The earliest and most common gerbil kept as a pet is the Mongolian gerbil. Given their friendly, inquisitive nature and cleanliness, it is easy to understand their popularity. They are well known for being reluctant to bite (only when very threatened or afraid), which makes them appealing for households with children, though as with all pets, children should be supervised when handling them. Gerbils prefer to live in groups, and same-sex littermates tend to get along quite well -- however, use caution and common sense when introducing gerbils that do not know each other. For housing, the American Gerbil Socity recommends a 10 gallon aquarium with sealed, but well-ventilated top for 2 gerbils, filled 1/3 of the way with bedding (preferably Aspen, Corn Cob, or Carefresh bedding), which allows them room to dig tunnels, as they naturally do in the wild. They also should have a water bottle, nesting box, toys, and exercise wheel (though your gerbil may find other ways of burning off energy, and ignore it). Gerbils will do well on a commercial food mix, supplemented with timothy hay, fresh fruit and vegetables, some nuts (sparingly) and protein (live mealworms, crickets, hard boiled eggs), and can live up to 4 years.