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How to identify it
- Adults weigh about 1/2 ounce and are 5 to 7 inches long including a 3- to 4-inch tail; light brownish to gray with relatively large ears and small black eyes.[1]
- Measurements differ a little: the Internet Center for Wildlife Damage Management (ICWDM) gives a body of 3 to 4 inches, a tail of 2 to 4 inches and a weight of 0.4 to 0.9 ounces.[5]
- The tail is almost hairless, and the belly is not bright white.[1][2][5]
- Signs include droppings, gnaw marks, tracks, nests of finely shredded paper or fiber, and a musky odor in large infestations.[1][5]
- Droppings average about 1/4 inch long, according to ICWDM. Cockroach droppings usually run 1/8 to 1/4 inch, with ridges along their length and squared-off ends. CDC notes rodent droppings are pointed at one end and often contain hair.[5][7]
- ICWDM calls a musky odor a positive sign of mice, and one that sets them apart from rats.[5]
Look-alikes
| Look-alike | How to tell them apart |
|---|---|
| Deer mouse | Larger eyes, a bright white belly and feet sharply separated from the brown back, and a furred, two-toned tail.[1][2] |
| Young rat | A young rat has a large head and feet for its body. Gnaw-mark widths differ by source: UC IPM gives about 1/6 inch for rats versus a mouse's scratchy 1/12 inch, while ICWDM gives 1/16 inch for rats and 1/32 inch for mice. Either way, mouse marks are the smaller.[3][5] |
Where it lives
Found worldwide; native to Central Asia and brought to North America by ships. Outdoor mice often move into homes in autumn as nights turn cold.[1]
Biology and life cycle
A female can have 5 to 10 litters of about 5 or 6 pups a year; young mature in 5 to 6 weeks.[1]
Mice eat about 200 small meals a night and seldom travel more than 30 feet from their nest; they don't need to drink water to survive.[1][6]
They squeeze under 1/4-inch gaps and through 3/8-inch openings, and climb rough walls. Jump heights differ: UC IPM says up to 12 inches, ICWDM up to 10 inches from a flat surface.[1][6]
Nests of fine, shredded material turn up in garages, closets, attics, basements and outbuildings.[5]
Damage and signs
Health risk
CDC says the house mouse spreads lymphocytic choriomeningitis (LCM) virus and lists rodents, including mice, among the animals that spread leptospirosis. Mouse droppings, urine and saliva can make people sick when the contaminated air is breathed in or contaminated food is eaten.[13][11][7]
Control
Keep them out
Exclusion is the most successful and permanent rodent control: seal every gap larger than 1/4 inch with metal or concrete, including around pipes, vents and utility lines, and make doors, windows and screens fit tightly. Foam, plastic, rubber and wood are gnawed through.[1][3]
CDC says a mouse fits through a hole the width of a pencil, 1/4 inch; ICWDM also says to seal openings larger than 1/4 inch, using hardware cloth. For small holes CDC suggests steel wool held in place with caulk or spray foam, while UC IPM lists expanding foam among materials mice gnaw through.[8][6][1]
Sanitation
Remove food, water and shelter: store food in rodent-proof containers and declutter; sanitation alone seldom eliminates mice but poor sanitation lets them thrive.[1][8]
Traps and physical control
Trapping is the preferred method in homes with only a few mice: set snap traps along walls with the trigger toward the wall, no more than about 10 feet apart, baited with a small amount of food or nesting material such as cotton.[1]
Trap spacing differs: UC IPM says no more than about 10 feet apart, ICWDM no more than 6 feet apart where mice are active. Peanut butter works as bait for both ICWDM and CDC, and CDC says to set the baited end against the wall so the trap forms a T with it.[1][6][9]
ICWDM says glue boards catch fewer mice than other traps, and CDC advises against glue and live traps because frightened rodents urinate, raising the risk of disease. ICWDM does not recommend ultrasonic devices: in tests they kept rodents away for only a few days.[6][9]
Pesticides
Rodenticide baits sold to the public are limited to wax block, gel or paste baits packaged in or with ready-to-use, disposable bait stations; poisoning inside buildings can leave dead rodents in walls, which is one reason trapping is preferred indoors.[3][1]
CDC puts poison and bait stations last, for mouse infestations that persist after trapping, and recommends EPA-registered products.[9]
When to call a professional
There is no simple fix: an infestation almost always needs population reduction combined with sanitation and exclusion.[1]
Health risks in more detail
LCM: most healthy people infected have no symptoms or mild ones, CDC says, but it is serious for pregnant women, since it can cause miscarriage or birth defects, and for people with weakened immune systems. People catch it from fresh urine, droppings, saliva or nesting material of infected mice.[13]
Hantavirus: in the United States, CDC says the hantavirus that most often causes hantavirus pulmonary syndrome is spread by the deer mouse, not the house mouse, which is one reason to tell the two apart.[12]
Allergy: in a study of 499 inner-city children with asthma, 18% tested positive for mouse allergy, and children from homes with more mouse allergen in the kitchen were more often sensitized. The same study did not find a statistically significant link between mouse allergen exposure or sensitization and measures of asthma illness.[14]
Cleaning up after mice
Don't sweep or vacuum droppings, urine or nests, CDC says; that can put droplets carrying viruses into the air. Put on rubber or plastic gloves first.[10]
Spray the area until very wet with a household disinfectant or a fresh bleach solution of 1.5 cups bleach per gallon of water, let it soak 5 minutes, wipe up with paper towels, and then mop or sponge hard surfaces with disinfectant.[10]
Dead mice and nests get the same soak, then go into a plastic bag that is knotted and placed inside a second bag. Wash gloved hands, remove the gloves, and wash again with soap and warm water.[10]
Common questions
- Can I release mice I catch outside?
