Chihuahuas are the world's smallest breed of dog. They are cute and cuddly on the outside, but when you make them angry, like any other dog, their bite can land you in hospital. They were named after the state of Chihuahua in Mexico. Both males and females are under 3 kilograms, and because of their tiny size, they can live up to 18 years. Small dogs are most definitely likely to live longer than larger dogs.