As temperatures start to cool down, mice and other pests living outside start seeking warmer places to nest for the winter. In urban areas like New York City, their best choice might just be your nice, heated house or apartment building.
Knowing if and when a mouse has found its way into your home is the first step in getting rid of it. Left unchecked, house mice reproduce quickly and may potentially cause all sorts of damage to your walls, building, electrical wiring, and personal belongings.
If you suspect that you have a mouse in your cozy townhouse or apartment, here are 9 signs of mice to look out for. Finding one or more of these signs together might mean it’s time to give your exterminator a call.

9 Common Signs of Mice

1. Droppings

Mouse droppings are generally 1/8 to 1/4 of an inch in length, resembling dark grains of rice with tapered ends. Fresh droppings are usually dark brown, and over time they may lighten in color.
Droppings are often found where mice feed, such as in kitchen cabinets, pantries, and other areas where food is stored.
The amount of droppings that you find can be a good indicator of how serious the infestation is.

2. Scratching Noises

Scratching noises at night might be from a mouse scurrying around your home in search of food or shelter.
As they travel about, you might hear these sounds coming from behind walls, in the ceiling, or across the floor.

3. Odor

Mice emit a distinctive, musky smell that comes from the ammonia or urine. Mice use this odor to help establish themselves and mark their territory.
This odor may be more noticeable in enclosed areas like pantries, drawers, and cabinets.
Mouse odors that become stronger over time might indicate a growing number of mice in your home.
Unpleasant, rotting odors can also come from mice that have died.

4. Gnaw Marks and Scratches

In order to file down their teeth, mice will chew on inedible materials like wood, plastic, cables, and electrical wiring.
Check for grooves and markings along baseboards and around cracks or holes in your walls.
Gnaw marks and scratches are usually small and clean cut, consisting of two parallel grooves that are 1 to 2 mm apart.
If left alone, accumulated scratching and gnawing can lead to structural damage in your home.

5. Holes

Mouse holes might appear as damaged sections of walls or paneling, a small gap or hollowed crack in the foundation, or space created by crumbling mortar.
Check for gaps or cracks under and behind kitchen cabinets, inside closets, around doors and floor vents, and where the floor and wall meet.
Mice can fit through openings as small as a dime.

6. Runways

Mouse runways look like dirty or greasy smudges along floors and baseboards, created by their bodies and fur rubbing onto the surface.
Mice tend to follow the same path night after night, which creates these distinct tracks.
As you inspect your home, check walls and sidings with a flashlight to see any smudges or discoloration that might be tracks or rub marks from mice.

7. Nests

Mice like to use soft household materials like fabric, shredded paper, and insulation to build nests.
Nests are typically located in dark spaces. For example, inside cabinets and drawers or behind drywall and large appliances.
Mice tend to nest near food sources, so you’re more likely to find them in pantries or cabinets where food is stored.

8. Urine Pillars

Urine pillars are small mounds of grease, dust, dirt, and urine that shines under ultraviolet (black) light.
They can be found along active runways alongside mouse droppings and other signs.

9. Unusual Pet Behaviors

If your pet hears or smells a mouse in your home, they might show unusual interest in that spot.
They might appear extremely alert, have a vocal reaction like barking, or scratch at spaces under refrigerators, stoves, or low-clearance furniture pieces.