Greyish-brown fur; prominent pointed muzzle, eyes, ears and long, almost naked, tail, about as long as the head-and-body. Much larger than any mice, but comparable with the much darker, shorter-tailed water vole in general size. Few survive more than 1 year in the wild but can live for around 4—6 years in captivity. The brown rat is a native of central Asia which was introduced to the British Isles around 1720. Brown rats are omnivorous, eating pretty much anything, from fruit and seeds to human food waste, insects, birds' eggs or even small mammals.

They are particularly common around towns and cities. Brown rats live in loose colonies and dig their own burrows. In the absence of humans, brown rats prefer damp environments, such as river banks. However, the great majority are now linked to man-made environments, such as sewage systems. It is often said that there are as many rats in cities as people, but this varies from area to area depending on climate, living conditions, etc. Brown rats in cities tend not to wander extensively, often staying within 66 ft of their nest if a suitable concentrated food supply is available, but they will range more widely where food availability is lower.