Norway rats are also called brown rats, sewer rats, or street rats.

Norway rats (Rattus norvegicus) are brown or dark grey with thick stocky bodies. Their bodies are 6-11 inches long, with hairless tails that are shorter than their bodies. They have smaller ears than roof rats. It may be very difficult to distinguish Norway rats from other rodent species, particularly roof rats, based on appearance alone.

Norway rats are omnivores and forage on almost anything. Pet food, fallen fruit and garbage are common attractants. All rats are neophobic (afraid of new things) and it is believed that they learn which foods are safe to eat from watching their parents or their nest mates. It’s also believed they are capable of a degree of ultrasonic communication (above our range of hearing), although how much they “tell” each other what is safe to eat or drink is unknown.

Norway rats use underground burrows and may be found on creek banks, shorelines, and sewer systems. They may dig their own burrows (usually adjacent to a structure that provides a “roof”) or use burrow systems dug by ground squirrels or other animals. The holes are usually left open but may be hidden under vegetation, garbage, or debris. Their gnawing may also cause substantial damage to house wiring and insulation.

A female Norway rat produces an average of 5 litters per year with an average of 7 pups per litter. Young Norway rats are able to reproduce when 5 weeks old. They have a maximum lifespan of three years but usually live one year or less in the wild.

Norway rats may carry different bacteria and parasites, such as those that cause rat bite fever, Weil’s disease, cryptosporidiosis, toxoplasmosis, Q fever, and trichinosis.

Norway rats originated from the plains of China and Mongolia but have adapted to live alongside humans and have been transported throughout the world. This species has been domesticated and are frequently used as laboratory animals or kept as pets.

Page last reviewed: December 28, 2023