11 Signs of a Rodent Infestation (and How to Tell Which Rodent You Have)

Rodents are good at staying out of sight. Most people never see a mouse or rat until the problem is well established. What you can see are the signs they leave behind. Here are the eleven most common ones, and how to tell which rodent left them.

The 11 most common signs of rodents

1. Droppings. The most reliable sign. Look along walls, in cabinets and drawers, under sinks, in the garage and in the attic.
2. Gnaw marks. Rodents chew constantly. Look for fresh, light-colored marks on wood, plastic, food packaging and wiring.
3. Noises at night. Scratching, scurrying or thumping in walls, ceilings and attics after dark.
4. Nests. Balls of shredded paper, fabric, insulation or plant material in hidden spots.
5. Grease marks. Dark smudges along walls, beams and pipes where rodents rub as they travel the same route.
6. Odor. A musty, ammonia-like smell from urine, strongest in closed spaces.
7. Tracks and runways. Footprints and tail marks in dust, and worn paths along walls and fences.
8. Damaged food packaging. Chewed bags and boxes in the pantry or garage.
9. Chewed wiring. In attics, garages and under the hood of your car.
10. Pet behavior. Dogs and cats staring at, sniffing or pawing at walls and appliances.
11. Burrows and debris piles outside. Holes along foundations and woodpiles, or piles of sticks and cactus pieces under decks and sheds.

How to tell which rodent you have

Around Prescott, the rodents that get into homes are house mice, deer mice, pack rats and, less often, roof rats and Norway rats. The clues:

• Mice. Small droppings, about the size of a grain of rice. Light, quick scratching sounds. Small holes and gnaw marks.
• Roof rats. Dark, banana-shaped droppings about a quarter to half an inch long, according to the University of Arizona Cooperative Extension. Activity up high, in attics, ceilings and trees.
• Norway rats. Larger droppings with blunt ends. Activity down low, with burrows along foundations and under slabs.
• Pack rats. Large, messy nests of sticks, cactus and odd objects under decks, in sheds, garages and engine bays. Droppings often piled near the nest.

Our mouse control, rat control and pack rat removal pages go into more detail on each.

Old signs or an active infestation?

Fresh droppings are dark and moist-looking. Older droppings turn gray, dry and crumbly. New gnaw marks look light and clean, while old ones darken. Signs that point to an active, growing problem:

• Fresh droppings in several different rooms or areas
• Rodents seen during the day
• More than one nest
• A strong, spreading odor
• New damage appearing week after week

What to do next

1. Don’t sweep or vacuum droppings. Soak them with disinfectant first. Our droppings cleanup guide walks through it.
2. Note where you find signs. Activity clusters near entry points and nests, which helps whoever deals with the problem.
3. Look for the way in. Check garage doors, gaps around pipes and vents, and the foundation.
4. Get the problem identified. A free rodent inspection confirms which rodent you have, where it gets in and what it will take to fix.

If you are hearing noises in a specific place, our guides to rats in the attic and mice in the walls go into more detail.