Mice in Winter: Do They Get Worse and How to Keep Them Out

TL;DR

• Yes, usually. Cold nights often push outdoor mice indoors, and once inside, house mice can keep breeding all season.
• Mice don't go away in winter. House mice and deer mice do not hibernate, so they tend to move to the warmest protected spot they can reach, often your house.
• The mice you hear in the walls in midwinter usually got in during the fall. Openings and escaping heat draw them to a building.
• Seal openings larger than 6 mm with metal or concrete before the cold arrives, as the Government of Alberta suggests. Sealing in the middle of winter can still cut off new arrivals.
• Store dry food and pet food in metal or glass containers, and move woodpiles away from the house.
• Need help? Get a quote from a recommended local exterminator through Pest Agent's referral form.

Mice in winter usually get worse, not better: the cold you might expect to thin them out tends to push them toward the warmest, best-stocked shelter nearby, and that is often your house. Openings and escaping heat draw them to a building, and house mice that get inside can keep breeding through the season.

The timing works against you. House mice tend to move indoors in autumn, as the nights turn colder, so the mice you hear in the walls in midwinter usually got in during the fall.

Not every mouse rides out the cold the same way, and the two species most likely to end up in a Canadian home generally do not hibernate.

What Happens to Mice in Winter?

Mice in winter stay active: house mice and deer mice do not hibernate, so the cold sends them looking for shelter instead of putting them to sleep. The Canadian Encyclopedia lists many species of mice in Canada, and among the most common across the country are the house mouse, the deer mouse and the meadow jumping mouse. Each one handles winter differently, which is why you may read conflicting answers online.

Do Mice Go Away in Winter?

Mice do not go away in winter. They move. Outdoor mice either settle into a sheltered nest or find their way into a building, and mice that are already in your house have every reason to stay: heat, food and a safe place to nest. That is why mice often seem to appear out of nowhere in late fall and winter: the cold has pushed them closer to people.

Do Mice Hibernate?

Most mice do not hibernate. The Government of Alberta states that mice do not hibernate, although some species may reduce their activity during extreme winter conditions. The Canadian Encyclopedia adds that some species may stay active all winter while others hibernate. The two mice you are most likely to find in a Canadian home, the house mouse and the deer mouse, belong to the first group.

Which Mice Hibernate in Canada?

The meadow jumping mouse is a Canadian mouse that truly hibernates. According to Animal Diversity Web (University of Michigan), it usually starts hibernating around late September or early October in a nest of grass and leaves inside an underground burrow, and comes back out in mid to late spring. It needs enough body fat to make it through, so it fattens up in early fall. Jumping mice live in fields and meadows, so they are rarely the mice scratching in your walls.

How Do Deer Mice Survive the Cold?

Deer mice survive the cold by sharing heat and saving energy. Animal Diversity Web reports that in winter, groups of deer mice may huddle together in one nest, and that they can enter a daily torpor, a short state where body temperature drops to conserve energy. In cooler climates, deer mice may also stash food in the autumn. When a warm building is close by, such as a cottage, shed or house near a field or woods, Health Canada notes they may move in during the fall.

How Do House Mice Survive the Cold?

House mice survive the cold by living with people. The house mouse is not native to North America: The Canadian Encyclopedia notes it likely arrived with the first colonists, and Alberta Agriculture says it often depends on people for shelter and food, particularly in cooler climates. In practice, a house mouse in a Canadian winter is almost always in or around a building, which is why it is the mouse you are most likely to meet indoors.

Where Do Mice Go in Winter?

Mice in winter go to the warmest protected spot they can reach: underground burrows, outbuildings, or the inside of your house. Where a mouse ends up depends on its species and on how close it lives to people.

Outdoor Burrows and Nests

Outdoor burrows and nests shelter the mice that stay outside. Deer mice in wooded areas often nest near the ground in stumps, logs and brush piles, and meadow jumping mice usually sleep through winter in burrows underground. These mice are not a problem as long as they stay outdoors, but brush piles and woodpiles right against your house give them a staging point next to your walls.

