Rats are various medium-sized, long-tailed rodents of the superfamily Muroidea. "True rats" are

members of the genus Rattus, the most important of which to humans are the black rat, Rattus

rattus, and the brown rat, Rattus norvegicus. Many members of other rodent genera and families are

also referred to as rats, and share many characteristics with true rats.

Rats are typically distinguished from mice by their size. Generally, when someone discovers a

large muroid rodent, its common name includes the term rat, while if it is smaller, the name includes

the term mouse. The muroid family is broad and complex, and the common terms rat and mouse are

not taxonomically specific. Scientifically, the terms are not confined to members of

the Rattus and Mus genera, for example, the pack rat and cotton mouse.

Species and description

A river rat

A rat in a city street

The best-known rat species are the black rat (Rattus rattus) and the brown rat (Rattus norvegicus).

The group is generally known as the Old World rats or true rats, and originated in Asia. Rats are

bigger than most Old World mice, which are their relatives, but seldom weigh over 500 grams

(1.1 lb) in the wild.[citation needed]

The term "rat" is also used in the names of other small mammals which are not true rats. Examples

include the North American pack rats, a number of species loosely called kangaroo rats, and others.

Rats such as the bandicoot rat (Bandicota bengalensis) are murine rodents related to true rats, but

are not members of the genus Rattus. Male rats are called bucks, unmated females are called does,

pregnant or parent females are called dams, and infants are called kittens or pups. A group of rats is

either referred to as a pack or a mischief.[citation needed]

The common species are opportunistic survivors and often live with and near humans; therefore,

they are known as commensals. They may cause substantial food losses, especially in developing

countries.[1] However, the widely distributed and problematic commensal species of rats are a

minority in this diverse genus. Many species of rats are island endemics and some have become

endangered due to habitat loss or competition with the brown, black or Polynesian rat.[citation needed]

Wild rodents, including rats, can carry many different zoonotic pathogens, such

as Leptospira, Toxoplasma gondii, and Campylobacter.[2] The Black Death is traditionally believed to

have been caused by the micro-organism Yersinia pestis, carried by the tropical rat flea (Xenopsylla

cheopis) which preyed on black rats living in European cities during the epidemic outbreaks of the

Middle Ages; these rats were used as transport hosts. Other zoonotic diseases linked to pest

rodents include classical swine fever and foot-and-mouth disease.[citation needed]

A rat in a suburb of Vancouver

The average lifespan of any given rat depends on which species is being discussed, but many only

live about a year due to predation.[citation needed]

The black and brown rats diverged from other Old World rats during the beginning of

the Pleistocene in the forests of Asia.[citation needed]

PetsMain article: Fancy rat

A domesticated rat

Specially bred rats have been kept as pets at least since the late 19th century. Pet rats are typically

variants of the species brown rat, but black rats and giant pouched rats are also known to be kept.

Pet rats behave differently from their wild counterparts depending on how many generations they

have been kept as pets.[3] Pet rats do not pose any more of a health risk than pets such

as cats or dogs.[4] Tamed rats are generally friendly and can be taught to perform selected behaviors.

Subjects for scientific researchMain article: Laboratory rat

A laboratory rat strain, known as a Zucker rat, is bred to be genetically prone to diabetes, the same metabolic

disorder found among humans.

In 1895, Clark University in Worcester, Massachusetts (United States) established a population of

domestic albino brown rats to study the effects of diet and for other physiological studies. Over the

years, rats have been used in many experimental studies, which have added to our understanding

of genetics, diseases, the effects of drugs, and other topics that have provided a great benefit for

the health and well-being of humankind. Laboratory rats have also proved valuable in psychological

studies of learning and other mental processes (Barnett, 2002), as well as to understand group

behavior and overcrowding (with the work of John B. Calhoun on behavioral sink). A 2007 study

found rats to possess metacognition, a mental ability previously only documented in humans and

some primates.[5][6]

Domestic rats differ from wild rats in many ways. They are calmer and less likely to bite; they can

tolerate greater crowding; they breed earlier and produce more offspring; and

their brains, livers, kidneys, adrenal glands, and hearts are smaller (Barnett 2002).

