Wild rats, also called Norway rats, brown rats or sewer rats, originated in northern China. They have spread to every continent except Antarctica and have been domesticated for centuries. Domestic rats, referred to as fancy rats, are the same breed as their wild counterparts. Despite their identical genetic make-up, wild and domestic rats have many differences.
Look at the rat's colouring. Most wild rats are dark brown or black, although a few have white underbellies. While some domestic rats are these colours, too, many are grey, white, light brown or a combination of these colours.
Look at the rat's physical condition. Most domestic rats are somewhat plump, with soft fur and probably no scars. Wild rats, which must struggle to find food and keep in shape to flee from predators, are usually thinner and have rougher coats. They are also more likely to have scars from run-ins with predators and other rats.
Study the way the rat acts around you. If it runs away with its fur puffed out when you approach, it is probably wild. Even when frightened, a domestic rat is likely to approach you if you offer it food and speak to it in a soothing voice.
Examine the way the rat acts when it doesn't know you are nearby. Wild rats move swiftly, with their ears stiff and their eyes wide open. Domestic rats usually appear more relaxed.
If you have determined the rat is domestic and want to catch it, wear thick gloves. The animal could try to bite.