Sheds and Cottages

Sheds and cottages are prime winter shelter because they are dry, quiet and nobody disturbs them for months. Animal Diversity Web notes that deer mice may nest in cottages and outbuildings, and the Public Health Agency of Canada lists garden and storage sheds among the places where people come in contact with rodents. If you close a cottage or shed for the season, it helps to seal it and remove food before you leave. Attached garages raise the same issue, because they are often the easiest way into the house.

Inside Your House

Inside your house, mice head for dark, undisturbed spots close to food and warmth: wall voids, attics, basements, crawl spaces and the space under appliances. The University of Nebraska-Lincoln notes that mice often live in stacked wood, debris and insulation, and that they build nests from shredded paper or other soft material (UC IPM).

Vehicles

Vehicles parked for the winter can also shelter mice. UC IPM warns that house mice can damage vehicles by gnawing on electrical wires. If your car sits unused in a garage or driveway for long stretches, check under the hood and the air filter area from time to time, and read what to do about mice in your car.

Why Are Mice in the House Worse in Winter?

Mice in the house get worse in winter because cold nights push outdoor mice indoors, and once inside, house mice can keep breeding all season. At the same time, more of them means more chewing and more contamination.

Falling Temperatures

Falling temperatures are the trigger. UC IPM explains that where outdoor house mice exist, they frequently enter homes in autumn when nighttime temperatures become colder, and Health Canada notes that deer mice may invade buildings near fields and woodlands in the fall.

Escaping Heat

Escaping heat guides mice to your openings. The University of Nebraska-Lincoln says mice are often attracted to buildings when they detect openings and escaping heat. Every gap that leaks warm air in January, around a pipe, a vent or a door, is also a signpost for a mouse outside.

Food and Shelter Indoors

Food and shelter indoors keep mice from leaving. The Government of Alberta notes that mice can thrive in close association with people wherever food, water and shelter are available. A pantry, a pet food bag, crumbs under the toaster and a warm wall cavity give a mouse everything it needs in one place, and house mice seldom travel far from their nest and food (UC IPM).

Year-Round Breeding

Year-round breeding is what turns a couple of winter visitors into an infestation. Most wild mice typically breed from spring to autumn, but house mice can reproduce throughout the year (The Canadian Encyclopedia). According to UC IPM, a female house mouse may have 5 to 10 litters a year of about 5 or 6 pups each, and the young are mature 5 to 6 weeks after birth.

Chewed Wires

Chewed wires are the most serious damage mice cause indoors. The Government of Alberta warns that their habit of chewing on electrical wiring presents a serious fire hazard, and UC IPM notes that many fires of unknown origin are believed to be caused by rodents gnawing on wires. Mice also gnaw wood, drywall and insulation, and they chew into storage boxes and food packages.

Health Risks

Health risks come from droppings, urine and contaminated surfaces. Health Canada states that mice and rats are carriers of disease, and that the deer mouse is the most common carrier of the deadly hantavirus. House mice are not known to carry hantavirus (University of Nebraska-Lincoln), but most people cannot tell the two apart, so treat every cleanup with care. Research from Johns Hopkins also links mouse allergens in homes to more severe asthma in children.

Mice do not disappear in the warm months either: see whether mice can invade your home in summer. And if it feels like you have more mice than usual, read why mice are so bad this year.

What Are the Signs of Mice in Your House in Winter?

Mice in your house in winter usually give themselves away at night, through sounds, droppings and chewed food packages. The signs often show up before you ever see one, since all mice are mostly active at night. For the complete list, see our guide to the signs of a mouse infestation.

Scratching Sounds at Night

Scratching sounds at night are often the first winter sign. Health Canada lists scampering and scratching sounds in the walls at night, and the University of Nebraska-Lincoln mentions scratching and squeaking from ceilings and walls. Listen near exterior walls, the attic hatch and behind the fridge or stove.

Droppings

Droppings are often what people find first, according to the University of Nebraska-Lincoln. Look in kitchen drawers, cupboards, under the sink and along baseboards.

