Get rid of these parasites. Then, bathe your dog with a medicated shampoo and give him some medication for the itching. A dog will chew at a burr, a thorny stick that is caught in his fur, or a thorn in his paw. He will try to untangle matted fur by chewing on the fur mat. For long-haired dogs, regular grooming is necessary.
Some dogs suffer from food allergies which can result in excessive licking.
If you suspect diet, ask your veterinarian to recommend a non-allergic dog food. If the licking stops, slowly introduce one food at a time, carefully checking the ingredients. Try to determine which ingredient is the culprit. If excessive chewing and licking are not due to health problems, then take a close look at your relationship with your dog. If your dog is shy, introverted, or is quick to go into submission, and there is stress because of his relationship with you, he will likely direct his attention inwardly.