Rats are various medium-sized, long-tailed rodents in 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.


A brown rat in NYC. image: G. Scott Segler/wikimedia

Taxonomy of rats

Kingdom: Animalia

Phylum: Chordata

Class: Mammalia

Order: Rodentia

Family: Muridae

Subfamily: Murinae

Genus: Rattus

64 species

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 muridae 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.

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 in the wild.

Rats that are not really rats

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. 

Groups of rats

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.

Rats are often survivors or they can be endangered

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.

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.

Diseases that rats can carry

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.

Rat tails are quite interesting

The characteristic long tail of most rodents is a feature that has been extensively studied in various rat species models, which suggest three primary functions of this structure: 

  • thermoregulation, 
  • minor proprioception, and 
  • a nocifensive(pain)-mediated degloving response. (they lose their outer part of tail but only in extreme pain/emergencies)

Rodent tails—particularly in rat models—have been implicated with a thermoregulation function that follows from its anatomical construction. This particular tail morphology is evident across the family Muridae (in contrast to the bushier tails of the squirrel family, Sciuridae). 

The tail is hairless and thin-skinned, but highly vascularized, thus allowing for efficient counter-current heat exchange with the environment. The high muscular and connective tissue densities of the tail, along with ample muscle attachment sites along its plentiful caudal vertebrae facilitate specific proprioceptive senses to help orient the rodent in a three dimensional environment. 

Lastly, murids have evolved a unique defense mechanism termed "degloving" which allows for escape from predation through the loss of the outermost integument layer on the tail. However, this mechanism is associated with multiple pathologies that have been the subject of investigation.

Pet rats

Specially 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 from 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 or dogs. Tamed rats are generally friendly and can be taught to perform selected behaviours.

The most common pet rats are also known as Fancy rats (Rattus norvegicus)


3 week old young domestic pet rats image: Waldemar Zboralski/wikipedia

Source adapted from: Wikipedia contributors. (2018, July 22). Rat. In Wikipedia, The Free Encyclopedia. Retrieved 01:48, August 6, 2018, from https://en.wikipedia.org/w/index.php?title=Rat&oldid=851525092