The fastest way to identify an animal in your wall is by combining two clues: the sounds it makes and the time of day you hear them. Scratching at night usually points to mice, rats, or raccoons. Scurrying during the day almost always means squirrels. From there, droppings, entry hole size, and smell can confirm exactly what you’re dealing with.
What Time of Day You Hear the Noise
This single detail narrows the list dramatically. Most animals that end up in walls are nocturnal, meaning you’ll hear them in the evening, through the night, or right around dawn. Mice, rats, raccoons, bats, and opossums all fall into this category. If your wall comes alive after dark, you’re dealing with one of these.
Squirrels are the major exception. They’re active during daylight hours, so if you hear running, scratching, or scurrying while the sun is up, squirrels are the most likely culprit. They typically get loud in the early morning and late afternoon as they leave and return to their nesting spot.
What the Sounds Tell You
Each species makes a distinct set of noises, and learning the differences saves a lot of guesswork.
- Mice: Light scratching and scurrying, sometimes faint squeaking. You may also hear a subtle gnawing sound, especially if they’re chewing on wires. The sounds are quiet enough that you might only notice them when the house is still.
- Rats: Similar to mice but louder and heavier. The scratching is more pronounced, and you’ll hear more deliberate movement rather than the quick, skittery sounds mice make.
- Squirrels: Fast, persistent scurrying and scratching during the day. They sound like they’re running back and forth rather than staying in one spot. The noise level falls between mice and raccoons.
- Raccoons: Heavy thumping. An adult raccoon averages around 40 pounds, so there’s nothing subtle about it. You may also hear mewing or crying sounds, especially if a mother has babies with her. Raccoons make the most “ruckus” of any common wall or attic invader.
- Bats: Squeaking, light flapping, and occasional thumping. These sounds are faint and you’ll typically only hear them if you’re standing close to the wall or ceiling where they’re roosting.
Check for Droppings
You may not be able to see inside the wall, but droppings often show up near entry points, in the attic, along baseboards, or in the garage. The size and shape differences between species are surprisingly distinct.
Mouse droppings are tiny, about 1/8 to 1/4 inch long, shaped like dark grains of rice with tapered ends. Rat droppings are noticeably bigger. Roof rat droppings measure 1/2 to 3/4 inch with pointed, spindle-like ends. Norway rat droppings are the largest of the rodent group, 3/4 to a full inch long with blunt ends and a sausage-like shape.
Squirrel droppings are small, cylindrical pellets with rounded ends, generally dark brown or black. They’re easy to confuse with rat droppings at first glance, but squirrel pellets tend to be rounder and less tapered. Raccoon droppings look like what you’d expect from a medium-sized dog: 2 to 3 inches long, tubular with blunt ends. You’ll often see undigested seeds, berries, or shell fragments mixed in. Bat droppings accumulate in clusters or mounds below roosting spots. Fresh ones look moist and shiny, but they dry out and become crumbly quickly.
Look at the Entry Point
Finding where the animal got in tells you a lot about what it is. Walk the exterior of your home and look for gaps, holes, or damage around the roofline, foundation, vents, and utility lines.
Mice need shockingly little space. A gap the width of a pencil, roughly 1/4 inch, is enough. That’s about the size of a dime. Rats need slightly more, around 1/2 inch, or about the size of a quarter. Bats can squeeze through gaps as narrow as 1/4 to 3/8 of an inch, typically around soffits, rooflines, vents, and fascia boards. If you find a gap that small in your upper story or roofline and you’re hearing faint squeaking at night, bats are a strong possibility.
Squirrels and raccoons need bigger openings and often create them. Look for chewed-out holes in soffits, torn vent screens, or damaged fascia. A raccoon can pry open surprisingly sturdy materials with its hands. If the entry point looks like something was ripped or torn rather than gnawed, you’re likely dealing with a raccoon.
Smell as a Clue
A musky, ammonia-like odor near a wall often signals an active nest, particularly with mice or rats. Their urine accumulates over time and produces a distinctive stale smell that gets stronger the longer the colony stays.
A different kind of smell, a strong and unmistakably rotten odor, usually means an animal has died inside the wall. A dead mouse may produce a noticeable smell for about 10 days, sometimes lingering for a few weeks. Larger animals like rats or squirrels take longer to decompose and the odor lasts longer. A dead raccoon can produce a smell that persists for several weeks. If the smell appeared suddenly and is getting worse day by day, decomposition is the likely cause.
Using Technology to Confirm
If you want visual confirmation without cutting into drywall, two tools can help. A thermal imaging camera detects heat signatures through walls. Entry-level models that attach to your phone can reveal warm spots from a nest or a cluster of animals. Nocturnal animals can also be tracked with thermal imaging in complete darkness, so scanning your exterior walls at night can show you where they’re entering and exiting.
A borescope, a small flexible camera on a cable, lets you look inside wall cavities through a tiny drilled hole or an existing gap. These are available for under $50 and plug into a smartphone. Drilling a small hole near where you hear the sounds and feeding the camera in can give you a definitive answer.
Health Risks Worth Knowing About
Animals in walls aren’t just a nuisance. Rats and mice spread over 35 diseases worldwide. One of the most serious in the United States is hantavirus, primarily carried by deer mice. You can be exposed simply by breathing in dust contaminated with rodent droppings or urine, which makes cleaning up after an infestation something to approach carefully. Wet down droppings with a disinfectant solution before sweeping or vacuuming to avoid stirring up particles into the air.
Bat droppings can harbor fungal spores that cause a lung infection called histoplasmosis when inhaled. Raccoons carry their own set of risks, including a roundworm parasite found in their feces. If you discover a large accumulation of droppings from any species, wearing a respirator during cleanup is a reasonable precaution.
Legal Restrictions on Removal
Before you take action, know that some animals are legally protected. Bats are the most common example. In Florida, it’s illegal to block bats from returning to their roost during maternity season, which runs from April 16 through August 14. Outside of maternity season, you can use one-way exclusion devices that let bats leave but prevent reentry, but the devices must stay in place for a minimum of four nights and overnight temperatures must be forecast at 50°F or above. Many other states have similar seasonal restrictions. Killing or harming bats is illegal in several states year-round.
Raccoons, squirrels, and other wildlife may also have local protections depending on your state. Checking with your state’s fish and wildlife agency before attempting removal keeps you on the right side of the law.
Sealing Up After Removal
Getting the animal out is only half the job. If you don’t seal the entry points, the same species (or a new one) will move right back in.
For small gaps where rodents or bats entered, stuff the opening with copper mesh or steel wool and seal over it with caulk or urethane expanding foam. Rodents can chew through foam alone, but they can’t chew through metal mesh. For vents in the attic, roof, or crawl space, install 1/4-inch wire mesh (hardware cloth) over the opening to block birds, bats, squirrels, and rodents while still allowing airflow.
Check the base of all exterior doors for gaps. If you can see light under the door while lying on the floor, add a door sweep or threshold. Garage doors should have a rubber bottom seal (vinyl cracks in cold weather). Don’t forget utility openings where pipes, wires, outdoor faucets, gas meters, and dryer vents pass through the foundation or siding. These overlooked spots are some of the most common entry points. A chimney cap is one of the simplest investments you can make to keep raccoons, squirrels, and birds from coming in from above.