Dogs biting their tails and spinning around may be caused by bored play, skin diseases or parasites in their tails, or problems with their anal glands. It is best to check your dog’s tail first to see if there are any skin diseases or parasites. If you have worms, you also need to check whether the anal glands are inflamed, red and swollen. If so, you need to treat the dog in time. If the dog only has this situation occasionally, then it is just boring and playing, so don’t worry.