social animals, and live in groups in the wild. They rely on their sense of smell to identify other members of their clan, so it is important to use what is commonly referred to as the "split tank method" (or splitcaging) when introducing gerbils from separate litters. Gerbils are known to attack and often kill those carrying an unfamiliar scent. As pets A gentle and hardy animal, the Mongolian gerbil has become a popular small house pet. It was first brought from China to Paris in the 19th century, and became a popular house pet there. It was later brought to the United States in 1954 by Dr. Victor Schwentker for use in research. Dr. Schwentker soon recognized their potential as pet animals. Selective breeding for the pet trade has resulted in a wide range of different color and pattern varieties. Gerbils became popular pets in the US around the late 1950s and were imported to the United Kingdom in 1964, where they became popular pets too. They are now found in pet shops throughout the UK and the US. However, due to the threat they pose to indigenous ecosystems and existing agricultural operations, it is illegal to purchase, import, or keep a gerbil as a pet in the U.S. state of California. It is also illegal to import the animal into New Zealand. Housing in captivity Mongolian gerbils prefer to live in pairs or groups rather than alone. They are social and gentle, and do not bite readily. As diggers and tunnel-makers they are better suited to a tank with a deep substrate or bedding rather than a hamster cage, since the absorbent substrate is liable to be kicked up and out of a cage quickly. Mongolian gerbils like to chew objects to file their perpetually growing teeth, like all rodents, and need plenty of cardboard items and chew toys; the cardboard will be chewed up in to bedding and mixed with the substrate. Plastic toys and tunnels should be avoided in-case of ingestion. Fresh vegetables should be included in small amounts as an excess may cause diarrhoea. Some vegetables are toxic to gerbils, including potatoes, onions, cabbage; a diet based on multiple seeds, e.g millet and alfalfa pellet mix is sufficient. Water should be provided with a drip-feed system to prevent accidental build-up of harmful mould in the tank environment. Care should be taken not to introduce new