16. Chihuahua

Considering the fact that the Chihuahua is the smallest known breed to man, there is a reason why it has found itself on this list. Originating from Mexico, and named after the state with the same name, these tiny little dogs are easily provoked, and therefore may attack just as quickly as they bark. The term “small but terrible” describes them perfectly as they have no patience for younger kids, and normally are loyal to only one person.

17. Caucasian Ovcharka

This particular dog requires a lot of training from the time that it is a puppy until it is considered an adult. This powerful canine needs to be socialized early on, as some do not take to humans or other animals easily for that matter. Although they are typically relaxed animals when resting, they do have a tendency to be quite territorial and aggressive when not trained and fraternized properly.