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.
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.
