It usually starts after the house goes quiet. A faint scratching behind the bedroom wall, a quick scurry, then silence. If you suspect mice in walls, you are not imagining things: Kansas State Research and Extension lists sounds of gnawing, squeaking, or climbing in walls, ceilings, or between floors as signs of house mice, and NC State Extension describes "scratching and clawing noises within wall voids."
This guide covers how to confirm what you are hearing, what to do first without opening up the wall, what to avoid, and when to call a licensed pest control professional.
The Short Answer
Work from outside the wall: confirm the signs, find and seal the gaps they use to get in, set snap traps where they come out, and keep checking until activity stops. Avoid anything that leaves a mouse to die inside the wall, and call a professional if the problem is in places you cannot reach or keeps coming back.
Is It Really Mice in the Walls?
Several animals use wall voids. The Cornell Cooperative Extension guide "Beasts Begone!" describes their sounds and habits, and timing is the most useful clue:
- House mice are largely, but not only, active at night. Expect squeaking, scampering, and gnawing.
- Gray and red squirrels are active during the day, so chattering or scampering in daylight points to squirrels.
- Flying squirrels are nocturnal, with high-pitched twitters and "landing" noises at night.
- Bats are nocturnal and can make high-pitched clicking and scratching in walls and attics.
- Rats are mostly active at night too, according to UC IPM, and are much larger than mice.
The same Cornell guide notes that people sometimes mistake mechanical sounds, such as a smoke alarm with a low battery, for animals. Rule those out first.
What to Do First When You Hear Mice in Walls
Step 1: Look for supporting signs
Check along the base of the wall, under sinks, and behind appliances. NC State Extension says mouse droppings are found throughout the home, especially along walls, in corners, and under sinks, and that nests of chewed paper, insulation, and fabric are often hidden in wall cavities. A musky smell is another clue. Our guide to what mouse droppings look like helps you tell them apart from other animals.
Step 2: Find where they get in and out
The CDC lists places to check inside, including behind kitchen cabinets and appliances, around pipes under sinks and leading to water heaters and furnaces, around floor and dryer vents, around utility lines, and where the floor meets the wall. Outside, check the roofline, around windows and doors, between the foundation and the ground, and around holes for utility lines. The Cornell guide adds that deer mice and white-footed mice often get into wall voids through attached garages, so check the garage too. See how mice get into your house for a full walk-around.
Step 3: Seal the gaps
The CDC says mice can fit through a hole the width of a pencil, about 1/4 inch. It recommends filling small holes with steel wool and holding it in place with caulk or spray foam, and using hardware cloth, metal sheeting, or cement for larger openings. NC State Extension cautions that expanding foam alone is not recommended because mice may chew through it.
Step 4: Set snap traps where mice come out
Once gaps are sealed, the CDC recommends setting traps to catch mice still inside. Use snap traps sized for mice. Place them on the floor against the wall with the trigger end touching the wall, so they form a "T," in spots where you have seen signs and in enclosed areas such as behind the stove and in the back of cabinets. Chunky peanut butter works well. Keep traps out of reach of children and pets, and check them daily.
Step 5: Watch for a week
According to the CDC, if nothing is caught for a week and there are no new signs, the rodents are gone. If signs continue, look for an entry point you missed.
What Not to Do
- Do not use rodenticides indoors on your own. UC IPM notes that because house mice stay close to their nests, rodenticide use often results in mice dying inside the structure, which can leave odors in the wall. NC State Extension says rodenticides are best handled by pest management professionals.
- Skip glue traps and live traps. The CDC advises against them because they can scare rodents into urinating, which raises the chance of illness.
- Do not count on ultrasonic plug-ins. Kansas State Research and Extension says ultrasonic sound does not penetrate objects, and the mice are behind drywall.
- Do not expect scent to reach inside the wall. You cannot place or refresh a repellent inside a wall void, and NC State Extension says repellents are not a reliable form of mouse management.
When to Call a Professional
Call a licensed pest control professional if the sounds continue after a week or two of trapping and sealing, if you find signs in several rooms, if rodents are in places you cannot reach to clean, or if they have entered heating or cooling ducts. The CDC specifically recommends professional help for rodents in ventilation systems. A professional can also tell you if it is squirrels, bats, or rats instead.
If the noises are coming from overhead instead, read our guide to mice in the ceiling.
Cheat Sheet
- Night scratching, squeaking, and gnawing in walls often points to mice. Daytime noises point to squirrels.
- Confirm with droppings along walls, under sinks, and behind appliances.
- Find and seal gaps 1/4 inch or larger around pipes, wires, and vents.
- Use steel wool plus caulk for small holes, metal or cement for big ones.
- Set snap traps against the wall where mice come out. Check daily.
- No catches and no new signs for a week is the CDC's benchmark.
- Avoid indoor rodenticides, glue traps, and ultrasonic plug-ins.
Where BioGuard Fits
We sell BioGuard Natural Rodent Repellent, a pack of 12 scent balls infused with peppermint and cinnamon essential oils. It is not a fix for mice already living inside your walls, and we would not tell you otherwise. Where it can play a role is as an extra layer at the source, in an attached garage, a storage area, or near outside entry points after you have sealed them. Replace it every 4 to 6 weeks, keep it away from children, pets, and food, and expect results to vary.
Frequently Asked Questions
Will mice in the walls leave on their own?
Do not count on it. Kansas State Research and Extension stresses acting at the first signs so a few mice do not become an infestation.
Why do I only hear mice in the walls at night?
House mice are largely nocturnal. University of Arizona Extension notes two main feeding periods, at dusk and just before dawn, so those are often the noisiest times.
Should I cut a hole in the wall to get the mice out?
Usually not. Sealing entry points and trapping where mice come out is the approach the CDC describes. If you suspect a nest or a dead mouse inside a wall, a professional can decide whether opening it is needed.
How do I know if it is mice or rats in the walls?
Droppings are the easiest test. Mouse droppings are about 1/8 to 1/4 inch, while Norway rat droppings are 1/2 to 3/4 inch, according to Cornell Cooperative Extension.
Can mice climb inside walls?
Yes. UC IPM describes house mice as excellent climbers that can run up any rough vertical surface, Kansas State Research and Extension adds that they can travel horizontally along cables or ropes.
Sources
- CDC, How to Seal Up to Prevent Rodents
- CDC, How to Trap Up to Remove Rodents
- CDC, How to Clean Up After Rodents
- Kansas State Research and Extension, Controlling House Mice (MF1123)
- NC State Extension, Surveillance and Management of Common Structure-Invading Mice
- UC IPM, Pest Notes: House Mouse
- UC IPM, Pest Notes: Rats
- Cornell Cooperative Extension, NYS IPM, Beasts Begone! A Practitioner's Guide to IPM in Buildings
- University of Arizona Cooperative Extension, House Mice (Backyard Gardener)