Brown rats are often used as model organisms for scientific research. Since the publication of the rat

genome sequence,[7] and other advances, such as the creation of a rat SNP chip, and the production

of knockout rats, the laboratory rat has become a useful genetic tool, although not as popular

as mice. When it comes to conducting tests related to intelligence, learning, and drug abuse, rats are

a popular choice due to their high intelligence, ingenuity, aggressiveness, andadaptability.

Their psychology, in many ways, seems to be similar to humans. Entirely new breeds or "lines" of

brown rats, such as the Wistar rat, have been bred for use in laboratories. Much of the genome

of Rattus norvegicus has been sequenced.[8]

General intelligence[improper synthesis?]

This section needs additional citations for verification. Please

help improve this article by adding citations to reliable sources.

Unsourced material may be challenged and removed. (January 2015)

Because of evident displays of their ability to learn,[citation needed] rats were investigated early to see

whether they exhibit general intelligence, as expressed by the definition of a g factor and observed in

larger, more complex animals.[citation needed] Early studies ca. 1930 found evidence both for and against

such a g factor in rat.[9][10] Quoting Galsworthy, with regard to the affirmative 1935 Thorndike work:[11]

Robert Thorndike, for example, provided strong evidence for g in rats by the use of a variety of tests

such as mazes, problem-solving tasks, and simple avoidance conditioning... Performances tended to

correlate across tasks, with stronger associations found between mazes and problem-solving than

with simple avoidance tasks. Thorndike... also reviewed a dozen earlier studies which also

suggested that the highest correlations are found between more complex problem-solving tasks.

However, it should be noted that there were other contemporary studies that found split or near zero-

order correlation matrices for other populations of rats across cognitive batteries...[11]

However, some more contemporary work has not supported the earlier affirmative view.

[12] Throughout the 1990s and into the 2000s, series of articles have appeared attempting to address

the question of general intelligence in this species, through measurements of tasks performed by

rats and mice, e.g., with statistical evaluation by factor analysis, and seeking to correlate general

intelligence and brain size (as is done with humans and primates),[medical citation needed][13][full citation needed] where the

general conclusion was in the affirmative.[need quotation to verify][improper synthesis?][citation needed]

Social intelligence[improper synthesis?]

A 2011 controlled study found that rats are actively prosocial.[citation needed] They demonstrate apparent

altruistic behaviour to other rats in experiments, including freeing them from cages: when presented

with readily available chocolate chips, test subjects would first free the caged rat, and then share the

food. All female rats in the study displayed this behaviour, while 30% of the males did not. [14]

Food

Rat meat dishes in Yangshuo,Guangxi, China

Rat meat is a food that, while taboo [15] [16]  in some cultures, is a dietary staple in others. Taboos

include fears of disease or religious prohibition, but in many places, the high number of rats has led

to their incorporation into the local diets.

In some cultures, rats are or have been limited as an acceptable form of food to a particular social or

economic class. In the Mishmi culture of India, rats are essential to the traditional diet, as Mishmi

women may eat no meat except fish, pork, wild birds and rats.[17] Conversely,

the Musahar community in north India has commercialised rat farming as an exotic delicacy.[18] In the

traditional cultures of the Hawaiians and the Polynesians, rat was an everyday food for commoners.

