They forage along narrow surface runways from their nesting areas to their sources of food. In addition, they travel and feed underground via old mole tunnels. The bark and roots of young trees are gnawed and severely damage by mice. Ripening tomatoes, cucumbers, beans, peas and other fruit close to the ground are bitten into. Developing roots or tubers of potatoes, carrots, beets and parsnips are dug into and eaten by mice, as well.
Mice often invade homes or sheds in the fall.
In wintertime, their runways are made below the snow cover where they dig up and eat seeds, nuts and bulbs. They feed on tender bark and foliage of shrubs, roses and small fruits such as blueberry. They spend the winter as a family group in a nest made of stems, leaves, sticks and roots and lined with fur, feathers or shredded cloth. Nests are found underground or in protected areas such as old burrows, under boards, hollow logs or buildings. Breeding occurs from spring to fall, with two to four litters of one to eight young per year.