Symptoms of worms in dogs include loss of hair, loss of appetite, diarrhea, dull coat, dehydration, vomiting, cough, and blood in stools. Some dogs may develop pot bellies as a result of worm infestation. In severe cases, these worms may appear in the stools of your pet. While some types of dog worms are visible to the naked eye (may be present in stools and sometimes on fur), others require microscopic testing.