When feasting, the Polynesian people of Rapa Nui could eat rat meat, but the king was not allowed

to, due to the islanders' belief in his "state of sacredness" called tapu.[19] In studying precontact

archaeological sites in Hawaii, archaeologists have found the concentration of the remains of rats

associated with commoner households accounted for three times the animal remains associated

with elite households. The rat bones found in all sites are fragmented, burned and covered in

carbonized material, indicating the rats were eaten as food. The greater occurrence of rat remains

associated with commoner households may indicate the elites of precontact Hawaii did not consume

them as a matter of status or taste.[20]

Bandicoot rats are an important food source among some peoples in Southeast Asia, and the United

Nations Food and Agriculture Organization estimated rat meat makes up half the locally produced

meat consumed in Ghana, where cane rats are farmed and hunted for their meat. African slaves in

the American South were known to hunt wood rats (among other animals) to supplement their food

rations,[21] and Aborigines along the coast in southern Queensland, Australia, regularly included rats

in their diet.[22]

Ricefield rats (Rattus argentiventer) have traditionally been used as food in rice-producing regions

such as Valencia, as immortalized by Vicente Blasco Ibáñez in his novel Cañas y barro. Along

with eeland local beans known as garrafons, rata de marjal (marsh rat) is one of the main

ingredients in traditional paella (later replaced by rabbit, chicken and seafood).[23] Ricefield rats are

also consumed in the Philippines, the Isaan region of Thailand, and Cambodia. In late 2008, Reuters

reported the price of rat meat had quadrupled in Cambodia, creating a hardship for the poor who

could no longer afford it.

Elsewhere in the world, rat meat is considered diseased and unclean, socially unacceptable, or there

are strong religious proscriptions against it. Islam and Kashrut traditions prohibit it, while both

theShipibo people of Peru and Sirionó people of Bolivia have cultural taboos against the eating of

rats.[24][25]

Rats are a common food item for snakes, both in the wild, and as pets. Captive-bred ball pythons, in

particular, are fed a diet of mostly rats. Rats are available to individual snake owners, as well as to

large reptile zoos, from many suppliers. In Britain, the government in 2007 ruled out the feeding of

any live mammal to another animal. The rule says the animal must be dead (frozen) then given to

the animal to eat. The rule was put into place mainly because of the pressure of the RSPCA and

people who found it cruel.

Medicine

Rats can serve as zoonotic vectors for certain pathogens and thus cause disease, such as Lassa

fever, leptospirosis and Hantavirus infection.[citation needed]

Odor detection

Rats have a keen sense of smell and are easy to train. These characteristics have been employed,

for example, by the Belgian non-governmental organization APOPO, which trains rats

(specificallyAfrican giant pouched rats) to detect landmines and diagnose tuberculosis through smell.

[26]

Rats as pests

Rats have long been considered deadly pests. Once considered a modern myth, the rat

flood in India has now been verified. Indeed every fifty years, armies of bamboo rats descend upon

rural areas and devour everything in their path.[27] Rats have long been held up as the chief villain in

the spread of the Bubonic Plague,[28] however recent studies show that they alone could not account

for the rapid spread of the disease through Europe in the Middle Ages.[29] Still, the Center for Disease

Control does list nearly a dozen diseases [30] directly linked to rats. Most urban areas battle rat

infestations.Rats in New York City are famous for their size and prevalence. The urban legend that

the rat population in Manhattan equals that of its human population (a myth definitively refuted by

Robert Sullivan in his book "Rats") speaks volumes about New Yorkers' awareness of the presence,

and on occasion boldness and cleverness, of the rodents.[31] New York has specific regulations for

getting rid of rats—multi-family residences and commercial businesses must use a specially trained

and licensed exterminator.[32] Places to look for rat infestations are around pipes, behind walls and

near garbage cans. Effective rat control requires municipal workers and individuals to work together.

[citation needed]

Rats as invasive species

When introduced into locations where rats previously did not exist they can cause a huge amount

of environmental degradation. Rattus rattus, the black rat, is considered to be one of the world's

worst invasive species.[33] Also known as the ship rat, it has been carried world-wide as

a stowaway on sea-going vessels for millennia and has usually accompanied men to any new area

visited or settled by human beings by sea. The similar but more aggressive species Rattus

norvegicus, the brown rat or wharf rat, has also been carried world wide by ships in recent

centuries.

The ship or wharf rat has contributed to the extinction of many species of wildlife including birds,

small mammals, reptiles, invertebrates, and plants, especially on islands. True rats are omnivorous

and capable of eating a wide range of plant and animal foods. True rats have a very high birth rate.

