Rodents - The term "commensal" means "living with or in close association to humans." Although many species of rodents occasionally may be found around humans, the term commensal rodents refers specifically to mice and rats. Norway rats, roof rats and house mice are not a native species in North America, but were transported from Europe to the U.S. during colonial settlement. House mice are nocturnal, although in some areas they may be active during the day. House mice often burrow into and nest in the ground or under structures when other shelter is not available. In most areas, the beginning of cold weather in the fall will cause rodents to search for shelter in houses, sheds and garages, warehouses and other structures. These structures can support very large populations of mice if control measures are not taken. Rodent nests are constructed of fibrous material that may include paper, burlap, or fabric and often are found under floors and in the walls of buildings. Rodents are extremely prolific and breed year-round. Mice, like Norway and roof rats are nocturnal animals that become active at dusk, when they begin to seek food and water.