Dogs normally use their teeth as part of daily grooming. This often involves very fast chewing-like motions at the base of the tail and pulling at any matted hair with the teeth. This can be done once or several times a day, depending on the dog. But if the dog suddenly begins chewing around the tail a lot more than usual, he needs medical attention.
Under the Tail
If the dog is chewing under the tail around the rectum, then he could have impacted anal glands. The dog will also "scoot," or drag his rear end on the carpet or grass, his hind paws off of the ground and the forelegs doing all of the work. According to The Veterinarian's Guide to Your Dog's Symptoms, unaltered male dogs can develop painful growths in this area. The dog will lick and chew in order to clean up the blood.
Although the contagious fungal infection ringworm is not itchy to start with, as it progresses any round bald spots will get itchy. The Dog Owner's Home Veterinary Manual notes that ringworm first settles on the face, paws and tail of a dog before spreading to other parts of the body. Check the dog for round bald patches.
The rectum is a warm spot on the dog, ideal for lice, fleas and other parasites. Dogs going after a flea will often bare his teeth before chewing at the itch. But if a dog is scooting and chewing around the tail and does not have impacted anal glands or rectal tumours, check for what looks like grains of rice around the his rectum, tail and hind legs. These are signs of a tapeworm infestation.
Docking is the practice of cutting off a dog's tail, bone and all. Docking a dog's tail is illegal in many countries, but still legal in the United States. According to the World Small Animal Veterinary Association, one of the complications that may come from docking is improper healing, which causes incredible itching from the rump to the remaining tail stump. The dog can open up the skin and become infected. Painful growths caused by scar tissue can also result.
If there are no medical reasons why the dog constantly keeps chewing or licking on the tail or around the base of the tail, then he has developed a compulsive behaviour or bad habit. The act of chewing has become pleasurable. The ASPCA recommends giving these dogs more exercise and more interaction with their owners to distract them from tail-chewing.