Rats are various medium-sized, long-tailed rodents. The best-known rat species are the black rat (Rattus rattus) and the brown rat (Rattus norvegicus). This group, generally known as the Old World rats or true rats, 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.
The term rat is also used in the names of other small mammals that are not true rats. Examples include the North American pack rats (aka wood rats) and a number of species loosely called kangaroo rats. 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, does, pregnant or parent females, dams; and infants, kittens or pups. A group of rats is referred to as a mischief.
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, some of which have become endangered due to habitat loss or competition with the brown, black, or Polynesian rat.
Skeleton of a black rat (Rattus rattus) on display at the Museum of Osteology. 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 microorganism 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 foot-and-mouth disease.
A rat in a suburb of Vancouver Rats become sexually mature at age 6 weeks, but reach social maturity at about 5 to 6 months of age. The average lifespan of rats varies by species, but many only live about a year due to predation.
The rat's larynx has been used in experimentations that involve inhalation toxicity, allograft rejection, and irradiation responses. One experiment described four features of the rat's larynx. The first being the location and attachments of the thyroarytenoid muscle, the alar cricoarytenoid muscle, and the superior cricoarytenoid muscle, the other of the newly named muscle that ran from the arytenoid to a midline tubercle on the cricoid. The newly named muscles were not seen in the human larynx. In addition, the location and configuration of the laryngeal alar cartilage was described. The second feature was that the way the newly named muscles appear to be familiar to those in the human larynx. The third feature was that a clear understanding of how MEPs are distributed in each of the laryngeal muscles was helpful in understanding the effects of botulinum toxin injection. The MEPs in the posterior cricoarytenoid muscle, lateral cricoarytenoid muscle, cricothyroid muscle, and superior cricoarytenoid muscle were focused mostly at the midbelly. In addition, the medial thyroarytenoid muscle were focused at the midbelly while the lateral thyroarytenoid muscle MEPs were focused at the anterior third of the belly. The fourth and final feature that was cleared up was how the MEPs were distributed in the thyroarytenoid muscle.
The black and brown rats diverged from other Old World rats in the forests of Asia during the beginning of the Pleistocene.
Species of rats are all found in Rodentia, and are present throughout the order. Typical rats are found in the genus Rattus.
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. Common terms rat and mouse are not taxonomically specific. Scientifically, the term rat is not confined to members of the Rattus for example, the pack rat.
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