What You Need to Know About the House Mouse

A house mouse against a wall

Barrie Watts / Photodisc / Getty Images

Some mice can make cute, fun pets, but the house mouse is not one of those. And when a rodent creeps into your home through a crack or gap or gnaws on drywall, stored boxes, and paper, or even wiring to make its nest—while urinating and dropping feces as it travels, it can be a danger and health hazard to your family.

But because mice are small, nocturnal, and nest in out-of-the-way places, you may not even know you have a problem until the population gets large and you have a major problem.

So, how do you know if you have mice? And why are they a health problem? The following provides a guide to house mouse identification, behavior, disease and damage, and signs.

Mouse Identification

Small, with a slender body, its physical characteristics include:

  • Body length: 2 - 3 1/4 inches
  • Tail: 3 - 4 inches long and hairless
  • Weight: less than 1 ounce
  • Color: usually light brown to gray
  • Head: small with small black eyes, pointed snout and large ears

Mouse Behavior

  • Mice are nocturnal, meaning they are most active at night—when most of your family is asleep.
  • It is so flexible that it can get into your home through a crack or hole as small as 1/2-inch.
  • A mouse can jump as high as a foot, and jump downward as much as 8 feet.
  • It can swim well and travel upside down clinging to 1/4 inch wire.
  • Being very inquisitive, a mouse will nibble or feed on any available human food, as well as other household items, such as paste, glue or soap.
  • It does not need free water but can survive on the water in the food it eats.

Mouse Signs

Although mice will rarely run in the open during the day (unless you have a major infestation), they do leave signs of their presence. Look for:

  • Dead or live mice.
  • Nests or piled nesting materials.
  • Gnawed holes in stored foods, piled papers, insulation, etc.
  • Food scraps or wrappings left behind.
  • Excreted droppings—1/4-1/8 inch with pointed end or ends.
  • Rodent hairs.
  • Runways—indicated by narrow pathways where dust and dirt have been swept clean, grease marks are noticeable, urine trails seen under black light.

You might also:

  • Hear it skittering on hardwood or laminate floors.
  • Smell the fetid odor of a large infestation.

Disease and Damage: Why Are Mice a Problem?

According to the CDC, mice and rats spread more than 35 diseases directly to humans through handling; contact with rodent feces, urine, or saliva; or rodent bites. Humans can also contract diseases carried by rodents indirectly, through ticks, mites, or fleas that have fed on an infected rodent.


A few of the diseases that can be carried or transmitted by mice are:

  • Salmonellosis
  • Rickettsialpox
  • Leptospirosis
  • Rat-bite fever
  • Lymphocytic chorio-meningitis (aseptic meningitis, encephalitis, or meningoencephalitis)
  • Tapeworms and ringworm-causing organisms

Mice are also a problem because of the damage and mess they leave behind.

  • They have no bladder control, so they trail urine wherever they walk.
  • Mice leave behind 50 to 75 droppings each day.
  • A single female mouse can reproduce up to 35 young each year.
  • They cause structural damage through gnawing and nest-building.
  • Mice feed on and contaminate foods with urine, droppings, and hair.
  • In the U.S., mice and other rodents cause billions of dollars in damage each year.

Mouse Control

Now that you know how to tell if you have mice and the problems they can cause you'll need to rodent-proof your home.

Article Sources
The Spruce uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Rodents. Centers for Disease Control and Prevention.

  2. Diseases Directly Transmitted by Rodents. Centers for Disease Control and Prevention, 2017.

  3. Phipatanakul, Wanda et al. Environmental Assessment and Exposure Reduction Of Rodents: A Practice ParameterAnnals Of Allergy, Asthma & Immunology, vol 109, no. 6, 2012, pp. 375-387. American College of Allergy, Asthma, and Immunology, doi:10.1016/j.anai.2012.09.019