Quick answer: The signs of a rodent infestation are droppings along walls and in cabinet corners, gnawed packaging, greasy rub marks on baseboards, shredded nesting material, a musky urine smell and scratching in the walls after dark. Dropping size tells you mouse or rat, and soft, shiny droppings mean the activity is current.
Key takeaways
- Mouse droppings are 1/8 to 1/4 inch long and Norway rat droppings 3/4 to 1 inch, according to Cornell University’s IPM program, so one dropping tells you which rodent you have.
- A female house mouse can have 5 to 10 litters of 5 or 6 pups a year, according to the University of California IPM program, so one mouse in October is a family by Thanksgiving.
- Never sweep or vacuum dry droppings; the CDC warns that this can put virus particles into the air, so wet them with disinfectant first.
Where do the signs of a rodent infestation show up in the kitchen?
Start low and in the corners. Rodents travel with one side against a wall, so droppings collect where the floor meets the cabinet base, in the back corners of lower cabinets and under the sink. Mouse droppings look like dark grains of rice with pointed ends; rat droppings are larger and blunter.
On pantry shelves, look for gnawed corners on cereal boxes and pet food sacks. Behind the stove and refrigerator, check for dark, greasy smudges around pipe openings; those rub marks build up where a rodent squeezes through the same gap every night. A sharp, musky smell in a closed cabinet is urine.
What does rodent activity in the attic look like?
Go up with a bright flashlight and a mask, and look at the insulation first. Rodents press tunnels into blown-in insulation, pull batts apart for nesting and leave droppings near warm spots such as the furnace flue and recessed light cans.
A nest is a loose ball of shredded insulation, paper or fabric, often tucked against a joist or inside a stored box. Urine shows as yellow-brown staining, and a heavy infestation smells at the hatch.
Look closely at the wiring. Rodents gnaw because their front teeth never stop growing, and the University of California IPM program notes that house mice damage structures by gnawing on electrical wires and gas lines. Chewed wiring is a fire hazard, so have an electrician look.
What is the scratching in the walls at night?
Usually a rodent moving between the attic or crawl space and the food. Mice make a light, quick scratching; rats are heavier, with thumps, steady gnawing and a slower scamper. Squeaking from one spot often means a nest with young.
Rats and mice are most active after dark, so most people hear them within an hour of lights out and again before dawn. Roof rats favor attics and ceiling voids, so a runner overhead is usually a rat. Pets that bark or stare at a blank wall are tracking something you cannot hear.
Garage, crawl space and yard: signs outside the living space
Many infestations start in the garage. Look for gnawed cardboard, nests in stored fabric, droppings behind the freezer and chewed door sweeps on the overhead door. Pop the hood on any car that sits for days; our guide to mice in car engine bays and RVs covers what you may find.
In the crawl space, look for droppings on the vapor barrier, insulation pulled down between the joists, tunnels along the stem wall and torn vent screens. Our article on rodents in the crawl space explains why Oregon homes are so prone to this.
Outside, walk the foundation. Norway rats burrow along foundations, under sheds and woodpiles, leaving smooth-edged openings a couple of inches across. Worn paths under decks, half-eaten fruit or filberts under trees and greasy marks on fence tops point to roof rats, which travel above ground.
What do the signs tell you?
Size first. Cornell University’s IPM program puts mouse droppings at 1/8 to 1/4 inch, roof rat droppings at about 1/2 inch and Norway rat droppings at 3/4 to 1 inch. Gnaw marks follow the same rule: paired grooves 1 to 2 millimeters wide mean a mouse, 3.5 to 4 millimeters a rat. Our guide to rat droppings vs mouse droppings goes deeper.
Age and numbers next. Fresh droppings are dark, shiny and soft; old ones are gray and crumbly, and both together means weeks of activity. UC IPM notes that house mice seldom venture more than 30 feet from the nest, so droppings at opposite ends of the house mean more than one nest. Two dropping sizes in one spot mean adults and juveniles, which means breeding.
