Norway rats, also known as brown rats or sewer rats, are common and highly adaptable rodents found across the globe. Characterized by their stocky build and coarse fur, they thrive in diverse environments, often in close proximity to human populations.
Global Distribution and Historical Origin
Despite their common name, Norway rats did not originate in Norway. Their native range is believed to be in Central or East Asia, specifically the plains of northern China and Mongolia. These rodents began spreading to other parts of the world around the Middle Ages, with their arrival in Europe occurring by the 18th century.
Their global dispersal was largely facilitated by human activity, as they traveled as stowaways on ships along trade routes. They reached North America between 1750 and 1775, and today, Norway rats are found on every continent except Antarctica.
Preferred Habitats and Environments
Norway rats are strongly associated with human activity, and their preferred habitats reflect this. In urban areas, they commonly inhabit subterranean infrastructure like sewers, basements, and cellars. They are also found in warehouses, stores, slaughterhouses, docks, and around residences. These rodents typically prefer the lower floors of multi-story buildings, though they can climb.
In addition to urban areas, Norway rats thrive in rural settings. They frequently infest farms, including barns, granaries, livestock buildings, and silos. They also occupy agricultural fields, wooded areas, and vacant lots. Their presence is often noted near waterways like stream banks, ponds, rivers, and wetlands, as they are excellent swimmers.
These rats are burrowing animals, constructing extensive underground networks. Their burrows, typically 2 to 3 inches in diameter and up to 6.5 feet long, are found under buildings, concrete slabs, and along foundations. Nests, often lined with shredded paper or cloth, are created within these burrows or in secluded nooks, basements, and crawl spaces.
Factors Influencing Their Presence
Their widespread distribution and adaptability are attributed to several environmental factors. Food availability is a primary determinant of their presence. As omnivores, they consume nearly any type of food, preferring cereal grains, meats, fish, nuts, and fruits. They readily access human-generated waste, pet food, and agricultural products.
Access to water is another significant factor. Norway rats require approximately 0.5 to 1 ounce of water daily when consuming dry foods. They are drawn to leaky pipes, standing water, open drains, and natural bodies of water, including sewers.
Shelter and harborage are also essential. They utilize dense vegetation, cluttered areas, structural voids, and debris or woodpiles for nesting and hiding from predators. Their burrowing behavior provides secure nesting sites where females can raise their young.
Norway rats demonstrate remarkable climate adaptability, thriving in a wide range of temperatures. While common in temperate zones, they can also adapt to tropical climates. In colder regions, they often seek warmth by nesting near heat sources or moving into buildings during the colder months.