Why is my Chihuahua biting his tail?

It could be because he is a really nervous dog, boredom or he has a “hot spot” dogs will scratch/chew at a bothersome hotspot. Try a different vet or visit a pet store. Get one of those big lamp shade looking collars to keep him from biting it and so it can heal. Then after it’s healed try getting a product called Bitter End that will keep him from biting. (same concept as the stuff nail biters use)

I don’t understand–your vet doesn’t tell you why? Did you ask him flat out or just accept pain killers and leave?

Go to a different vet, never heard of this problem. It could be a mental disorder the dog has. My friend’s dog constantly licked it’s paws until they bled when his brain started to deteriorate from cancer.

Go to a different vet, don’t take “i don’t know” or “no” for an answer!

mabe its bordem so take it outside for a while and play ball with it or mabe its fleas i would sugest going back to the vet or even writting a letter to dr Harry!