Norway Rat

Rattus norvegicus

Last updated: May 27, 2024
Verified by: AZ Animals Staff
Holger Kirk/


Norway Rat Scientific Classification

Scientific Name
Rattus norvegicus

Read our Complete Guide to Classification of Animals.

Norway Rat Conservation Status

Norway Rat Facts


Norway Rat Physical Characteristics

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The Norway rat or brown rat is native to China, but due to human travel, they have been able to access ships and populate every continent except Antarctica. As a result, these rats are currently the most common in North America and occupy our cities, farmlands, and even our homes.

Identifying a Norway Rat

The Norway rat has coarse fur, usually brown or dark grey. Similarly, their bellies are generally light grey or brown. These brown rats grow to eight or 10 inches, with their tails adding another seven to 10 inches to their overall length. Essentially, their bodies and tails are more or less the same lengths. Adult males achieve weights of approximately 12 ounces, while adult females reach about 9 ounces. Some reports show Norway rats growing much bigger and weighing in at between 32 to 35 ounces.

Because of global sightings of massive rats, some people believe that common species such as the Norway rat can develop to similar sizes as house cats. However, this rat species cannot reach this size and is often the prey of house cats. Instead, rodents that achieve similar proportions to the standard house cat are the coypu or the muskrat rather than rat species with which city dwellers are familiar.

Activity and Senses

The Norway rat is a nocturnal mammal and becomes active at dusk. They spend most of their busy time looking for food and water. Although these rodents are nocturnal, they will also become active during the day when rat populations are high, increasing the competition for food. This behavior is more typical in cities and crowded suburban areas.

Norway rats do not have the best eyesight and are color-blind. Because of this, they must depend on their other senses, like hearing, smell, taste, and touch, to move around and find food sources. However, the Norway rat’s sense of smell is powerful, picking up food contaminants at levels as low as 0.5 parts per million.

Their Nests

Norway rats tend to build their nests at or below ground level. They burrow or find spaces underneath porches or the home’s foundation to build their nests. They frequently make their nests from man-made materials like shredded paper, cloth, or other fibrous materials.

Their nests are also generally found near water sources. And their love of water has earned them the nickname ‘water rats’ as they are excellent swimmers. Besides, Norway rats prefer living near water for survival, to find food, and to use water bodies as travel routes. Moreover, people have records of these rats swimming distances of more than 2,000 feet, indicating how comfortable they are in and around water.

Reproductive Cycles of Norway Rats

These rats reach sexual maturity at 11 weeks. After reaching sexual maturity, they can mate and become pregnant, and their gestation period lasts from 21 to 24 days. When the doe, a female rat, gives birth, she often gives birth to a litter of seven to eight rat pups.

Rat pups are born blind and without fur. Therefore, they depend wholly on their mother, who keeps them warm and feeds them until they are strong enough to leave the nest. Rat pups usually leave the nest two weeks after being born and can eat solid foods at this time. Norway rats are known to produce three to five litters annually.

Norway Rat Diet

A wide range of foods is acceptable to these rats since they are foragers. A study examining the contents of a rat’s stomach found that it consumed over 4,000 different food items. Because of this dietary diversity, Norway rats have been able to thrive all over the planet and populate all continents except Antarctica.

In the city and urban areas, these rats generally eat discarded food on garbage heaps. Additionally, this species tends to invade homes to eat human food or crops when living in suburban and farm areas. Norway rats typically eat plants and protein sources in the wild. These rats will even hunt and are known to prey on fish, lizards, baby birds, and other smaller rodents.

Pet Norway rats obviously have a better diet than those in the wild. Pet rats eat rat feed and pellets that owners buy from pet shops, with fresh vegetables, seeds, nuts, pasta, fruit, and yogurt being recommended delicious treats.

Social Behavior of Norway Rats

If they have the chance, Norway rats will live in groups growing to hundreds of members, called colonies. When they do, they build social relations. The colonies often have one adult male with a few females for mating. Norway rats locate their colonies in specific territories, marking the area with scent cues. The adult males will protect their colonies and territories by fighting if necessary.

Although rats fight to protect settlements, they can be friendly when meeting a new rat. When new rats meet, they examine and get to know each other by smelling their scent to determine their age, health, and if they are on heat.

Young rats are also known to play-fight and groom each other. Rats in colonies sleep in groups and cuddle to stay warm. They learn from each other about their food habits, preferences, and specific food quality by sniffing the mouth and fur after they finish eating.

Diseases Carried by Norway Rats

All rats are known to be disease carriers and have caused major pandemics across the globe over the past few centuries. Norway rats carry pathogens that can infect humans and animals, like:

  • Weil’s disease
  • Rat bite fever
  • Cryptosporidiosis
  • Viral hemorrhagic fever
  • Q fever
  • Hantavirus pulmonary syndrome
  • Toxoplasmosis

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About the Author

I'm a freelance writer with more than eight years of content creation experience. My content writing covers diverse genres, and I have a business degree. I am also the proud author of my memoir, My Sub-Lyme Life. This work details the effects of living with undiagnosed infections like rickettsia (like Lyme). By sharing this story, I wish to give others hope and courage in overcoming their life challenges. In my downtime, I value spending time with friends and family.

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