Cats can carry several different kinds of worms, and they do not look, behave or spread alike. The ten entries below are the worm types that veterinary parasite references name in cats: intestinal roundworms, hookworms and tapeworms, stomach worms, lungworms and one lung fluke. Only some of them are ever visible to an owner, and no worm can be identified with certainty by appearance alone. A veterinarian confirms infection with a test, and treatment depends on which parasite is involved.
How this list was chosen
Veterinary sources do not agree on a single ranking of the most common worms in cats, and the prevalence figures they publish vary by region, cat population and age. This article therefore does not claim that these are the ten most prevalent worms. It lists the ten named worms or worm groups that the veterinary references reviewed for this article describe as infecting cats, and it groups them by the part of the body they occupy. Where a worm is uncommon, localized or dependent on a particular exposure, the entry says so.
Two scope decisions shape the list. Protozoa, which are single-celled organisms and not worms, are excluded. Heartworm, Dirofilaria immitis, is also excluded because it is spread by mosquitoes and lives in the heart and lungs rather than in the intestines or other places an owner might encounter. It is a serious cat parasite, but it does not fit a list built around worms that can appear in stool, vomit or the respiratory tract. The lung fluke Paragonimus is included even though it is a trematode (a flatworm) rather than a roundworm or tapeworm, because it appears in Merck Veterinary Manual’s cat owner guidance alongside the other entries.
What kind of worms does my cat have?
The table gives the working picture for each entry. “Can an owner see it?” refers only to the worm or its segments, not to symptoms, which are covered in the entries below.
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| Worm | Where it lives | Can an owner see it? | Main caveat |
|---|---|---|---|
| Roundworms (Toxocara cati, Toxascaris leonina) | Intestine | Adults can be seen in vomit or stool | Many infections are found only by fecal examination |
| Hookworms (Ancylostoma species, Uncinaria stenocephala) | Intestine | Usually not | Can cause blood loss severe enough to cause anemia |
| Flea tapeworm (Dipylidium caninum) | Intestine | Segments may be seen | Routine fecal flotation can miss it |
| Prey-associated tapeworm (Taenia taeniaeformis) | Intestine | Segments may be passed; the reviewed sources do not describe their appearance separately | Cats may show few or no signs |
| Whipworms | Intestine | Not stated in the reviewed sources | Uncommon in cats in the United States |
| Ollulanus tricuspis (stomach worm) | Stomach | Not stated in the reviewed sources | Infections are described as sporadic |
| Physaloptera species (stomach worm) | Stomach | Not stated in the reviewed sources | Rare |
| Aelurostrongylus abstrusus (lungworm) | Lungs | Not stated in the reviewed sources | Diagnosis can be difficult |
| Eucoleus aerophilus (lungworm) | Lungs, as described by Merck Veterinary Manual | Not stated in the reviewed sources | Infective eggs are consumed with food or water |
| Paragonimus species (lung fluke) | Lungs | Not stated in the reviewed sources | Not a routine risk for every cat |
What do cat worms look like?
An appearance check is useful only for a few worms, and even then a look at the stool is not a diagnosis. A worm that looks like the description below may still be something else, and a worm that cannot be seen may still be present. Bring any suspected worm or segment to a veterinarian in a sealed container, and do not handle it with bare hands.
1. Roundworms: Toxocara cati and Toxascaris leonina
Adult roundworms are cream-colored and cylindrical. Cornell Feline Health Center describes adults as around three to five inches long. Because they are the largest worms on this list, they are the ones an owner is most likely to notice, typically as a worm passed in vomit or stool. Cornell’s page, last updated June 2018, gives an estimated range of 25% to 75% for roundworm infection among cats, with higher rates in kittens. That is an older estimate for the populations Cornell described, not a current figure for every region or cat population.
2. Hookworms: Ancylostoma species and Uncinaria stenocephala
Hookworms are small and slender, and they are usually not visible in stool. An owner is unlikely to identify them by sight, so the signs of infection are more useful clues than the worm itself. Those signs are covered in the section on symptoms below.
3. Flea tapeworm: Dipylidium caninum
For this tapeworm, the useful picture is a segment, not the whole worm. Fresh segments may resemble grains of rice, and dried segments may resemble sesame seeds. Segments may be seen on the fur around the tail or in fresh stool, and they can look like something else until they dry. If you see something that might be a segment, a veterinarian can assess it, but a segment alone does not show how heavy the infection is.
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4. Prey-associated tapeworm: Taenia taeniaeformis
This tapeworm is acquired by eating infected prey, not by swallowing fleas. Cats with this infection may show few or no signs, so the first sign may be a segment, or the infection may only be found during testing. The reviewed sources do not describe the segments of this species separately from other tapeworms, so an owner should not assume a particular appearance means a particular tapeworm.
5. Whipworms
Whipworms are uncommon in cats in the United States. Heavy infection may cause diarrhea, which is the main reason they are worth knowing about. They are not one of the infections most often seen in cats, and an owner should not expect to identify one by eye.
6. Stomach worm: Ollulanus tricuspis
Infections with this stomach worm are described as sporadic. Vomiting and weight loss may occur. Diagnosis may involve examining vomit, which is one reason that persistent vomiting should be reported to a veterinarian rather than assumed to be a diet problem.
