Maybe if you just got your guinea pig, he is scared. He just needs to get used to you, so give him lots of attention!
Maybe he's just scared. I'd try just leaving your hand in the cage for a few minuets each day and eventually start to touch him. Don't pick him up right away. Once he's used to you and your "smell" then maybe he'll stop biting. I had a hamster once who bit me all the time, and this really helped! Good luck!
Do you keep "gnawing sticks of wood" in the cage? The wood must be untreated wood and can be bought at most pet supply stores. Guinea pigs (like other rodents) need materials like wooden sticks to keep their teeth worn down. If they don't have them, the top teeth will grow so long that the little fella cannot eat. Many will bite hoping that you will notice its teeth and help them. There may be guinea pigs who are ill-tempered to both people and other little animals. If he were mine, I would thump him on the nose gently to stop its biting and see if that would let him know I don't like his behavior. They can be taught just like any other pet if you interact with them a lot. They are very gregarious as a rule, and enjoy company and playful companionship.
Hope this helps.
Julia in Orlando
If you have been handling food and then your guinea pig, he might think you smell like food. Wash your hands before handling. This also works with hamsters and gerbils. Also, if you come at an animal from above it scares them, so put your hands low and approach slowly. Hope this helps.
My daughter had 3 guinea pigs. One of them was always a biter & kind of mean. The others were mellow.
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