The brown rat is the larger of the two, growing up to 10 in. (25 cm) long excluding the naked, scaley tail and sometimes weighing more than a pound (.5 kg). It is commonly brown with whitish underparts and pink ears, feet, and tail. It is a poor climber, but an excellent burrower and swimmer; it is found in the damp basements and sewers of most temperate zone cities. The laboratory white rat is an albino strain of the brown rat.
The black rat is commonly dark gray. It reaches a maximum length of 8 in. (20 cm) and has a longer tail and larger ears than the brown rat. A good climber, the black rat inhabits attics and upper floors in warm areas; it is the common rat of the Mediterranean region, the SE United States, and Central and South America.
Rats are omnivorous, aggressive, intelligent, adaptable, and extremely fecund. Females produce as many as 8 litters each year with as many as 20 young per litter. The gestation period is three weeks, and the young reach sexual maturity in about two months. Rats may live as long as four years. They are social animals but sometimes fight among themselves.
Rats live mostly in and around human settlements, where they have few natural enemies and an abundant source of food. They invade food supplies and cause widespread destruction; they also spread human diseases such as typhus and tularemia. Despite human efforts to exterminate rats, the house rat population is probably equal to the human population.
Besides the house rats, the genus Rattus contains several hundred wild-living species. In addition, many other members of several different rodent families are called rats, e.g., the bandicoot rat, the wood rat, or pack rat, the rice rat, the muskrat, and the kangaroo rat. House rats are classified in the phylum Chordata, subphylum Vertebrata, class Mammalia, order Rodentia, family Muridae.
See also mouse.
See H. Zinsser, Rats, Lice and History (1935); S. A. Barnett, The Rat, a Study in Behavior (1963).
Rats are distinguished from mice by their size; rats generally have bodies longer than .
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. 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.
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. The Black Plague is traditionally believed to have been caused by the micro-organism Yersinia pestis, carried by the Tropical Rat Flea (Xenopsylla cheopis) which preyed on R. rattus living in European cities of the day; these rats were victims of the plague themselves.
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 (not true in neotropical countries). Wild rats living in good environments are typically healthy and robust animals. Wild rats living in cities may suffer from poor diets and internal parasites and mites, but do not generally spread disease to humans.
The normal lifespan of rats ranges from two to five years, and is typically three years.
Specially bred rats have been kept as pets at least since the late 19th century. Pet rats are typically of 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.
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 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. 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 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 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.
Rats have been used as food by the poor in 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 Viet Nam 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 cultural taboos against the eating of rats.
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, as food items, are available from many suppliers who supply to individual snake owners as well as to large reptile zoos.
In Indian tradition rats are recognized as the vehicle of Lord Ganesh and a rat's statue is always found in a temple of Ganesh. In the northwestern Indian city of Deshnoke, the rats at the Karni Mata Temple are held to be destined for reincarnation as Sadhus (Hindu holy men). The attending priests feed milk and grain to the rats, of which the pilgrims also partake. Eating food that has been touched by rats is considered a blessing from god.
Rats are often used in scientific experiments; animal rights activists allege that treatment of rats in this context is cruel. The term "lab rat" is used, typically in a self-effacing manner, to describe a person whose job function requires that they spend a majority of their work time engaged in bench-level research (i.e. a scientist or research assistant).
Rat Poker Tours are poker tournaments where common courtesy rules are banned. Chip stealing, insults, physical violence are common and accepted as part of the game.
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:
The following list is alphabetical.