A Primer On Intestinal Worms: Types, Symptoms, and Diagnosis of Intestinal Worms in Dogs

Intestinal worms in dogs are parasites that live in the digestive tract. They cause damage and rob your dog of needed nutrients. 

The damage they cause depends on the type and number of worms involved. In general, the adult worms that infect dogs cannot live in people. However, in rare cases, immature forms of these parasites can migrate through human tissue. As a result, they can cause inflammation and potentially serious problems, especially in delicate tissues like the brain or eye.

A Primer On Intestinal Worms: Types, Symptoms, and Diagnosis of Intestinal Worms in Dogs


The four common intestinal worms in dogs are:

  • roundworms
  • hookworms
  • whipworms
  • and tapeworms


Roundworms are long, white worms that look like strands of spaghetti. 

Roundworm infections are most common in puppies. This is because puppies often contract the worms directly from their mother (through the womb or mother’s milk).

However, dogs of any age can contract roundworms from eggs deposited with feces.

A Primer On Intestinal Worms: Roundworm
Roundworm; 2-3 inches

Adult worms live in the small intestine, stealing nutrients and irritating the digestive tract. Large numbers of roundworms can even block the digestive tract. Sometimes, coiled-up white worms are visible in the material that your dog vomits or in the feces, which may be diarrhea. Puppies infected with large numbers of worms often have trouble gaining weight and may have “potbellies” and a dull hair coat.


Hookworms are tiny parasites that “chew” their way into the intestinal wall, attaching and feeding on blood. 

Infection often takes place directly from the mother to the puppies. However, dogs can also contract them by eating contaminated soil or even by skin contact with it.

A Primer On Intestinal Worms: Hookworm
Hookworm; `1/8 inch

Hookworms are very small, so you can’t see them in fecal material. But infected dogs usually develop diarrhea that may be black and tarry from digested blood.


Whipworms get their name from their long, slender bodies capped with a small club-like end. 

These worms lie coiled within the wall and lining of the large intestine. Dogs contract whipworms from eggs that are deposited with feces. In cases of light infection, dogs may not show any signs. However, with heavier infections, dogs often develop diarrhea that may have red blood in it.

A Primer On Intestinal Worms: Whipworms
Whipworm; 3-6 inches


Tapeworms are long, segmented white worms that live within the digestive tract. 

The worm’s head embeds itself into the digestive tract lining, with the rest of the worm trailing downstream and absorbing nutrients that pass by.

Segments filled with egg packets break off the worm’s body and make their way outside with feces.

A Primer On Intestinal Worms: Tapeworm
Tapeworm; ~8 inches

There are two common types of tapeworms:

  • one has segments that are shaped like grains of rice or tiny pumpkin seeds
  • the other looks like a flat, narrow ribbon that is segmented into smaller squares or rectangles.

Dogs are commonly infected with the first type by eating fleas that contain immature tapeworms. Therefore, this type of tapeworm infection means a flea infestation is also likely.

Dogs can also become infected with the second type of tapeworm by eating infected rodents or other prey. You might discover dry segments of either kind of tapeworm stuck to hairs around your dog’s anal area. Many infected dogs show no signs. If they do, the symptoms include:

  • vomiting
  • diarrhea
  • and large numbers of tapeworms can rob your dog of the nutrients it needs.

Diagnosing intestinal worms in dogs

Your veterinarian can examine a sample of your dog’s feces under the microscope to look for eggs of the various intestinal worms. 

Often, multiple fecal samples collected on different days need to be examined to find the eggs. Many medications are available to treat the various types of worm infections. Depending on where the worms are in their life cycle, more than one treatment is often needed.

Keep your yard and your cat’s litter boxes clear of feces. That helps limit the number of worm eggs in the environment that can reinfect your dog.

Related articles:
Abdominal Distention in Dogs: Why Is My Dog’s Stomach Swollen?

Further reading:
Internal Parasites in Dogs
How to Tell If Your Dog Has Worms

Share your thoughts