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- This is an article about wild rats. For pet rats, see Fancy rat. For other uses, see Rat (disambiguation).
Black Rat (Rattus rattus)
50 species; see text
Rats are various medium sized rodents. "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, R. norvegicus. Many members of other rodent genera and families are also called rats and share many characteristics with true rats.
Rats are distinguished from mice by their size; rats generally have bodies longer than 12 cm (5 inches). Squirrels of most species are about the same size as rats but are members of their own family, Sciuridae, and are usually more specialized than rats.
The best-known rat species are the Black Rat Rattus rattus and the Brown Rat R. norvegicus. The group is generally known as the Old World rats or true rats, and originated in Asia. Rats are bigger than most of their relatives, the Old World mice, but seldom weigh over 500 grams (1 lb) in the wild. The common 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 a number of others. Other rats such as the Bandicoot rat Bandicota bengalensis are murine rodents related to the true rats, but are not members of the genus Rattus. The widely distributed and problematic commensal species of rats represent 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 brown, black, or Polynesian rats.
In Western countries, many people keep domesticated rats as pets. These are of the species R. norvegicus, which originated in the grasslands of China and spread to Europe and eventually, in 1775, to the New World. Pet rats are Brown Rats descended from those bred for research, and are often called "fancy rats", but they are still the same species as the common city "sewer" rat. Domesticated rats tend to be both more docile than their wild ancestors and more disease prone, presumably due to inbreeding.
The common species are opportunistic survivors and often live with and near humans. The Black Plague is traditionally believed to have been caused by the micro-organism Yersinia pestis, carried by the rat flea Xenopsylla cheopis which preyed on R. rattus living in European cities of the day; it is notable that these rats were victims of the plague themselves. It has recently been suggested that neither rats nor infected fleas would have spread fast enough through Europe to be a likely culprit, although this is controversial and research continues. Regardless, rats are frequently blamed for damaging food supplies and other goods. Their reputation has carried into common parlance: in the English language, "rat" is an insult and "to rat on someone" is to betray them by denouncing to the authorities a crime or misdeed they committed. While modern wild rats can carry Leptospirosis and some other "zoonotic" conditions (those which can be transferred across species, to humans, for example), these conditions are in fact rarely found. Wild rats living in good environments are typically healthy and robust animals. Wild rats living in cities may suffer themselves from poor diet and internal parasites and mites, but do not generally spread disease to humans.
Rats have a normal lifespan ranging from two to five years, though three years is typical.
Rats as vermin
By most standards, rats are considered pests or vermin. They can be very destructive to crops and property. Rats can quickly overpopulate when they live in a place where they have no predators, such as in certain cities, and their numbers can become hard to contain. Because of this, the entire province of Alberta, Canada has upheld and maintained a rat-free status since the early 1950s; it is even illegal to keep pet rats there.
Rats have a significant impact on food production. Estimates vary, but it is likely that about one-fifth of the world's total food output is eaten, spoiled or destroyed by rats.  It is interesting to note that about one-third of the food purchased by humans is thrown away as garbage in certain areas. 
Rats can carry over thirty different diseases dangerous to humans, including Weil's disease, typhus, salmonella and bubonic plague. Black rats are suspected to have had a role in the Black Death, an epidemic which killed at least 75 million people in Europe, the Middle East, and Asia in the mid-late 14th century.
A variety of rat control methods have been used throughout human history to either reduce or eliminate rat populations in homes, markets, farms, and industrial sites. The two most widely used methods are rat poison and rat traps, though cats and dogs have also been employed to hunt rats. Professional rat-catchers can be found in many developing countries.
Because rats are nocturnal, daytime sightings of rat activity can mean that their nesting areas have been disturbed or, more likely, that there is overpopulation of them in the local area.  It is typically at this point that vermin control measures tend to increase.
Rats often chew electrical cables. Around 26% of all electrical cable breaks are caused by rats, and around 18% of all phone cable breaks. Around 25% of all fires of unknown origin are estimated to be caused by rats.
Rats, particularly roof rats (Rattus rattus), can enter the attics of homes where they mate and nest. This problem occurs commonly in coastal, temperate climates and affects even the cleanest, well-kept homes.
Rats as pets
Specially bred rats have been kept as pets at least since the late 19th century. Rats are intelligent animals and can be trained to use a litter box, come when called, and perform a variety of tricks. Pet rats are typically of variants of the species R. Norvegicus, or Brown rat, but Black rats and Giant pouched rats are also known to be kept. Pet rats behave differently than their wild relatives depending on how many generations they have been removed, and when acquired from reliable sources, they do not pose any more health risk than other, more common pets.
Rats as subjects of scientific research
In 1895, Clark University in Worcester, Massachusetts (United States) established a population of domestic white 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 wellbeing of humankind. Laboratory rats have also proved valuable in psychological studies of learning and other mental processes (Barnett 2002). A 2007 study found rats to possess metacognition, a mental ability previously only found in humans and some primates.
