Types of worms found in dogs

A pot-bellied puppy, an itchy bottom or suspicious little "grains of rice" stuck to your dog's fur aren’t all caused by the same type of worm. In fact, the worms found in dogs vary hugely in their shape, size, lifecycle and the way they spread.

Learning a little about the different types of worms can help you understand how dogs pick them up and, perhaps most importantly, why finding the odd wriggler doesn't make you a bad dog owner. 

The three main types of worms found in dogs

Many owners have heard of roundworms and tapeworms, but there are actually three main types of worms found in dogs. 

1. Nematodes (roundworms)

Nematodes, often called roundworms, look similar to earthworms, although most species found in dogs are much smaller. This is the largest group of worms affecting dogs and, just to be confusing, includes a roundworm commonly referred to as roundworm, as well as hookworms, whipworms and lungworms. Aside from the aptly named lungworms, the majority of UK nematodes live in a dog’s intestines. 

2. Cestodes (tapeworms)

Tapeworms are flat, ribbon-like worms made up of many segments. Adult tapeworms live in the small intestine, and as the worm grows, new segments are continually produced behind the head. Older segments become filled with eggs before breaking away and passing out in your dog's poop. Occasionally you’ll see these white, rice-like segments stuck to the fur around your pup's bottom or in their bedding. But tapeworms rarely pass directly from one dog to another. While it’s almost always the adult that lives in a dog’s intestines, the eggs must first develop inside one or more intermediate hosts before they become infectious to dogs.

3. Trematodes (flukes)

Flukes are flat, leaf-shaped worms that are much less common in UK dogs than roundworms or tapeworms. They have complex life cycles involving intermediate hosts like snails and fish. Eating these or raw offal, specifically the liver, is how pet dogs become exposed. 

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A closer look at the main worms affecting UK dogs

Before looking at specific worms, if you’re interested in the signs to watch for, we have a separate blog on the symptoms of worms in dogs. 

Roundworms (Toxocara canis)

Roundworms are the most common intestinal worms in UK dogs, particularly puppies. Unlike many other worms, puppies can become infected before they are born or through their mother's milk. Adult dogs usually become infected by swallowing microscopic eggs from contaminated soil, grass or other environments where infected dogs have been.

Roundworms live in the small intestine, where they feed on what’s passing by. Low numbers cause few problems, but heavy burdens, particularly in puppies, can interfere with growth and digestion.

Hookworms

Hookworms are much smaller and less common than roundworms but attach firmly to the lining of the intestine and feed on blood. Dogs usually become infected by swallowing larvae from contaminated ground, although some species can also enter through the skin. While usually present in low numbers, they can cause anaemia, particularly in young puppies.

Whipworms

Whipworms live in the large intestine and have a distinctive whip-like shape, with a thin front end and a thicker tail. Dogs become infected by swallowing eggs that can survive in the environment for several years. Because the eggs are so hardy, contaminated gardens or kennels can remain a source of infection long after an infected dog has left.

Tapeworms

The most common tapeworm affecting pet dogs is Dipylidium caninum, often called the flea tapeworm. The eggs are eaten by flea larvae and then develop inside the adult flea, which dogs accidentally swallow while grooming. This is why effective flea control is an important part of preventing tapeworm infections.

Other tapeworms, including several Taenia species, have different intermediate hosts. Dogs with a strong hunting drive can be exposed by eating infected rodents or rabbits. Other dogs risk infection when they eat raw meat or offal from livestock carrying the larval stages.

Lungworms

Unlike many other nematodes (roundworms), lungworms don't live in the intestines. Although several different worms can affect the lungs and airways of dogs, the term lungworm is often used to refer to Angiostrongylus vasorum. 

Angiostrongylus vasorum spends its adult life in the heart and blood vessels supplying the lungs. Dogs become infected by eating slugs and snails or accidentally ingesting their slime on toys, water bowls or grass. Lungworm has become increasingly widespread across the UK over recent decades, making awareness and prevention more important than ever.

How dogs catch worms?

Different worms have evolved different ways of reaching their next host. Some wait around in the environment, while others rely on fleas, slugs or prey animals to complete their lifecycle. Here’s how most dogs catch worms:

1. From contaminated environments

Dogs don't have to eat fresh poop to become infected. Eggs can survive in the environment for months, even years, and are easily picked up while sniffing, licking paws or exploring.

2. From their mother

Toxocara roundworms are unusual because they can pass directly from mother to puppies during pregnancy or through milk after birth. It’s why worming is especially important for young puppies, and we have a separate blog on worming advice for puppies. 

3. From fleas

Fleas play an important role in the lifecycle of the most common tapeworm found in UK dogs. Dogs become infected by swallowing fleas carrying the immature stage of the tapeworm, which is why flea and worm treatments often go hand in hand. Find out more about how to get rid of fleas. 

4. From hunting or raw meat

Dogs that hunt, scavenge or are fed raw meat or offal have a greater chance of encountering certain tapeworms and, more rarely, flukes. Freezing raw meat or sourcing it from reputable suppliers can reduce some of these risks, although neither approach eliminates every parasite.

5. From slugs and snails

Lungworm has a different lifecycle from most intestinal worms. Slugs, snails and their slime carry the infective larvae, which dogs may swallow directly or accidentally while eating grass, drinking from puddles or picking up outdoor toys.

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Can dog worms infect people?

Some dog worms can infect people, but it’s uncommon and usually preventable. The roundworm Toxocara canis is the best-known example. People become infected by accidentally swallowing microscopic eggs from contaminated environments rather than catching worms directly from dogs. Simple hygiene measures such as washing hands after gardening, promptly picking up dog poop and following a worming programme help keep the risk very low.

A small tapeworm called Echinococcus multilocularis, found in parts of mainland Europe, can infect dogs travelling abroad and the eggs they shed can cause serious disease in people if accidentally swallowed. Dogs become infected by eating rodents and usually show few signs themselves. The larval stages of some Echinococcus species can form cysts within organs, making these parasites important for both animal and human health.

Emerging worms in the UK

While most of these worms are ‘the usual suspects’ that have been around for many years, warmer temperatures, changing weather patterns, international travel and imported rescue dogs are making it possible for new parasites to arrive and survive in the UK. 

Lungworm, for instance, is now found across much of the UK and is considered an important parasite for many dogs. Other worms, such as heartworm and Thelazia (eyeworm), remain uncommon in the UK but are occasionally diagnosed in dogs that have travelled abroad or have been imported from overseas.

Can you prevent worms?

Completely preventing every exposure to worms is almost impossible. Many eggs and sources of infection are effectively invisible. And as dogs naturally explore the world with their noses and mouths, their curiosity often overcomes caution. However, picking up poop when it’s still fresh, trying to prevent your pup gulping down that dead mouse they just found and effective flea control all help reduce exposure.

Routine parasite control also helps to keep worm numbers low enough that they are unlikely to cause disease. Remember, the most appropriate worming schedule depends on your dog's age, lifestyle and individual risk factors, so it's worth discussing this with your vet.

Conclusion

Different shapes, sizes, lifecycles and risks – not all worms are the same. Learning a little more about the different types of worms shouldn't give you nightmares. Instead, it helps explain why worms are an inevitable part of dog ownership and why finding the occasional parasite isn't a sign that you've done anything wrong.

The good news is that, while you may never know exactly when your dog has picked up a few unwanted passengers, it's straightforward to minimise the risk of them causing harm. Following a regular worming schedule, or using a test-and-treat approach where appropriate, can help keep worm burdens low so your dog stays happy and healthy.