There are actually two main types of vipers-the true vipers and pit vipers. Pit vipers live in Asia and the Americas. The name comes from a small hollow in the side of the head just below the eye. The small hollow, or pit, has a special nerve that senses heat, helping the pit viper to find its warm-blooded prey. True vipers don’t have this special nerve and must rely on their keen sense of smell to find their food. Vipers don’t usually strike unless they are disturbed or are looking for food. Still, it is a good idea to stay away from them.