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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. == 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 in the wild.〔(【引用サイトリンク】title=Habits, Habitat & Types of Mice )〕 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.〔(【引用サイトリンク】title=Creature Feature Rats )〕 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.〔(【引用サイトリンク】title=Competition in an invaded rodent community reveals black rats as a threat to native bush rats in littoral rainforest of south-eastern Australia )〕 Wild rodents, including rats, can carry many different zoonotic pathogens, such as ''Leptospira'', ''Toxoplasma gondii'', and ''Campylobacter''. 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. The average lifespan of any given rat depends on which species is being discussed, but many only live about a year due to predation.〔(【引用サイトリンク】title=How old is a rat in human years? )〕 The black and brown rats diverged from other Old World rats during the beginning of the Pleistocene in the forests of Asia. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Rat」の詳細全文を読む スポンサード リンク
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