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 model organisms for scientific research. When conducting genetic research rats are much rarer than mice. When it comes to conducting tests related to intelligence, learning and drug abuse rats are a popular choice since 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 like the Wistar rat have been bred for use in laboratories. Much of the genome of Rattus norvegicus has been sequenced.
Laughter in rats
It was discovered that rats emit short, high frequency, ultrasonic, socially induced vocalization during rough and tumble play, and when tickled. The vocalization is described as a distinct “chirping”. Humans cannot hear the “chirping” without special equipment. It was also discovered that like humans, rats have “tickle skin”. These are certain areas of the body which generate more laughter response than other areas. The laughter is associated with positive emotional feelings and social bonding occurs with the human tickler, resulting in the rats becoming conditioned to seek the tickling. Additional responses to the tickling were those that laughed the most also played the most, and those that laughed the most preferred to spend more time with other laughing rats. This suggests a social preference to other rats exhibiting similar responses. However, as the rats age, there does appear to be a decline in the tendency to laugh and respond to tickle skin. The initial goal of Jaak Panksepp & Jeff Burgdorf’s research was to track the biological origins of joyful and social processes of the brain by comparing rats and their relationship to the joy and laughter commonly experienced by children in social play. Although, the research was unable to prove rats have a sense of humor, it did indicate rats can laugh and express joy. Panksepp & Burgdorf 2003 Chirping by rats is also reported in additional studies by Brian Knutson of the National Institutes of Health. Rats chirp when wrestling one another, before receiving morphine, or having sex. The sound has been interpreted as an expectation of something rewarding. Science News 2001
Rats as food
Rats, like all mammals, are edible by humans and are sometimes captured and eaten in emergency situations. Bandicoot rats are an important food source among some peoples in India and Southeast Asia. Among the reasons rat meat is not more widely utilized are the strong prohibitions against it in Islamic and Jewish dietary laws, the prohibition of all meat in Hinduism, and the rat's bad reputation in many cultures.
Rats in culture
Ancient Romans did not generally differentiate between rats and mice, instead referring to the former as Mus Maximus (big mouse) and the latter as Mus Minimus (little mouse).
In Imperial Chinese culture, the rat (sometimes referred to as a mouse) is the first of the twelve animals of the Chinese zodiac. People born in this year are expected to possess qualities associated with rats. These include creativity, honesty, generosity, ambition, a quick temper and wastefulness. "Rats" (i.e. people born in a year of the rat) are said to get along well with "monkeys" and "dragons," and to get along poorly with "horses."
In India in the northwestern city of Deshnoke, the Karni Mata Temple, the rats are held to be destined for reincarnation as Sadhus, Hindu holy men. The attending priests feed milk and grain, of which the pilgrims also partake, to the animals. Eating food that has been touched by the animals is considered a blessing from god.
Western associations with the rat are generally negative. For instance, "Rats!" is used as a substitute for various vulgar interjections. These associations do not draw, per se, from any biological or behavioral trait of the rat, but possibly from the association of rats (and fleas) with the 14th-century medieval plague called the Black Death. Rats are seen as vicious, unclean, parasitic animals that steal food and spread disease. However many people in Western cultures keep rats as pets and conversely find them to be tame, clean, intelligent, and playful. While undomesticated rats, dogs, and cats may all be pests in urban areas, in Western countries poisoning rats is commonly accepted, while doing the same to feral dogs and cats would be an unpopular solution in the view of many people.
Describing a person as "rat-like" usually implies he is unattractive and suspicious. In contrast, mice are stereotyped as cute and bourgeois.
Rats are often used in scientific experiments; many animal rights activists allege that treatment of rats in this context is cruel. The term "lab rat" is therefore sometimes used, like guinea pig, to describe a person who is manipulated in a social experiment.
Rats in pop culture
- Mutant, man-eating rats are the monsters in James Herbert's horror novel The Rats and its sequels.
- A phobia of rats is used as a torture device in the novel Nineteen Eighty-Four by George Orwell.
- Rats are the most common enemy in Brian Jacques's Redwall series of anthropomorphic fantasy novels.
- There are obvious exceptions; for example, the characters of Mrs. Frisby and the Rats of NIMH, the television series Ratz, Rizzo the Rat from The Muppets and Terry Pratchett's The Amazing Maurice and his Educated Rodents.
- Rats also appear in numerous video and computer games as killable monsters. In many of these games, rats appear much larger than normal.
- Splinter of Teenage Mutant Ninja Turtles fame is a mutated rat.
- Templeton of E.B. White's children's book, Charlotte's Web, is a Brown rat, devoid of morals, that lives on the farm, underneath Wilbur's food trough.
- A media frenzy developed in New York City 23 Feb. 2007, when a dozen rats invaded a Taco Bell, and ran unimpeded.
- A Transformers character called Rattrap can transform into a rat.
