Your dog may have worms even though you see no evidence of them.
With the exception of tapeworms, which may be effectively diagnosed visually, the best way to diagnose worms in your dog is to have your veterinarian perform a fecal exam. Your veterinarian will examine your dog's feces under a microscope for the presence of microscopic worm eggs. However, your dog may have worms, yet show no eggs in the stool. This is why regular deworming with a wormer (prescription or non-prescription) is so important. Be sure to take your dog for regular fecal exams to detect the presence of species of parasitic worms, which may not be killed by our usual wormers. And be sure to talk to your veterinarian before giving your dog a non-prescription wormer.
Common Types of Worms:
Roundworms- The most common parasite of the digestive tract in dogs - are several inches long, look like spaghetti, and may occasionally be seen in the stool or vomit of an infected dog. Usually, though, you will not see them.
Hookworms and Whipworms - Additional parasitic pests, are very small and virtually impossible to see in the stool or vomit.
Tapeworms - If you look closely, you may be able to see segments of tapeworms moving around your dog's anal area. If dried, they may appear as rectangular segments similar in size to a grain of white rice or a cucumber seed.