7. Stomach worm: Physaloptera species
This group of stomach worms is rare in cats. Infection is associated with insects or transport hosts, such as mice, which are the routes a veterinarian would consider when taking a history.
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8. Lungworm: Aelurostrongylus abstrusus
This lungworm is acquired when cats eat prey that has itself eaten infected slugs or snails. Coughing and difficulty breathing can occur. Diagnosis can be challenging, and a negative result does not always settle the question, so a cat with respiratory signs and a history of hunting may need repeated assessment rather than a single test.
9. Lungworm: Eucoleus aerophilus
Merck Veterinary Manual identifies this as another feline lungworm. Its eggs are infective, and cats may take them in with food or water. Signs are similar to those of other lungworms, which is why a respiratory picture alone does not identify the species.
10. Lung fluke: Paragonimus species
This is a trematode, a flatworm that is not a roundworm or a tapeworm. In cat owner guidance it is associated with eating raw crayfish or crabs. It is not a routine risk for every cat, and an owner whose cat has no access to raw crustaceans is unlikely to be exposed to it.
How do cats get worms?
Routes of infection differ by worm, and several worms have more than one route. The most useful way to think about them is by how the worm reaches the cat:
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- From mother to kitten: roundworms may be passed to kittens, which is one reason kittens have higher rates in the Cornell estimate above.
- From eggs in the environment: roundworms can be acquired through eggs, and Eucoleus aerophilus eggs are consumed with food or water.
- Through the skin: hookworm larvae may penetrate skin, and hookworms can also be swallowed.
- By swallowing fleas: the flea tapeworm Dipylidium caninum is acquired when a cat swallows an infected flea while grooming.
- By eating prey: Taenia taeniaeformis follows eating infected prey, and Aelurostrongylus abstrusus follows eating prey that has eaten infected slugs or snails. Roundworms may also be acquired through prey.
- By eating insects or transport hosts: Physaloptera species are associated with insects or hosts such as mice.
- By eating raw crustaceans: Paragonimus species are associated with raw crayfish or crabs.
The reviewed sources do not state the route of infection for whipworms or Ollulanus tricuspis, so this article does not assign one.
Signs to watch for, and when to call a veterinarian
Many cats with worms show few or no obvious signs. When signs do occur, they are nonspecific and overlap across worm types. Possible signs include:
- Vomiting or diarrhea
- Weight loss or poor growth, particularly in kittens
- A pot-bellied appearance
- Anemia, including pale gums
- Dark, tarry stool, which can accompany severe blood loss from hookworms
- Coughing or difficulty breathing
- Visible worms or segments in vomit, stool or around the tail
Some signs need prompt attention rather than a wait-and-see approach: persistent vomiting or diarrhea, weakness, pale gums, breathing difficulty, or a kitten that is not growing normally. An owner should contact a veterinarian rather than treating these at home.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.How do vets diagnose worms in cats?
The diagnostic approach depends on the suspected parasite. Veterinary testing may include fecal testing and microscopy, antigen tests, PCR, imaging, or examination of vomit. The same stool sample can miss some infections, so a single negative result does not rule out every worm.
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- Fecal flotation can miss tapeworms. Tapeworm eggs and segments may be unevenly distributed, so a negative routine fecal flotation does not always rule out infection with a tapeworm.
- Lungworm larvae are hard to find consistently. For this reason, a respiratory cat may need more than one test or a different test.
- Kittens need more frequent testing. The Companion Animal Parasite Council’s feline hookworm guidance, last updated February 28, 2025, recommends more frequent testing for kittens than for adults. The right frequency depends on a cat’s health and lifestyle, so the schedule should be set with a veterinarian.
- Older guidance on tapeworms. The Companion Animal Parasite Council’s cestode guidance was last updated November 1, 2016. It is useful background on tapeworm diagnosis, but a veterinarian will apply current testing practice.
How are worms treated?
Treatment depends on the parasite, and no single dewormer covers every worm on this list. The steps below describe the process rather than a dose.
- Book a veterinary visit and describe the cat’s symptoms, diet, outdoor access, prey access and flea status. Bring a fresh stool sample if the cat has diarrhea or if a worm was seen.
- Ask the veterinarian which parasite is suspected or confirmed, and which tests will confirm it.
- Follow the veterinarian’s prescription and the product directions exactly. Cornell reports that treatment of gastrointestinal parasites often requires a medication prescribed by a veterinarian.
- Ask about prevention of reinfection. This may include flea control, limiting access to prey and cleaning up cat waste, depending on the worm.
- Ask when the cat should be retested. Kittens may need more frequent testing, as noted above.
Do not give a cat a dewormer intended for another species or for a different worm, and do not assume that a product that worked for one cat is right for another.
Preventing reinfection
Prevention is mostly about breaking the routes described above. Practical steps include:
- Remove feces promptly from the yard and litter box.
- Clean the litter box frequently.
- Wash hands after handling cat waste.
- Limit hunting or scavenging where possible, especially for cats that catch rodents or birds, slugs, snails, insects or crustaceans.
- Control fleas, which is the clearest preventive step against the flea tapeworm Dipylidium caninum.
These steps reduce exposure but do not guarantee a worm-free cat, and reinfection can follow ongoing exposure even after treatment.
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