A hamster grooming himself

Hamsters come in two sizes, full-sized hamsters which grow to 4-6 inches long and dwarf hamsters which are 2-3 inches in size.  Each size has several breeds, the main differences are in color and length of coat. Life expectancy is 2-3 years.

Besides size, the major difference between the two types of hamsters is that full size hamsters must be kept alone in a cage, while dwarf hamsters do best with a couple of cage mates (of the same sex and breed).  Dwarf hamsters are more active than full-sized breeds and actually require more space to be happy.

Hamsters are nocturnal by nature, which means they are most active at night.  Since they require lots of exercise, hamster wheels are a common cage accessory.  If the cage is kept in a bedroom, the sound of it being spun all night can drive a human inhabitant of the room crazy.  Their nocturnal nature can also lead to a cranky disposition during the day and they have been known to nip at people who disturb their sleep.