As temperatures drop, mice instinctively seek warmer, sheltered environments to survive the coming cold. The common house mouse (Mus musculus) and the deer mouse (Peromyscus maniculatus) search for structures that offer protection. Since these small rodents do not hibernate, they must find a reliable source of warmth and food to remain active throughout the winter months. This biological drive often leads them directly inside human dwellings.
Common Winter Hiding Spots
Mice seek out dark, secluded locations close to a heat source, often utilizing hidden spaces within a home’s structure. Indoors, they establish nests in wall voids, behind large kitchen appliances where motor heat is consistent, and within the insulation of attics and unfinished basements. These locations provide a thermal barrier and a low-traffic environment where they can raise their young. Their flexible skeletons allow them to compress their bodies and enter through extremely small openings.
An adult mouse can fit through any gap approximately the size of a pencil’s diameter (about one-quarter of an inch or six millimeters). Tiny cracks in the foundation, gaps around utility line penetrations, and loose seals around doors are all potential doorways. Outside, before gaining entry, mice use dense brush, woodpiles stacked close to the foundation, or deep ground burrows for temporary shelter. They can also survive in the subnivean zone, a network of air pockets beneath snow where temperatures remain near freezing but are insulated from wind chill.
Survival Needs During Colder Months
The primary factor driving mice indoors is their inability to efficiently manage body temperature in cold environments. Mice must maintain a consistently high body temperature, requiring significant and constant energy expenditure. The preferred temperature range, known as the thermoneutral point, is high, hovering between 29°C and 33°C (84°F and 91°F). This difference between their ideal temperature and outdoor temperatures greatly motivates their move to a heated indoor space.
When external temperatures drop below their thermoneutral point, their metabolic rate nearly doubles to generate heat. They rely on nonshivering thermogenesis, a process where specialized brown adipose tissue burns energy to produce heat. The high energy cost of staying warm is compounded by the scarcity of natural food sources in winter, forcing them to search for high-calorie items like stored grains, nuts, and pet food. Once inside, they create compact, softball-sized nests from shredded materials such as insulation, fabric scraps, or paper to create a thermal barrier.
Keeping Mice Out of Your Home
The most effective strategy for preventing a winter infestation is exclusion, which involves sealing all potential entry points around the home’s perimeter. Begin by inspecting areas where utility lines (gas, water, and electrical conduits) enter the house, as these spots often have small, unsealed gaps. Any hole or crack one-quarter inch or larger must be filled with materials mice cannot chew through, such as coarse steel wool or copper mesh, secured with caulk or expanding foam. For larger structural holes, use a strong, durable material like wire mesh, cement, or metal sheeting to create a permanent barrier.
Sanitation and habitat reduction further discourage mice from lingering near the home. Inside, all dry goods (including flour, sugar, and pet food) should be stored in thick plastic, glass, or metal containers with tight-fitting lids, as mice easily chew through cardboard boxes. Cleaning up food debris and crumbs immediately removes an attractive food source. Outside, remove debris piles and ensure garbage cans have secure, tightly sealed lids. Woodpiles should be moved at least 100 feet away from the foundation and elevated a foot off the ground to eliminate a common outdoor nesting site.