When introduced to a new area, they quickly reproduce to take advantage of the new food supply. In

particular, they prey on the eggs and young of forest birds, which on isolated islands often have no

other predators and thus have no fear of predators.[34] Some experts believe that rats are to blame for

between 40 percent and 60 percent of all seabird and reptile extinctions, with 90 percent of those

occurring on islands. Thus man has indirectly caused the extinction of many species by accidentally

introducing rats to new areas.[35]

Rat-free areas

The only rat-free continent is Antarctica, due to its hostile climate which is too severe for rat survival,

and its lack of human habitation to provide buildings to shelter them from the weather. However, rats

have been introduced to many of the islands near Antarctica, and because of their destructive effect

on native flora and fauna, efforts to eliminate them are on-going. In particular, Bird Island (just off rat-

infested South Georgia), where breeding seabirds could be badly affected if rats were introduced, is

subject to special measures and regularly monitored for rat invasions.[36]

As part of island restoration some islands' rat populations have been eradicated to protect or restore

the ecology. Hawadax Island, Alaska was declared rat free after 229 years and Campbell Island,

New Zealand after almost 200 years. Breaksea Island in New Zealand was declared rat free in 1988

after an eradication campaign based on a successful trial on the smaller Hawea Island nearby.

In January, 2015 an international "Rat Team" set sail from the Falkland Islands for the British

Overseas Territory of South Georgia on board a ship carrying three helicopters and 100 tons of rat

poison with the objective of "reclaiming the island for its seabirds". Rats have wiped out more than

90% of the seabirds on South Georgia, and the sponsors hope that once the rats are gone, it will

regain its former status as home to the greatest concentration of seabirds in the world. The South

Georgia Heritage Trust, which organized the mission describes it as "five times larger than any other

rodent eradication attempted worldwide". [37] That would be true if it were not for the rat control

program in Alberta (see below).

The Canadian province of Alberta (population 4.1 million) is notable for being the largest inhabited

area on Earth (bigger than any country in the European Union including France) which is free of true

rats. It has large numbers of pack rats, also called bushy-tailed wood rats, but they are native

species which are much less destructive than true rats. They are forest-dwelling vegetarians, and

their worst trait is that because of their attraction for shiny objects, they tend to sneak into cabins and

hotels and steal jewelry, silverware, and other valuable items.[38]

Alberta is one of only two Canadian provinces with no sea access, and was settled relatively late in

North American history. The black rat cannot survive in its climate at all, and brown rats must live

near people and their structures. They cannot evade the numerous predators in natural areas or

survive the winters in farm fields. It took until 1950 for invading rats to make their way to Alberta over

land from Eastern Canada.[39] Immediately upon their arrival at the eastern border

with Saskatchewan, the Alberta government implemented an extremely aggressive rat control

program to stop them from advancing further. A systematic detection and eradication system was

used throughout a control zone about 600 kilometres (400 mi) long and 30 kilometres (20 mi) wide

along the eastern border of the province to eliminate rat infestations before the rats could spread

further into the province. Shotguns, bulldozers, high explosives, poison gas, and incendiaries were

used to destroy rats. Numerous farm buildings were destroyed in the process. Initially, tons

of arsenic trioxide were spread around thousands of farm yards to poison rats, but soon after the

program commenced the rodenticide and medical drug warfarin was introduced, which is much safer

for people (it is a commonly prescribed medicine), and more effective at killing rats than arsenic. [40]

Forceful government control measures, strong public support and enthusiastic citizen participation

continue to keep rat infestations to a minimum.[41] The effectiveness has been aided by a similar but

newer program in Saskatchewan which prevents rats from even reaching the Alberta border. The

program still actively employs an armed rat patrol (in this case, not just a TV show) along Alberta's

borders, about ten single rats are found and killed per year, and occasionally a large localized

infestation has to be dug out with heavy machinery, but the number of rat infestations (two or more

rats) found in most recent years has averaged about three, and in many years has been zero.