smell from rat urine. In attics, look for tunnels and flattened paths through the insulation. Outside, look for piles of empty snail shells under garden plants, which the county also lists as a rat sign.
How to clean rat droppings safely
Do not sweep or vacuum droppings. Both put particles in the air. The CDC steps are:
- Open doors and windows for 30 minutes before you start
- Put on rubber or plastic gloves
- Mix 1.5 cups of household bleach in 1 gallon of water, or 1 part bleach to 9 parts water
- Spray the droppings and let them soak for 5 minutes, or follow the disinfectant label
- Wipe up with paper towels and throw them in a covered trash can
- Mop or sponge the area with disinfectant
- Wash your hands after removing gloves
For closed spaces like sheds or cabins where wild mice may have lived, the county's 2026 hantavirus brochure suggests airing out for at least 2 hours, wearing a mask and eye protection, and soaking for 15 minutes. See droppings cleanup.
What droppings tell a provider
If you call for help, describe the size of the droppings, where you found them and how fresh they looked. Photos help. Droppings in the attic point to roof rats coming in at the roofline. Droppings low in the garage or kitchen point to mice or to rats using a ground-level gap. That tells the technician where to start. See rat control.
Health questions
Rat droppings and urine can carry germs. The county lists food poisoning from food contaminated with urine or droppings, and leptospirosis from contact with infected urine or contaminated water or soil, among diseases rats spread. Throw out any food with droppings on it or its packaging. See rodent diseases in San Diego.