The term “gray mice” refers to the common house mouse, Mus musculus, a small rodent found globally, closely associated with humans. Highly adaptable, these creatures have spread across continents, thriving in diverse environments wherever human activity provides shelter and food. Their widespread presence makes them one of the most common rodent pests encountered by people.
Identifying Common Gray Mice
House mice have a slender body, measuring between 6 to 11 centimeters (2.4 to 4.3 inches) with their tail often matching their body length. Their fur color varies from light brown to shades of gray, sometimes appearing nearly black, with lighter underparts. They have large, thinly furred ears and small, dark, protruding eyes. Their long, slender, nearly hairless tail, which appears scaly, is a distinctive feature.
Their Habitat and Behavior
House mice are highly adaptable, inhabiting both indoor and outdoor environments. Indoors, they reside in homes, commercial buildings, wall voids, cabinets, attics, and garages, seeking dark, secluded nesting sites. Outdoors, they construct nests in fields, gardens, and beneath trees or shrubs. They are primarily nocturnal, most active at night, though they may be seen during the day, especially with larger populations. They are agile climbers and jumpers, constantly exploring their surroundings and memorizing pathways, food sources, and shelter.
They build globular nests, 4 to 6 inches in diameter, using shredded paper, cotton, wall insulation, and other fibrous materials. These nests are often situated near heat sources like compressors or water heaters. They can squeeze through openings as tiny as a dime-sized crack to gain entry. Their presence is often detected by a characteristic musky odor.
Diet and Reproduction
House mice are omnivorous, consuming a wide variety of foods, preferring seeds and grains. They are opportunistic feeders, nibbling on human food scraps, including items high in fat, protein, or sugar. While a single mouse eats about 3 grams of food per day, their habit of sampling many items and discarding partially eaten portions means they contaminate significantly more food than they consume. House mice can obtain sufficient water from their food, though they will drink when water is available, even lapping condensation.
Their reproduction is rapid and prolific. After a gestation period of 19 to 21 days, females produce litters of 5 to 6 young, though litters can range from 5 to 12. A single female can produce 5 to 10 litters per year, and under optimal conditions, a population can grow quickly. Newborn mice are hairless with closed eyes, but develop rapidly, becoming covered with hair and opening their eyes within two weeks. They begin exploring and eating solid food around three weeks of age and reach sexual maturity as early as 6 to 10 weeks old.