Brown Rat (Rattus norvegicus)

Brown Rat overview

The brown rat, also called the Norway rat, is the common rat of cities, sewers and farms and one of the most widespread mammals on Earth. Despite the name it has nothing to do with Norway; it probably originated in northern China and reached Europe in the 1700s, then spread worldwide on ships. It is a stocky, burrowing rat, larger and heavier than the black rat, with a blunt muzzle, small ears and a tail shorter than its body. Brown rats are intelligent, social and wary of new objects. Pet 'fancy' rats and laboratory rats are domesticated forms of this species.

How Long Do Brown Rats Live?

Brown rats live about 1–2 years in the wild, and most die before their first birthday. Pet and laboratory rats usually live 2–3 years and occasionally reach four. Predators, poison, traps, disease and fighting account for the short lives of wild rats.

How Much Does a Brown Rat Weigh?

Adult brown rats weigh 200–500 g (7–18 oz). Males average around 350 g and females around 250 g. Rats heavier than 500 g are unusual in the wild, and stories of cat-sized sewer rats are exaggerations, although well-fed pet males can reach 700–800 g.

How Long Is a Brown Rat?

A brown rat has a head-and-body length of 20–28 cm (8–11 in), plus a scaly tail of 17–23 cm that is slightly shorter than the body. A shorter tail, smaller ears and a blunter nose distinguish it from the slimmer black rat.

How Fast Can a Brown Rat Run?

Brown rats are commonly said to run at about 13 km/h (8 mph) in short dashes. They are better known as swimmers and climbers: they can tread water for days in laboratory tests, swim through sewer pipes and jump about 1 m horizontally.

How Long Is a Brown Rat Pregnant?

A brown rat is pregnant for 21–24 days. Litters usually contain 6–12 pups, and a female can mate again within hours of giving birth, producing up to five or more litters a year. Young rats can breed at about five weeks old in good conditions.

What Do Brown Rats Eat?

Brown rats are omnivores that eat almost anything, including grain, garbage, meat, eggs, insects and fish, and they need water daily. They are cautious about unfamiliar food and sample tiny amounts first, which is why they are hard to poison.

Diet type: omnivore. Almost anything: grain, seeds, fruit, garbage, pet food, meat scraps, eggs, insects, snails, fish, and the chicks and eggs of ground-nesting birds. Cereals are preferred where available.

Where Do Brown Rats Live?

Brown rats live wherever people provide food and shelter: sewers, basements, warehouses, farms, docks and dumps on every continent except Antarctica. They are burrowers that prefer ground level and damp places, and in mild climates they also live along riverbanks, ditches and coasts.

Are Brown Rats Endangered?

Brown rats are listed as Least Concern on the IUCN Red List and are abundant worldwide. They are a serious pest and one of the most damaging invasive species on islands, where they eat seabird eggs and chicks. Eradications have cleared them from islands such as South Georgia and Campbell Island.

Least Concern

Brown Rat fun facts

• Rats make ultrasonic chirps when they are tickled or playing, which researchers have compared to laughter.
• A brown rat's incisors grow about 10–12 cm a year and are hard enough to gnaw through wood, plastic, lead pipe and soft concrete.
• Laboratory experiments have shown that rats will free a trapped companion even when they could have a chocolate treat to themselves instead.
• The oft-quoted claim that there is one rat per person in cities is a myth; careful estimates for New York put the figure at far fewer.
• Alberta, Canada, has kept itself essentially free of breeding brown rats since the 1950s through a government control program.

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Brown Rat FAQ

Related animals

All mammals