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 called rats and share many characteristics with true rats.
Rats are typically distinguished from mice by their size; rats are generally large muroid rodents, while mice are generally small muroid rodents. The muroid family is very large and complex, and the common terms rat and mouse are not taxonomically specific. Generally, when someone discovers a large muroid, its common name includes the term rat , while if it is small, the name includes the term mouse - scientifically, the terms are not confined to members of the Rattus and Mus genera. Compare the taxonomic classification of the Pack rat and Cotton mouse.
Species and description
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 lb) in the wild.
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 .
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 are 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, therefore they are known as commensals. They may cause substantial food losses, especially in developing countries. 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.
Wild rats can carry many different "zoonotic" pathogens, such as e.g. Leptospira, Toxoplasma gondii and Campylobacter, and may transfer these across species, for example to humans. 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 Rat living in European cities during the epidemic outbreaks of the Middle Ages; these rats were used as transport hosts. Today, this cycle still exists in many countries of the world and plague outbreaks still occur every year. Beside transmitting zoonotic pathogens, rats are also linked to the spread of contagious animal pathogens that may result in livestock diseases such as Classical Swine Fever and Foot-and-mouth disease.
The normal lifespan of rats ranges from two to five years, and is typically three years.
As pets
Main article: Fancy ratSpecially 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 than their wild counterparts depending on how many generations they have been kept as pets. Pet rats do not pose any more of a health risk than pets such as cats and dogs. Tamed rats are generally friendly and can be taught to perform selected behaviors.
As subjects of scientific research
Main article: Laboratory ratIn 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), 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.
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 , 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 like the Wistar rat have been bred for use in laboratories. Much of the genome of Rattus norvegicus has been sequenced.
As food
Rats are edible by humans and are sometimes captured and eaten in emergency situations. For some cultures, rats are considered a staple. Bandicoot rats are an important food source among some peoples in Southeast Asia. Reasons why rat meat is not more widely eaten include the strong proscription against it in Halal and Kashrut tradition, and the fact that eating rat is not socially accepted in many cultures.
Another argument against eating rat is the risk of Weil's disease: the British SAS's rule book lists rat as the only meat which its members in action are not allowed to eat.
As a food, rats are often a more-readily available source of protein than other fauna. Some African slaves in the American South hunted wood rats (among other animals) to supplement their food rations. The Aborigines along the coast in Southern Queensland, Australia regularly included rats in their diet. In the Mishmi culture of India, rats are essential to the Mishmi traditional diet, as Mishmi women may eat no meat except fish, pork, wild birds and rats. The United Nations Food and Agriculture Organization estimates that rat meat makes up half the locally produced meat consumed in Ghana, where cane rats are farmed and hunted for their meat.
Ricefield rats have been traditionally used as food in rice-producing regions, like in Valencia, where along with the eel and local beans known as "garrafons" the rata de marjal was one of the main ingredients of the original paella (later replaced by rabbit, chicken and seafood). The rat-eating habits of the people of the rice growing region of Valencia were immortalized by Vicente Blasco Ibáñez in his novel Cañas y barro .
Ricefield rats (Rattus argentiventer) are also consumed in the Philippines and the Isaan region of Thailand, as well as Cambodia, particularly when meat prices have been inflated. In late 2008, Reuters reported that the price of rat meat had quadrupled in Cambodia creating a hardship for the poor who could no longer afford it. Cambodia also exports about a metric ton of rats daily to Vietnam as food.
In some cultures, rats are or have been limited as an acceptable form of food to a particular social or economic class. The Musahar community in north India commercialised rat farming as a exotic delicacy. In the traditional cultures of the Hawaiians and the Polynesians, rat was a common food. When feasting, the Polynesian people of Rapa Nui could eat rat, but the king was not allowed to due to the islanders' belief in a "state of sacredness" called tapu . In studying pre-contact archaeological sites in Hawaii, archaeologists have found that the concentration of the remains of rats associated with commoner households counted 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 that rats were eaten as food. The greater occurrence of rat remains associated with commoner households may indicate that the elites of pre-contact Hawaii did not consume them as a matter of status or taste.
The taboo against consuming rats as food is not unique to the world's major religions or Western cultures. Both the Shipibo people of Peru and Sirionó people of Bolivia have cultu
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