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Signs of a Bad Mice Infestation

Signs of a bad mouse infestation include droppings and strange sounds in your walls. Read our guide to learn more about what you should look for and how to keep mice out.

Default Author Icon Written by This Old House Reviews Team Updated 06/20/2024

Mice can destroy insulation, chew through electrical wiring, and lead to serious illness. If you suspect a mouse infestation, take action quickly to avoid further property damage and sanitation concerns. In this guide, we’ll cover the early telltale signs of a bad mouse infestation, provide tips to help you treat the problem immediately, and offer prevention measures to keep mice away.


Identifying Signs of a Bad Mice Infestation

Mice move quickly and hide in small, dark spaces, so it can be hard to spot signs of a mouse infestation. However, two undeniable signs that mice have moved into your home include mouse droppings, often found in your attic, basement, or around entry points, and scratching noises behind your walls.

Mouse droppings are roughly a quarter of an inch and look like dark brown or black granular pellets. You may notice droppings in your kitchen, pantry, or other areas where you store food. If you don’t see any pellets, listen for common mouse noises such as scratching, scurrying, chirping, and squeaking. If you have pets, you may notice them sniffing around areas where they detect the scent of mice and listening for sounds of scampering and squeaking.

If you notice any of these signs, take steps to address the issue immediately. Mice breed quickly and, if left to their own devices, can quickly take over your home and cause structural damage.


Common Types of Mice

Most mice look the same from a distance, but there are three distinct varieties that can make their way inside your home and become a nuisance.

Deer Mouse

You can identify a deer mouse by its round shape, bulging eyes, and large ears. It tends to be brown with white feet and a white underbelly, and it has a bicolored tail that’s half brown and half white. Deer mice have short life spans, often living in the wild for no longer than a year and in captivity for up to eight years. They breed rapidly, with one female capable of producing several litters a year.

House Mouse

House mice have pointed snouts, hairless tails, and large, rounded ears. They tend to be gray or light brown and smaller than deer mice. House mice are mostly nocturnal and are averse to bright light.

White-Footed Mouse

This is also called a “woodmouse.” A white-footed mouse has a long tail, large ears, and a brown back with a white belly. These mice can live for up to several years in the wild. They tend to avoid humans whenever possible but can take up residence in homes, favoring ground-floor walls for their nests. This species can carry hantaviruses, which cause severe illness in humans.


Mice vs. Rats: Understanding the Difference

Mice and rats are both rodents that can cause serious infestations. However, there are a few distinct differences between these pests.

Pest TypeMiceRats
Common FeaturesMice have large, droopy ears and long, often-scaly tails. They typically have brown, white, or gray coats and pointy snouts.Rats have smaller ears than mice and long, hairless tails that look pink. They have blunt snouts and white, black, brown, or gray coats.
Signs of InfestationMice leave behind more droppings than rats. Their droppings are about a quarter inch in size and have pointed ends. Mice nests are usually composed of soft, shredded material and live on any level of your home.Rats leave fewer droppings and tend to avoid people and traps. Rat droppings are about three-quarters of an inch and have blunt ends. They often inhabit lower levels of dwellings.
Regions Commonly FoundMice live all across North America. They’re prevalent in rural, suburban, and countryside locations.Rats live all across North America. They prefer urban locations and are common in large cities and suburban areas.

Health Risks Associated With Mice Infestations

A serious infection or illness due to a mouse infestation is rare, but it can occur. Mice can bring fleas, ticks, and mites into your home, which carry illnesses such as Lyme disease. Mice are also direct carriers of diseases such as leptospirosis, hantavirus, Lassa fever, and lymphocytic choriomeningitis. Mice can bite humans when cornered, but this behavior isn’t common.

The best way to safeguard against these illnesses is to take action quickly if you notice any signs of a mouse infestation, such as a dead mouse, mouse feces, or an ammonia-like smell that could indicate the presence of mouse urine.


Damage Caused by Mice Infestations

Both rats and mice can cause structural damage to your home. Mice chew on almost anything they can use to build nests, including wood, cloth, books, insulation, and furniture. They’ll also burrow into furniture to create their nests and can invade crawl spaces to form nests in your insulation. Mice have been known to settle in electrical appliances, causing appliances to short-circuit.

Mice will feed on various food items, from pet food to dried goods like beans and oats. They’ll gnaw through packaging, ruining the food item and making a mess in your pantry or kitchen. These rodents will contaminate your space by leaving behind poop, urine, and mouse hair.


Dealing With a Bad Mice Infestation

Swift action is key to getting rid of mice or rats in your home and preventing further issues. You have options for dealing with a bad mouse infestation, including do-it-yourself (DIY) methods or investing in a mouse exterminator.

DIY Methods for Mice Control

Hiring Professional Pest Control Services

DIY methods include sealing any obvious cracks or holes where rodents could be entering the house with caulk. You should also secure any food sources by storing dried goods and pantry items in glass containers, and set out mouse traps where you’ve seen mice, nesting materials, or droppings.

There are various traps available, including humane traps, snap traps, electric traps, and bait traps. Humane traps allow you to release the mouse into the wild after you’ve caught it. Bait stations have poison baits that will kill mice over a few days. Always exercise caution when using mouse traps, especially if you have pets or small children.

Pest control services are often the best way to handle a mouse infestation. A professional exterminator can deploy various methods to kill or remove the mice, depending on your infestation level. A pest control company can also effectively investigate crawl spaces and other areas difficult for homeowners to access.

Keep the following tips in mind when trying to find the best pest control service:

  • Ask if the company guarantees its work and will re-treat the issue if mice infest your home in the future.
  • Ensure the company is licensed and determine if its employees are bonded. If they are, the company will reimburse you for any loss or damage caused by the employee.
  • Request a quote from three pest control providers to compare treatment pricing.
  • Spend some time researching various providers online and reading third-party reviews.


Our Conclusion

Mice can negatively affect your home and well-being. You must take action quickly if you see signs of a mouse infestation, such as droppings, mouse nests, or gnaw marks on baseboards or entry points. You can use DIY methods to get rid of mice, but a professional exterminator is usually the most effective way to get rid of a bigger infestation. A pest control company can quickly diagnose the problem and use a customized solution to tackle your mouse problem at the source.


FAQ About Signs of Bad Mice Infestation

How do you know if you have a serious mouse infestation?

You know you have a serious mouse infestation if you see a lot of mouse droppings or gnaw marks on furniture or baseboards, you hear scampering, scurrying, or squeaking from within your walls, or you see physical mice around your home. You may also notice your cat or dog sniffing around your walls or crawl space.

How many mice in a house is considered an infestation?

There’s not a set number of mice in a house that’s considered an infestation. If you have just one or two mice in your home, they could breed quickly and produce dozens of mice. Address the problem as soon as you notice it so you don’t have to deal with a full-blown infestation.

How do I find a mouse nest?

Look in small, dark spaces such as your attic, basement, or crawl spaces to find a mouse nest. The nest will look like a 3- to 6-inch pile composed of fabric, paper, sticks, or bedding. You can also find mouse nests in sheds or outdoor areas.

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