Pets can add a lot to your household, but some add more work, stress and cost than others. Some can be outright dangerous, while others will outlive you. Here's a list of pets you might not want to own.

1. Monkeys

Sure, they're adorable, but they're wild animals. Many states (currently 20) ban keeping them as pets. Many monkey lovers keep them anyway, treating them as babies. The problem is: the babies grow up and become belligerent adults. They are unpredictable and can bite or attack you and your children. Monkeys can live up to 40 years, which is a huge commitment for a pet, and it can be difficult to find a vet who will treat their many medical problems.

Monkeys are messy and expensive. You need a large cage to keep them happy but prevent them from roaming around your home and destroying it. You're better off leaving them at the zoo.

2. Horses

While the average person won't have a horse in their apartment, horses do require a lot of attention and money. Just like any other pets, they need vaccines and vet visits, but they also need trips to the dentist and blacksmith, as well as regular worming appointments. If you can't drive your horse to these appointments, you'll have to pay for the service provider to visit your horse. 

Horses require constant grooming and exercise. If you live on a farm, this may be easy, but if not, you may be unprepared for the amount of time you'll need to put into feeding, brushing and riding your horse. Many people are eager to take care of a horse at first, but the novelty often wears off. Instead, consider paying to ride a horse on a per-visit basis. It's more fair to the horse.

3. Tortoises

Tortoises may be cute, but they can outlive you and outweigh you. Some can live to be 100 years, which means you'll have to include yours in your will to pass on to a family member! Tortoises are particular about their habitat, so you'll need to fix up your back yard to accommodate, or get a tank that will hold yours (until he grows). If you want something cute and cuddly, a tortoise isn't it. Tortoises can also have some health problems, so lugging yours to the vet could be a backbreaking event!

4. Vicious Dogs

While each dog has his own personality, certain breeds can be harder to control. Some breeds, like pit bulls, doberman pinschers and rottweilers can be aggressive if they are unsure of a situation. While there are plenty examples of these dogs living in harmony with families, there have been cases where the dog felt cornered and attacked a child or family member. If you do buy one of these breeds, do your research to learn how to train them and always teach your kids to not get in the dog's face. Respecting the dog will help the relationship along.

5. Ferrets

While they're cute and cuddly, ferrets don't make great pets. They act like they're on caffeine all the time, which leaves little down time for you to relax. Ferrets are notorious for stealing things, so if you brave parenting one, expect to find things "misplaced" all over your house. They can chew holes and hide, making them even more frustrating. They can also bite people and other pets, like dogs.

6. Pot Bellied Pigs

If you're having visions of owning a little "Wilbur" pig, think twice. The tiny piglets you've seen on tv grow big -- up to over 100 pounds! And you have to feed it a lot of food, which can be expensive. They also need regular hoof care to keep their hooves healthy. They are at risk of many health problems, including parasites and mange. Pot bellied pigs don't usually get along well with children, so if you're considering adding a pig to your household, realize that there will be some struggles for power among the two, which may result in your child getting hurt.

There are many people who own these types of pets and love them, but fair warning: you're in for more work and stress than you'd be with a goldfish! Research your pet-to-be's personality and temperament so that you are prepared for what may come.

Photo: Flickr user mrpattersonsir. Creative Commons 2.0.