- Relocated mice can find their way back from as far as half a mile and often die in new territory; in California it is illegal to relocate them.[1]
- How small a hole can a mouse get through?
- UC IPM says a gap about 1/4 inch tall or an opening 3/8 inch wide; CDC says a hole the width of a pencil, 1/4 inch.[1][8]
- Do ultrasonic repellers get rid of mice?
- ICWDM does not recommend them. In tests, rodents stayed away from the sound for only a few days.[6]
- Is it safe to vacuum mouse droppings?
- No. CDC says to wet them with disinfectant or bleach solution and wipe them up with paper towels instead, because sweeping or vacuuming can put virus particles in the air.[10]
Sources
- University of California Statewide IPM Program, “Pest Notes: House Mouse, Publication 7483 (revised July 2025).” ipm.ucanr.edu/legacy_assets/PDF/PESTNOTES/pnhousemouse.pdf (accessed 2026-11-11)
- University of California Statewide IPM Program, “Pest Notes: Deer Mouse, Publication 74161 (June 2012).” ipm.ucanr.edu/legacy_assets/PDF/PESTNOTES/pndeermouse.pdf (accessed 2026-11-11)
- University of California Statewide IPM Program, “Pest Notes: Rats, Publication 74106 (revised June 2024).” ipm.ucanr.edu/legacy_assets/PDF/PESTNOTES/pnrats.pdf (accessed 2026-11-11)
- iNaturalist, “Mus musculus taxon page (order and family).” www.inaturalist.org/taxa/44705 (accessed 2026-11-11)
- Internet Center for Wildlife Damage Management, “House Mice: Identification and Damage Signs.” icwdm.org/species/rodents/house-mice/ (accessed 2026-11-11)
- Internet Center for Wildlife Damage Management, “House Mouse Damage Prevention and Control Methods.” icwdm.org/species/rodents/house-mice/house-mouse-damage-prevention-and-control-methods/ (accessed 2026-11-11)
- U.S. Centers for Disease Control and Prevention, “Controlling Wild Rodent Infestations.” www.cdc.gov/healthy-pets/rodent-control/index.html (accessed 2026-11-11)
- U.S. Centers for Disease Control and Prevention, “How to Seal Up to Prevent Rodents.” www.cdc.gov/healthy-pets/rodent-control/seal-up.html (accessed 2026-11-11)
- U.S. Centers for Disease Control and Prevention, “How to Trap Up to Remove Rodents.” www.cdc.gov/healthy-pets/rodent-control/trap-up.html (accessed 2026-11-11)
- U.S. Centers for Disease Control and Prevention, “How to Clean Up After Rodents.” www.cdc.gov/healthy-pets/rodent-control/clean-up.html (accessed 2026-11-11)
- U.S. Centers for Disease Control and Prevention, “About Leptospirosis.” www.cdc.gov/leptospirosis/about/index.html (accessed 2026-11-11)
- U.S. Centers for Disease Control and Prevention, “About Hantavirus.” www.cdc.gov/hantavirus/about/index.html (accessed 2026-11-11)
- U.S. Centers for Disease Control and Prevention, “About Lymphocytic Choriomeningitis.” www.cdc.gov/lymphocytic-choriomeningitis/about/index.html (accessed 2026-11-11)
- Journal of Allergy and Clinical Immunology, via PubMed, “Phipatanakul W, Eggleston PA, Wright EC, Wood RA (2000), Mouse allergen. II. The relationship of mouse allergen exposure to mouse sensitization and asthma morbidity in inner-city children with asthma, J Allergy Clin Immunol 106(6):1075-1080.” pubmed.ncbi.nlm.nih.gov/11112889/ (accessed 2026-11-11). Cited from the PubMed abstract.