Scratching sounds in an attic after dark point to one of two rodents: a house mouse or a Norway rat. Both species move indoors during colder months, when outdoor food sources drop and buildings offer warmth and shelter. A mouse infestation and a rat infestation require different trap sizes, different bait placement, and different exclusion work, so identifying the species correctly is the first step. This guide covers the physical signs of each rodent, how they get into attics and walls, the structural and health risks they create, and the point where do-it-yourself traps stop working. Homeowners across Westchester County, NY dealing with an active infestation can also find answers to 6 common questions at the end of this guide.
How to Tell If It’s Mice or Rats in Your Attic or Walls
House mice and Norway rats leave different physical evidence.
Mouse droppings measure about 1/8 to 1/4 inch long, taper to a point at both ends, and resemble a grain of rice. Norway rat droppings measure about 3/4 inch long, have at least one blunt end, and resemble a small olive pit. A mouse can squeeze through a gap roughly 1/4 inch wide, about the width of a pencil. A Norway rat needs a gap closer to 1/2 inch wide, about the width of a quarter.
Noise timing differs by species. Mice move quickly and produce light scratching or scurrying sounds, often shortly after dark. Norway rats are heavier and produce slower, more deliberate scratching or gnawing sounds, frequently overnight.
Four additional signs apply to both rodents:
- Gnaw marks on wood, wiring, or stored boxes
- Shredded insulation, paper, or fabric used as nesting material
- A strong ammonia-like odor from concentrated urine
- Grease marks along walls and beams where rodents repeatedly travel the same route
A single sign rarely confirms an active infestation. Fresh droppings alongside new gnaw marks indicate rodents are currently active rather than a past, resolved problem.
Why Mice and Rats Get Into Attics and Walls in the First Place
Mice and rats enter buildings to find warmth, food, and shelter from predators. Both species use existing gaps rather than creating new ones in most cases. Roof vents, soffit gaps, chimney flashing, foundation cracks, and openings around utility lines are the most common entry points.
Cold weather increases indoor rodent activity because outdoor food sources drop and rodents seek insulated, enclosed spaces. Attics and wall voids meet both needs: they stay enclosed, insulated, and undisturbed by daily household activity.
Older construction creates more entry points than newer construction. Original foundation seals, older utility penetrations, and gaps around window and door frames give rodents more access than sealing standards used in current construction.
Exclusion, the process of physically sealing every entry point a rodent can use, is the method that stops new rodents from entering after existing rodents are removed. Steel wool, hardware cloth, and metal flashing block gnawing. Caulk and expanding foam alone do not, since mice and rats chew through both materials.
The Real Damage (and Health Risk) They Leave Behind
Rodents in an attic or wall create three categories of damage: structural, electrical, and material.
Structural damage includes chewed roof decking, damaged soffits, and compressed or soiled insulation, which reduces the insulation’s effectiveness. Electrical damage includes gnawed wire insulation, which exposes bare wire and creates a fire risk inside a space where a spark is not immediately visible. Material damage includes shredded paper, fabric, and stored belongings used as nesting material.
Rodents also spread disease. The Centers for Disease Control and Prevention (CDC) links rodents to Salmonellosis, Leptospirosis, Rat-Bite Fever, and Hantavirus, spread through direct contact with droppings, urine, or saliva, and in some cases through a bite. The CDC recorded 890 hantavirus disease cases in the United States between 1993 and 2023, an average of roughly 30 cases per year nationwide.
The CDC recommends specific cleanup steps for rodent droppings and nesting material: ventilate the space for 30 minutes before cleaning, avoid vacuuming or sweeping since that spreads contaminated dust into the air, then spray the area with a bleach solution or EPA-registered disinfectant and let it sit for 5 minutes before wiping it up.
DIY Traps vs. Calling a Professional
Snap traps and glue boards catch individual rodents but do not address the entry points rodents used to get inside. A trapped rodent is quickly replaced by another one if the original entry point stays open, which is why DIY trapping alone rarely resolves an attic or wall infestation that has been active for more than a few weeks.
G-Man Exterminating’s rodent control process has four steps: evaluation and identification, securing points of access, applying treatment with specificity, and checking for and preventing new activity. Skipping the securing-points-of-access step is a common reason a DIY or partial treatment fails.
G-Man Exterminating holds New York pest control license #C3613019 and has served Westchester County, NY for more than 30 years, using pet- and family-friendly treatment methods. G-Man Exterminating provides a free quote before any work begins, and includes a free re-treatment between visits if rodents return before the next scheduled visit. Homeowners in Ossining, Yorktown, Mount Pleasant, Somers, and New Castle can find town-specific service details on G-Man’s location pages, or call (845) 226-6211 for a free quote.
Frequently Asked Questions About Mice and Rats in the Attic
The following 6 questions cover the most common concerns homeowners raise about mice and rats in the attic.
What smells do mice hate?
Mice avoid strong scents like peppermint oil and mothballs, but these scents only repel mice temporarily and do not address an existing entry point. A mouse that finds an open gap re-enters the space once the scent fades, regardless of which scent was used. Sealing entry points removes the reason a mouse would return.
How do you get rid of mice permanently?
Getting rid of mice permanently requires sealing every entry point a mouse can use, in addition to trapping the mice already inside. Trapping without exclusion work removes existing mice but leaves the entry point open for new mice. Exclusion combined with trapping addresses both the current infestation and future re-entry.
How long does it take to get rid of mice?
The time needed to get rid of mice depends on the size of the infestation and the number of entry points that need sealing. A property with a small number of entry points and light activity generally clears faster than a property with an established colony and several unsealed entry points.
How much does mice extermination cost?
Mice extermination costs vary by property size, the number of entry points found, and whether recurring service is needed. G-Man Exterminating provides a free quote before any work begins. New customers also receive $50 off enrollment in a recurring pest control plan, and first responders and active military members receive a 10% discount on their first treatment.
How do I know if I have mice or rats?
Mouse droppings measure about 1/8 to 1/4 inch long with pointed ends, while Norway rat droppings measure about 3/4 inch long with at least one blunt end. Mice produce light, quick scratching sounds, while Norway rats produce slower, heavier scratching or gnawing sounds. Gap size is a third indicator: a mouse fits through a 1/4-inch gap, while a Norway rat needs a gap closer to 1/2 inch.
Is hantavirus common in NY?
The CDC recorded 890 hantavirus disease cases nationwide between 1993 and 2023, an average of roughly 30 cases per year across the entire United States. The CDC reports case data by state, not county, and does not publish a Westchester County-specific or New York-specific case count in its public case summary. Hantavirus spreads primarily through inhaling dust contaminated with rodent urine or droppings, which is why the CDC recommends ventilating a space for 30 minutes before cleaning up rodent droppings rather than sweeping or vacuuming them.