Guinea pigs, also known as cavies, experience the world largely through their teeth. This is a common behavior among rodents. They nibble to see if something is food or show affection. They play by nipping at each other. Biting and nibbling are two of the few ways they have to communicate.
Sometimes They Show Affection With Their Teeth
Guinea pigs, like many animals, groom each other. If your guinea pig likes you, he may try to groom you, as well. To groom a herd member, a guinea pig will dig into his fellow's fur with his teeth to dig out bugs, dirt, stuck food, and anything that might irritate a guinea pig's skin. You don't have any fur, but if your guinea pig is nibbling at you, it may be because he is trying to keep you clean and comfortable.
Sometimes They're Scared
Guinea pigs scare easily when exposed to loud noises. Vacuums, thunder, even loud clapping can frighten your guinea pig and make him want to get into his hide or burrow, where he feels safe. Cavies will also develop fears of people who regularly mishandle them. If your piggy was abused, he may even be frightened of people who resemble his abusers. During these times of heightened stress and fear, a guinea pig is more likely to bite.
Sometimes They're Hurt
Holding a guinea pig improperly, petting him the wrong way, petting him in a sensitive area, or just holding him too long can make him uncomfortable. A guinea pig needs to feel properly supported. Guinea pigs also prefer to do their business in private, so if your cavy needs to go, he's going to get uncomfortable and give you a little nibble to let you know.
Sometimes They're Hungry
Guinea pigs love treats. It's important to wash your hands before handling your guinea pig, especially if you've been handling food. If your hands smell like food, your guinea pig may bite before he realizes your fingers aren't a snack. He may also get excited and accidentally nip your fingers while you are feeding him treats.
Sometimes They're Just Plain Mean
Animals have personalities just like people do. Some guinea pigs have been raised in environments that don't encourage social behavior, and they're going to bite. There are also times when a normally sociable piggy has just been handled too much, or is in the middle of a game or snack, and wants to be left alone. Whatever the reason, when your guinea pig nibbles, it's because he's trying to tell you something.