Gnaw Marks

Gnaw marks on food packages, cardboard, wood or wiring are a strong sign of mice. Health Canada lists signs of gnawing or chewing and damaged food packages among the clues to watch for.

Musky Odour

A musky odour is often noticed where house mice have been present for a long time (University of Nebraska-Lincoln). A stale, musty smell in a closet, cupboard or basement corner often points to a nest nearby.

Daytime Sightings

Daytime sightings are a warning sign. House mice are active mostly at night but can be seen occasionally during the day (UC IPM), and the Government of Alberta notes that repeated daytime sightings can point to a larger or well-established infestation.

How Do You Keep Mice Out in Winter?

Keeping mice out in winter means closing every opening larger than 6 mm before the cold arrives and removing the food that makes your house worth the trip. Fall is the best time to do it, but sealing gaps in the middle of winter still cuts off new arrivals. For a full year-round plan, read our guide on how to keep mice out of your house.

Seal Gaps Before the Cold

Sealing gaps is the most effective step. Health Canada says mice can squeeze through cracks as small as a dime, and the Government of Alberta recommends sealing openings larger than 6 mm with durable, gnaw-resistant materials such as metal or concrete. Check the foundation, siding, the spots where pipes, cables and the dryer vent go through the wall, and the gaps around the garage door. Our guide on how to find mouse entry points walks you through a full inspection.

Doors and Windows

Doors and windows need a tight seal at the bottom and sides. Health Canada recommends metal weather stripping under doors and weather stripping on windows. Check the door that leads from the garage into the house too, since garages are often less tightly sealed.

Vents and Pipes

Vents and pipes are easy entry points. Health Canada advises stuffing steel wool around pipes before caulking or plastering, and covering dryer vents, attic vents and soffits with fine mesh metal screening. For larger gaps, pack steel wool or wire mesh into the opening first, then seal it with caulk or foam.

Food Storage

Food storage removes the reason mice stay. Health Canada recommends storing dry food and dry pet food in metal or glass containers and keeping garbage in containers with tight-fitting lids. Wipe up crumbs, do not leave pet food out overnight, and move bird seed into a sealed bin.

Firewood

Firewood stacked against the house is a ready-made mouse shelter right next to your walls. Health Canada suggests raising woodpiles about 30 cm (1 foot) off the ground, and the Public Health Agency of Canada advises moving woodpiles and compost bins away from buildings. Bring in only the wood you will burn soon, and check each armful before it comes inside.

Trapping Mice Already Inside

Trapping is the safest way to deal with mice already inside. Health Canada says snap traps and electronic traps are easy to use and very effective if they are well positioned and set properly. Place them along walls and known travel routes (Government of Alberta), behind objects, in dark corners and where you found droppings, no more than about 10 feet (about 3 metres) apart (University of Nebraska-Lincoln). Our picks for the best mouse traps can help you choose.

If you use poison bait, Health Canada says it must go in a tamper-proof bait station wherever children and pets can reach, warns that anticoagulants are usually highly toxic, and advises against using baits as the only method. Always follow the label. For a complete plan, see how to get rid of mice.

Safe Cleanup

Safe cleanup protects you from the germs in droppings and urine. The Public Health Agency of Canada advises wearing rubber or plastic gloves, never sweeping or vacuuming droppings, and soaking the area with a Health Canada-approved disinfectant or a mix of 1 part bleach to 9 parts water for 10 minutes before wiping it up with paper towels. The Government of Alberta recommends airing out the space for at least 30 minutes first. This matters most when you open a cottage, trailer or shed after the winter. Our guide on how to clean mouse droppings has the full steps.

When to Call a Pest Control Professional

A pest control professional is worth calling when you keep catching mice week after week, when you hear activity in several rooms or in the walls, or when you cannot find how they are getting in. Health Canada notes that commercial class rodent products must be applied by a certified professional. Learn how to find a mouse pest control professional, and if you want help, you can get a quote from a recommended local exterminator through Pest Agent's referral form. If you rent, read who is responsible for mice in a rental property in Canada.