In the United States, Norway rats live throughout the lower 48 states. While generally found at lower elevations, this species can occur wherever people live. The Norway rat is not really from Norway — they are believed to have originated in China.
Norway rats, also called brown or sewer rats, are large, burrowing rodents that are larger than roof rats. They are generally bulky with coarse shaggy brown to grey colored fur with gray to grayish brown underbellies. These types of rats can weigh 7 to 18 ounces and reach lengths of about 16 inches – their tails alone may measure more than 8 inches. The tails are scaly and shorter than the length of the head and body combined. Their ears are small, scaly, and have no fur. Droppings are capsule-shaped.
Norway rats typically nest in underground burrows typically found along building foundations, beneath rubbish or woodpiles, and in moist areas in and around gardens and fields. Nests can be lined with shredded paper, cloth, or other fibrous material. They usually enter buildings in search of food. When searching for food and water, Norway rats usually travel an area of about 100 to 150 feet in diameter; seldom do they travel any further than 300 feet from their burrows or nests. The average female Norway rat has 4 to 6 litters per year and can successfully wean 20 or more offspring annually. When Norway rats invade buildings, they usually remain in the basement or ground floor.
Norway rats are omnivorous and feed on a variety of food sources. They prefer meats, fruits, grains and nuts, and some fruits but will really eat anything. Dead animals also serve as a food source for these rats, and they are capable of catching small fish and rodents. They require water to drink, and they make their colony as close to a water source as possible. They have limited agility, but are excellent swimmers.