This breed, descended from working Terriers, has a lot of energy, tenacity, and aggression towards its prey, which was originally the fox and other, smaller animals such as squirrels. It needs regular exercise, although its size makes it a good apartment pet. Many of these dogs have skin allergies, and its personality is more excitable than even some other terriers. They are alert and consider themselves guard dogs, although their size prevents them from providing any real intimidation. They are independent thinkers and must be trained firmly from an early age.