Sizes below come from Cornell University’s IPM program and UC IPM; the cleanup step follows CDC guidance.
| Sign | What it looks like | Mouse or rat | Fresh or old | What to do next |
|---|---|---|---|---|
| Droppings | Dark pellets along walls and in cabinet corners | Mouse: 1/8 to 1/4 inch. Rat: 1/2 to 1 inch | Fresh: shiny and soft. Old: gray and crumbly | Wet with disinfectant, then recheck in a week |
| Gnaw marks | Chewed packaging, wood, wiring, door sweeps | Mouse: grooves 1 to 2 mm wide. Rat: 3.5 to 4 mm | Fresh: pale and splintery. Old: dark and smooth | Store food in hard containers; check wiring |
| Rub marks | Greasy smudges along baseboards, beams and pipes | Mostly rats | Fresh: smears. Old: flakes | Trace it to the entry point and trap along it |
| Burrows and runways | Smooth-edged holes at the foundation, worn paths under decks | Burrows: Norway rats. Fences and wires: roof rats | Fresh soil: active. Webs or leaves: old | Remove cover and food, then trap |
Four things not to do
- Do not sweep or vacuum dry droppings. The CDC says this can put virus particles into the air; open windows for 30 minutes and wet everything with disinfectant first. Our guide to cleaning up mouse droppings covers the routine.
- Do not seal every opening while rodents are inside and call it done. Trap at the same time, so nothing gets shut into a wall to die.
- Do not count on repellents or ultrasonic plug-ins; UC IPM finds little evidence that sound or vibration devices drive established rodents out of a building.
- Do not place poison bait where children or pets can reach it; use tamper-resistant stations exactly as the label says.
Rodent signs in Salem and the Willamette Valley
The valley’s calendar sets the timing. After September’s dry spell, the first cold rains of October push mice and rats indoors, and in our experience rodent calls across Salem, Keizer and Albany climb from then until the holidays. Harvest around Silverton and Stayton clears fields and orchards at the same time.
Roof rats climb and eat fruit and tree nuts, so older Salem, Woodburn and McMinnville neighborhoods with big trees, ivy and fruit trees see them in attics. Norway rats stay low, burrowing near creeks, the Willamette and older sewer lines, then entering through crawl spaces. Our roof rats vs Norway rats guide shows where each hides.
On rural Polk and Marion County properties, from Dallas and Monmouth out to the foothills, the mouse in the shop or barn is often a deer mouse, and the CDC notes that the most common hantavirus in the United States is spread by the deer mouse. Many valley homes also sit over damp crawl spaces in clay soil; our checklist of mouse entry points covers seven spots to check before the rain.
When should you call a professional?
Call when you find rat sign anywhere, mouse sign in more than one room, noises lasting more than a few nights, or chewed wiring. One mouse in the garage is a job for a few snap traps and a tube of sealant; a rat in the attic in October is not.
A professional rodent program typically involves:
- A whole-structure inspection, roofline to crawl space, to identify the species and find the entry points.
- Snap traps along the runways the inspection found, checked until the catches stop.
- Exclusion: sealing entry points with steel wool backed by sealant, hardware cloth or metal flashing.
- Any exterior bait in tamper-resistant stations per the label, plus cleanup guidance and a follow-up check.
AAA Pest Exterminators has been family-owned and operated in Salem since 1997, with no long-term contracts. Our rodent control service handles mice and rats across the valley.
Frequently asked questions
How do I know if I have mice or rats?
Measure the droppings. Mouse droppings are 1/8 to 1/4 inch long; rat droppings are 1/2 inch or longer and thicker. Rat gnaw marks are about twice as wide as a mouse’s. Noise overhead points to roof rats, heavy sounds low in the walls to Norway rats, and light scratching to mice.
How many mice are there if I saw one?
More than one, usually. Mice are nocturnal and secretive, so a mouse out in daylight often means a crowded nest. They rarely travel more than about 30 feet from the nest, so droppings at both ends of the house mean more than one nest. Set several traps along the walls and see how fast they fill.
Do rodents leave in summer?
Not on their own. Mice that nested inside stay inside, and roof rats that found your attic keep using it even when summer fruit keeps them outside more. Warm weather just means quieter walls and less fresh sign. The first cold rains of October bring the whole population back, plus new litters.
How fast do mice breed?
Fast enough that waiting is the expensive choice. A female house mouse can have 5 to 10 litters a year of about 5 or 6 pups each, and the young can breed at 5 to 6 weeks old, according to the University of California IPM program. Two mice in October can be dozens by January, so fresh droppings deserve traps the same day.
Pests in the nest? Don’t stress. Call the best.
Family-owned and operated in Salem since 1997. No long-term contracts. Serving Salem, Keizer, Albany, Dallas, Woodburn and McMinnville.
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