- Malevolent rats in H. P. Lovecraft's short story "The Rats in the Walls"
- Disney's upcoming Pixar release, Ratatouille, features a rat named Rémy seeking to become a fine chef.
- In the 1971 film Willard and the 2003 remake Willard (2003 film).
- In Peanuts, Charlie Brown's favorite utterance, catch phrase is 'Rats!', shouted after suffering yet another personal reversal.
- Spike TV aired Gary The Rat, an animated series revolving around a debauched attorney named Gary Andrews who mysteriously transforms into an anthropomorphic gray rat.
Taxonomy of Rattus
The genus Rattus is a member of the giant subfamily Murinae. There are several other murine genera that are sometimes considered part of Rattus. : Lenothrix, Anonymomys, Sundamys, Kadarsanomys, Diplothrix, Margaretamys, Lenomys, Komodomys, Palawanomys, Bunomys, Nesoromys, Stenomys, Taeromys, Paruromys, Abditomys, Tryphomys, Limnomys, Tarsomys, Bullimus, Apomys, Millardia, Srilankamys, Niviventer, Maxomys, Leopoldamys, Berylmys, Mastomys, Myomys, Praomys, Hylomyscus, Heimyscus, Stochomys, Dephomys, and Aethomys.
The genus Rattus proper contains 56 species. A subgeneric breakdown of the species has been proposed, but does not include all species. The five groups are:
- norvegicus group
- rattus group
- Australian native rat species
- New Guinea native rat species
- xanthurus group
The following list is alphabetical.
Species of rats
- Genus Rattus
- Rattus adustus
- Rattus annandalei
- Rattus argentiventer
- Rattus baluensis
- Rattus bontanus
- Rattus burrus
- Rattus colletti
- Rattus elaphinus
- Rattus enganus
- Rattus everetti
- Rattus exulans
- Rattus feliceus
- Rattus foramineus
- Rattus fuscipes
- Rattus giluwensis
- Rattus hainaldi
- Rattus hoffmani
- Rattus hoogerwerfi
- Rattus jobiensis
- Rattus koopmani
- Rattus korinchi
- Rattus leucopus
- Rattus losea
- Rattus lugens
- Rattus lutreolus
- Rattus macleari
- Rattus marmosurus
- Rattus mindorensis
- Rattus mollicomulus
- Rattus montanus
- Rattus mordax
- Rattus morotaiensis
- Rattus nativitatis
- Rattus nitidus
- Rattus norvegicus
- Rattus novaeguineae
- Rattus osgoodi
- Rattus palmarum
- Rattus pelurus
- Rattus praetor
- Rattus ranjiniae
- Rattus rattus
- Rattus sanila
- Rattus sikkimensis
- Rattus simalurensis
- Rattus sordidus
- Rattus steini
- Rattus stoicus
- Rattus tanezumi
- Rattus tawitawiensis
- Rattus timorensis
- Rattus tiomanicus
- Rattus tunneyi
- Rattus turkestanicus
- Rattus villosissimus
- Rattus xanthurus
- The Story of Rats: Their Impact on Us, and Our Impact on Them, S. Anthony Barnett, Allen & Unwin, Crows Nest, NSW, Australia, 2002, trade paperback, 202 pages, ISBN 1-86508-519-7 .
- Jahn, G. C., P. Cox, S. Mak, and N. Chhorn 1999. Farmer participatory research on rat management in Cambodia. In G. Singleton, L. Hinds, H. Leirs and Zhibin Zhang [Eds.] “Ecologically-based rodent management” ACIAR, Canberra. Ch. 17, pp. 358-371. ISBN: 1 86320 262 5
- Leung LKP, Peter G. Cox, G. C. Jahn and Robert Nugent. 2002. Evaluating rodent management with Cambodian rice farmers. Cambodian Journal of Agriculture Vol. 5, pp. 21-26.
- Matthews, I. (1898) 1st ed. Full Revelations of a Professional Rat-Catcher, after 25 Years’ Experience. Manchester: Friendly Societies Printing Co. ISBN 1-905124-64-3
- Musser, G. G. and M. D. Carleton. 1993. Family Muridae. Pp. 501-755 in Mammal Species of the World a Taxonomic and Geographic Reference. D. E. Wilson and D. M. Reeder eds. Smithsonian Institution Press, Washington D.C.
- Nowak, R. M. 1999. Walker's Mammals of the World, Vol. 2. Johns Hopkins University Press, London.
- Sullivan, Robert. 2004. Rats - A Year with New York´s Most Unwanted Inhabitants. Granta Books, London.
- Sullivan, Robert. 2005. Rats: Observations on the History and Habitat of the City's Most Unwanted Inhabitants. Bloomsbury USA. ISBN 1-58234-477-9
References and notes
- ^ | Rats Capable Of Reflecting On Mental Processes
- ^ Genome project. www.ensemble.org. Retrieved on February 17, 2007.
- ^ Hollywood Rats