The worms you’re most likely to spot in your cat’s stool, vomit, or around their rear end fall into a few distinct categories, and each looks noticeably different. What you’re seeing (or what you might find) depends on the type of parasite, and identifying it helps determine the right treatment.
Tapeworm Segments: The Most Common Discovery
Tapeworm segments are by far the most frequently spotted parasite by cat owners, largely because they show up in obvious places. These flat, white segments are about a quarter inch long and roughly the size of a grain of rice. When fresh, they actively stretch and contract, so you may notice them crawling near your cat’s anus or on the surface of a fresh bowel movement. Once they dry out, they shrink to about 2 mm, turn hard and yellowish, and look more like sesame seeds.
You’ll often find dried segments stuck to the fur around your cat’s tail, on their bedding, or in spots where they regularly sit. The adult tapeworm itself stays inside the intestines and can grow several inches long, but you’ll almost never see the full worm. Instead, it sheds these individual egg-filled segments, which is what catches your eye.
Roundworms: Spaghetti-Like Strands
Roundworms are the other parasite cat owners commonly see with the naked eye, especially in kittens. They look like pieces of spaghetti or thin noodles: long, smooth, pale or cream-colored, and round-bodied. Adult roundworms typically measure 3 to 6 inches in length. You might see them in your cat’s stool or, more alarmingly, in vomit. They sometimes appear coiled or tangled together.
Kittens with heavy roundworm infections often develop a distinctive potbellied appearance, where the abdomen looks swollen and rounded even though the rest of the body may be thin. Other signs include a dull coat, vomiting, diarrhea, and poor appetite. Roundworm infections are extremely common in young cats because kittens can pick them up from their mother’s milk.
Hookworms: Too Small to Easily See
Hookworms are a common intestinal parasite in cats, but you’re unlikely to spot them yourself. Adults measure only about 10 to 15 mm long (roughly half an inch) and are very thin, making them difficult to see in stool without magnification. They’re typically white or grayish and hook-shaped at one end, which is how they anchor into the intestinal lining.
Because hookworms feed on blood, the clue you’re more likely to notice is a change in your cat’s stool rather than the worm itself. With heavy infections, feces often appear black and tarry due to digested blood. Weight loss and signs of anemia, like pale gums, are other red flags, especially in kittens.
Stomach Worms Found in Vomit
A less common but startling find is a stomach worm in your cat’s vomit. These parasites (Physaloptera species) attach directly to the stomach lining and are sometimes expelled when a cat throws up. Females can reach about 40 mm (roughly 1.5 inches), and males about 30 mm. They’re thinner than roundworms and typically white or pinkish. Immature worms are particularly likely to show up in the vomit of kittens.
Worms You Won’t See
Several important cat parasites are invisible to the naked eye. Lungworm larvae, for instance, are passed in feces but measure only about 400 micrometers, far too small to spot without a microscope. Cats with lungworm infections typically show coughing and breathing difficulties rather than visible worms.
Heartworms are large, white, spaghetti-like parasites that can grow to nearly a foot long, but they live inside the heart and blood vessels. You’ll never see them externally. Heartworm in cats causes respiratory symptoms that can mimic asthma, and diagnosis requires specific blood testing.
Whipworms, though uncommon in cats compared to dogs, are also too small and too deep in the large intestine to appear in stool visibly. For all of these parasites, diagnosis depends on a veterinary fecal exam that identifies microscopic eggs or larvae, not on what you can see at home.
What Your Cat’s Stool Can Tell You
Even when you can’t see actual worms, changes in your cat’s stool often signal a parasitic infection. Mucousy or bloody feces can indicate several types of intestinal parasites. Black, tarry stool points toward hookworms or another blood-feeding parasite. Chronic diarrhea, whether watery or soft, is one of the most common signs across nearly all worm types, as well as microscopic parasites like Giardia.
A single normal-looking stool doesn’t rule out worms either. Many infected cats pass eggs or larvae intermittently, which is why veterinarians often recommend checking multiple stool samples.
Quick Visual Comparison
- Tapeworm segments: Flat, white, rice-grain-sized pieces near the anus or in stool. Yellowish and sesame-seed-like when dried.
- Roundworms: Long (3 to 6 inches), smooth, pale, spaghetti-like strands in stool or vomit.
- Hookworms: Very small (about half an inch), thin, white. Rarely visible without magnification.
- Stomach worms: About 1 to 1.5 inches, thin, white or pinkish, found in vomit.
- Lungworms and heartworms: Not visible externally. Require veterinary testing.
Preventing Reinfection
Kittens should start deworming treatment at 2 weeks of age, with repeat doses every 2 weeks until they begin a regular parasite prevention program. For adult cats, the Companion Animal Parasite Council recommends year-round broad-spectrum parasite prevention. If year-round prevention isn’t possible, treating at least four times a year with a dewormer effective against intestinal parasites is the minimum recommendation. Indoor cats are at lower risk but not zero risk, since parasites can enter on shoes, other pets, or the occasional indoor hunting opportunity.