If you’re hearing scratching, scurrying, or thumping inside your walls after dark, you almost certainly have a nocturnal animal that has found its way into a wall void or attic space. Mice, rats, squirrels, bats, and raccoons are the most common culprits, and each one sounds and behaves differently enough that you can usually narrow it down before calling anyone.
Identifying the Animal by Sound
The type of noise, its volume, and its timing tell you a lot. Mice produce light, rapid scratching, often accompanied by squeaking. Rats make heavier, slower movements and tend to stay quieter unless threatened. Both are nocturnal, so you’ll typically hear them after 10 p.m. If you hear consistent sounds from the same spot for multiple nights, a rodent has likely built a nest inside the wall rather than simply passing through.
Bats sound different from rodents. They produce high-pitched chirps and small rustling movements, usually concentrated in the upper walls or attic. You won’t hear heavy footsteps or gnawing from bats.
Raccoons are the loudest option. They create heavy thumping, scratching, and vocal sounds. Interestingly, raccoons are more active during the day than at night, so if your noises happen mostly in daylight hours with some nighttime activity, a raccoon is a strong possibility. Squirrels follow a similar daytime pattern, with lighter, faster running sounds than raccoons.
Scratching or chewing noises near the base of walls point toward mice, rats, chipmunks, or ground squirrels. Sounds higher up in the wall or along the ceiling lean toward bats, tree squirrels, or raccoons that entered from the roofline.
How They Get Inside
Animals exploit surprisingly small openings. Mice can squeeze through a hole the size of a dime. Rats need a gap roughly the width of a quarter. Squirrels need larger openings but will chew through rotted fascia or soffit to create one. Once inside, all three species build nests from shredded insulation, paper, and fabric.
The most vulnerable spots on a home’s exterior include loose or damaged soffit panels, rotted fascia boards along the roof edge, uncapped chimneys, damaged vent screens, and gaps where pipes or utility lines pass through the wall. Roof-to-wall transitions, where several materials meet in one place, are particularly weak points. Flashing that has lifted, rusted, or separated creates openings that rodents and raccoons will exploit. Overhanging tree branches, fences near roof edges, and trellises give animals a direct route onto your roof.
To find the entry point, look for loose soffits, chewed edges, open vents, stains or debris below an opening, and any spots where animals seem to travel the same path repeatedly. Watching your roofline near dusk or dawn can reveal animals entering or exiting. Taking clear photos from the ground is helpful if you end up calling a wildlife professional.
Why You Shouldn’t Ignore It
Wall-dwelling animals create real hazards beyond the noise. Rodents gnaw constantly to wear down their ever-growing teeth, and electrical wiring is a common target. Rodents are estimated to cause up to 20 percent of undetermined house fires in the United States each year by chewing through wire insulation.
Health risks depend on the species. Rodent droppings and urine can carry serious infections, including hantavirus and leptospirosis. Bat guano harbors fungal spores that cause histoplasmosis, a lung infection with flu-like symptoms that can become severe in people with weakened immune systems. Raccoon feces carry a roundworm parasite with its own set of dangers. The longer animals occupy a wall void, the more waste accumulates in insulation and framing that you can’t easily see or reach.
One critical safety note: when cleaning up animal waste, never vacuum or power wash it. These methods send particles airborne and directly into your lungs. Wet the material down first, wear a respirator, and bag waste in sealed plastic.
Getting Animals Out Safely
The general approach is called exclusion: you let the animal leave through its existing entry point, then seal the opening so it can’t return. This works well for rodents and bats but requires patience and correct timing.
For bats specifically, there are legal restrictions in most states. Bat maternity season runs roughly from May through August, and during this window you should not seal openings. Pups are flightless until around mid-July, so blocking exits during these months traps young bats inside your walls, where they die and create a worse problem. The best time to exclude bats is in early fall, after pups can fly but before winter hibernation.
For mice and rats, snap traps placed along known travel paths (near the base of walls, in the attic, or near entry points) are the most effective immediate step. Poison bait is riskier inside walls because a rodent that dies in an inaccessible void will decompose and smell for weeks. Once you’ve confirmed activity has stopped, seal the entry points.
Raccoons and squirrels in wall voids or attics are best handled by a licensed wildlife control operator. These animals are strong enough to tear through weak repairs, and raccoons in particular can be aggressive when cornered, especially mothers with young.
Sealing Entry Points for Good
The material you use matters. Galvanized hardware cloth in quarter-inch mesh is the standard for sealing openings against mice and bats. Half-inch mesh is stronger but won’t stop smaller animals. For larger openings or areas where raccoons are the concern, galvanized sheet metal attached with screws is more durable and resistant to clawing. Stainless steel mesh is the longest-lasting option and won’t rust. Aluminum flashing is easy to work with but only appropriate for birds and bats, since raccoons and rodents can chew or claw through it.
For small cracks and gaps around pipes or utility lines, copper mesh stuffed into the opening and sealed with caulk works well. Rodents dislike chewing copper. Expanding foam alone is not enough; mice chew through it easily.
If animals are digging under a foundation or slab to access wall voids, a buried barrier (sometimes called a rat wall) should extend one foot deep with a six-inch horizontal shelf at the bottom to prevent animals from tunneling beneath it.
After sealing, trim any tree branches that overhang or touch your roof, secure vent covers with hardware cloth, and cap your chimney. These steps eliminate the access routes that brought the animal inside in the first place.