Rat

Rats kept as pets are fancy rats, a domesticated form of the brown rat (Rattus norvegicus domestica). Wild brown rats are usually brown or dark grey with lighter underparts, while fancy rats come in many coat patterns and styles.

Rats are large for rodents. The head and body can reach up to 28 cm, with a tail slightly shorter than that. Adults weigh between 140 and 500 g, and big individuals of up to 800 g are mostly seen among domestic ones.

Rats are kept as pets in many parts of the world. Fancy rat associations exist in countries including the United Kingdom, Australia and the United States, setting standards, running events and promoting responsible ownership.

Rats are thought to have originated in northern China and Mongolia, spreading to other parts of the world in the Middle Ages along routes of human migration. Reliable reports place them in England by 1730 and widespread across Europe during the Industrial Revolution.

Despite the name Norway rat, they did not come from Norway. The name was probably popularised by the naturalist John Berkenhout in 1769. They were also once called Hanover rats.

Selective breeding produced the fancy rat as well as the laboratory rat. Colour variants among domesticated rats were recorded in 18th-century Japan and 19th-century Europe. The pink-eyed white laboratory rat was bred from white-marked rats rescued from the now-outlawed sport of rat baiting.

Today's types include Hairless and Rex coats, plus dwarf and tailless rats.

Rats are social animals. They groom one another, sleep together in group nests and huddle for warmth. They form dominance hierarchies, and groups often play fight with jumping, chasing, tumbling and boxing.

Brown rats are nocturnal and good swimmers, and rats burrow when given suitable material, though domesticated laboratory rats struggle more with digging and swimming than wild rats. Rats have sharp hearing and a very well developed sense of smell, but poor eyesight.

Rats communicate in many ways. Their ultrasonic chirping, which humans cannot hear unaided, happens during play and when tickled and is likened to laughter. Pet owners sometimes use bat detectors to hear it. Teeth-grinding, called bruxing, is the most commonly heard sound and is usually triggered by happiness, though it can also be self-comforting when stressed. Vigorous bruxing can come with boggling, where the eyes bulge and retract.

The maximum lifespan of a rat is about three years. Wild rats mostly barely manage one, largely due to predators and conflict.

Rats can carry several pathogens that cause disease in people, though the information on this is mostly about wild brown rats.

Albino rats have poorer eyesight than pigmented ones. Rats that feel ill may crawl under their companions, which is thought to help them breathe, and elderly rats are often groomed and nursed by companions.

This is general awareness only, not veterinary advice. Always consult a vet about your pet's health.

How long do pet rats live?

The maximum lifespan is about three years. Wild rats mostly live only about a year, mainly because of predators and conflict.

Are pet rats the same as wild rats?

Fancy rats are a domesticated subspecies of the brown rat, produced by selective breeding. Domesticated rats show much less fear of new things than wild ones.

Do rats sleep during the day?

Rats are nocturnal, so they are mostly active at night. Albino strains of laboratory rats have been found to be less active during the day than pigmented ones.

What does it mean when my rat grinds its teeth?

This is called bruxing, and it is most usually triggered by happiness. It can also be self-comforting in stressful situations, such as a vet visit.

Do rats really laugh?

When tickled or playing, rats make a high-pitched chirping that has been likened to laughter. It is too high for humans to hear without special equipment.

Do rats spread the plague?

Brown rats are sometimes mistakenly thought to be a major source of bubonic plague. The bacterium is usually carried by fleas and is common in only a few rodent species.

Stories of rats growing as big as cats are exaggerations or misidentifications of larger rodents. The heaviest live brown rat on record weighed 822 g.

Rats see some ultraviolet light that humans cannot, though they see colours rather like a person with red-green colour blindness.

The common idea that cities hold as many rats as people is considered an urban myth for most cities.

In the Canadian province of Alberta, keeping unlicensed rats, including fancy rats, is against the law for most people.

A 2007 study suggested rats might have metacognition, though later analysis suggested simpler learning could explain the result.