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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.

Contents [hide]
1 Species and description
2 As pets
3 As subjects for scientific research
3.1 General intelligence
3.2 Social intelligence
4 As food
5 Working rats
6 For odor detection
7 In the spread of disease
8 As pests
9 As invasive species
10 Rat-free areas
11 Taxonomy of Rattus
11.1 Species
12 In culture
12.1 Asian cultures
12.2 European cultures
12.2.1 Terminology
12.3 Fiction
12.3.1 The Pied Piper
13 See also
14 References
15 Further reading
16 External links
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.[1]

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 referred to as a mischief.[2]

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.[3] 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.[4]

Wild rodents, including rats, can carry many different zoonotic pathogens, such as Leptospira, Toxoplasma gondii, and Campylobacter.[5] 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. Another zoonotic disease linked to the rat is the foot-and-mouth disease.[6]


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.[7]

The black and brown rats diverged from other Old World rats during the beginning of the Pleistocene in the forests of Asia.[8]

As pets

Main 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.[9] Pet rats do not pose any more of a health risk than pets such as cats or dogs.[10] Tamed rats are generally friendly and can be taught to perform selected behaviors.

As subjects for scientific research

Main article: Laboratory rat

A laboratory rat strain, known as a Zucker rat, bred to be genetically prone to diabetes, a metabolic disorder also 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.[11][12]

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,[13] 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, and adaptability. 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.[14]

General intelligence
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Because of evident displays of their ability to learn,[15] 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.[16][17] Quoting Galsworthy, with regard to the affirmative 1935 Thorndike work:[18]

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...[18]

However, some more contemporary work has not supported the earlier affirmative view.[19] 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 ev

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