Hamsters are rodents belonging to the subfamily Cricetinae. The subfamily contains about 25 species, classified in six or seven genera. Hamsters are crepuscular and remain underground during the day to avoid being caught by predators. In the wild, they feed primarily on seeds, fruits, and vegetation, and will occasionally eat burrowing insects. They have elongated cheek pouches extending to their shoulders in which they carry food back to their burrows.Hamster behavior varies depending on their environment, genetics, and interaction with people. Because they are easy to breed in captivity, hamsters are often used as laboratory animals. Hamsters have also become established as popular small house pets, and are sometimes accepted even in areas where other rodents are disliked, and their typically solitary nature can reduce the risk of excessive litters developing in households.The species of genus Phodopus are the smallest, with bodies 5.5 to 10.5 cm (2.2 to 4.1 in) long; the largest is the European hamster (Cricetus cricetus), measuring up to 34 cm (13.4 in) long, not including a short tail of up to 6 cm (2.4 in). The Angora hamster, also known as the long-haired or teddy bear hamster, which is a type of the golden hamster is the second-largest hamster breed, measuring up to 18 cm (7.1 in) long.
From : http://en.wikipedia.org/wiki/Hamster