Gnome

Gnomes (Homunculus Gernumblus Gardensi) are a species of semi-sapient Little People.

Physical Description
The feet-tall Gnomes are small humanoids with brownish skin, round noses, bony feet, sharp teeth, and, perhaps most strikingly, a large potato-like overgrowth of their heads. Gnomes are hairless and rarely ever wear any clothes in the summer, though most graphical depictions politely skip over the more inappropriate parts of their anatomy, which are, in truth, visible.

Behaviour and Diet
Gnomes live in groups of about ten to fifty individuals. Being about as intelligent as the brighter Trolls, Gnomes are known to chat among themselves in an accented, bastardized approximation of the local human language. Gnomes mostly live in burrows known as gnome-holes, eating worms and roots for sustenance (though they will also gladly accept treats such as candy from humans).

Relationship with Humans
As Gnomes often invade wizarding gardens (magical plants being tastier to them than the natural kind), the rightful wizard owners of the land will often attempt to drive them out for the damage they cause, a process known as de-gnoming. The most popular method is to "uproot" the Gnomes, swing them around until they are dizzy and then throw them over the garden fence or wall. A crueller method (banned in some countries owing to Gnomes' relative sapience) is the use of Jarvey, a type of giant ferret bred by wizards, trained to devour gnomes on sight.

Habitat
Gnomes are native to Northerhn Europe, being found mostly in France and the British Isles, where they are confined to wizarding areas to protect the Statute of Secrecy. For instance, two groups of gnomes inhabited the Forbidden Forest and a particularly tricky bunch were the bane of the Weasley family's garden. There was also a population of gnomes in North America, presumed to have stowed away on human boats sailing from Europe.

Ministry of Magic Classification
Because of their status as pests and low intelligence, gnomes are classified as Beasts, and given the threat level of XX.

Canon

 * Gnome on the Harry Potter Wiki