Worms are one of the most common health problems in dogs, and one of the easiest to miss. Many infected dogs look and act completely normal. The signs, when they do appear, are easy to wave off as a bad meal or a one-off upset stomach. This guide walks through what worms actually look like in a dog, the main types you’ll hear about, why a vet visit beats a guess at the pet store, and how to protect both your dog and the people in your home.
The short answer
If you see small white worms or dried, rice-like segments near your dog’s rear or in their stool, your dog very likely has worms — most often roundworms or tapeworms. But the absence of those signs does not mean your dog is clear. The reliable way to know is a fecal test at your veterinarian, because different worms need different medicines and some never show up to the naked eye at all.
One worm stands apart from the rest: heartworm. It does not live in the gut, it won’t show up in a fecal test, and it can be fatal. We cover it separately below because the prevention-versus-treatment math is very different.
Signs of intestinal worms
Intestinal worms — the ones that live in the digestive tract — can produce a range of signs, or none. Watch for:
- Visible worms in stool or vomit. Roundworms look like spaghetti; tapeworms shed flat segments.
- Rice-like segments near the rear, in bedding, or stuck to the fur around the tail — a classic sign of tapeworm.
- Scooting or dragging the rear along the floor, often from tapeworm segments causing irritation.
- A pot-bellied, swollen appearance, especially in puppies with a heavy roundworm load.
- Diarrhea, sometimes with mucus or blood (blood points more toward hookworm or whipworm).
- Weight loss despite a normal or increased appetite.
- A dull coat, low energy, or poor growth in puppies.
The Merck Veterinary Manual notes that many infections, particularly mild ones in adult dogs, cause no obvious clinical signs at all. That is exactly why you can’t rely on watching and waiting.
How dogs pick up worms
Dogs get worms through ordinary daily behavior, not bad luck or neglect:
- From their mother. Puppies can be born with roundworms passed in the womb, or pick up roundworms and hookworms through their mother’s milk. This is why the Companion Animal Parasite Council (CAPC) recommends deworming puppies starting at a few weeks of age.
- From the environment. Roundworm, hookworm, and whipworm eggs or larvae survive in soil, grass, and feces. A dog sniffing, licking, or walking through a contaminated yard or park can ingest them — hookworm larvae can even burrow through the skin of the paws.
- From fleas (tapeworm). The most common tapeworm spreads when a dog swallows an infected flea, usually while grooming. No flea problem, far less tapeworm risk — which is why flea control is part of worm prevention. (See our guide on fleas on dogs and how to get rid of them.)
- From hunting or scavenging. Eating rodents, rabbits, or raw prey can transmit certain tapeworms and other parasites.
- From mosquitoes (heartworm). Heartworm is in a category of its own — see below.
Common worms at a glance
| Worm | How it spreads | Key sign | Note |
|---|---|---|---|
| Roundworm | Mother to pup, contaminated soil/stool | Spaghetti-like worms; pot belly in pups | Zoonotic — can infect people |
| Hookworm | Soil/stool, skin penetration, mother’s milk | Bloody/dark diarrhea, anemia, weakness | Zoonotic; dangerous in young pups |
| Tapeworm | Swallowing an infected flea | Rice-like segments near rear; scooting | Treat the fleas too, or it returns |
| Whipworm | Contaminated soil/stool | Watery or bloody diarrhea, weight loss | Hard to detect; eggs shed irregularly |
| Heartworm | Mosquito bite | Cough, fatigue, exercise intolerance | Lives in the heart/lungs; potentially fatal |
Why a vet fecal test matters
It’s tempting to grab an over-the-counter dewormer and call it done. Here’s why that often falls short:
- Different worms need different drugs. A product that clears roundworms may do nothing for tapeworms or whipworms. Without knowing what you’re treating, you’re guessing.
- OTC dewormers don’t cover everything. Many pet-store products target only the most common worms and miss others entirely. Some require repeat dosing on a schedule to break the life cycle, which the label may not make obvious.
- Eggs are invisible to you. Whipworms, in particular, shed eggs irregularly, so even a microscope exam can miss them on a single sample. A vet may recommend testing more than once.
- Dosing should be vet-directed. Correct medication, dose, and timing depend on your dog’s weight, age, and the specific parasite. We’re deliberately not listing doses here — that’s a conversation for your veterinarian, who can also flag drug sensitivities in certain breeds.
A fecal test is inexpensive, quick, and takes the guesswork out. CAPC recommends fecal testing several times in a dog’s first year and at least once or twice a year for adults.
Heartworm is different — and serious
Heartworm deserves its own section because almost nothing above applies to it. Heartworms are transmitted by mosquito bites, not soil or fleas. The larvae mature into worms that live in the heart and lungs, where they damage these organs over months to years. Early on there are no signs; later, dogs may show a soft cough, tiredness, reluctance to exercise, or weight loss.
Two points the Merck Veterinary Manual and CAPC both stress:
- A fecal test will not find heartworm. It requires a specific blood test at the vet.
- Prevention is far easier, cheaper, and safer than treatment. Treating an established heartworm infection is a long, expensive, and risky process involving strict rest and a series of injections. Prevention is a simple monthly or longer-acting product.
Because mosquitoes are active in more seasons and regions than people assume, CAPC recommends year-round heartworm prevention for all dogs, in every state. Many preventives also control intestinal worms, doing double duty.
The risk to people (zoonosis)
This is the part worth taking seriously. According to the CDC, some dog worms are zoonotic — they can infect humans. Roundworms and hookworms are the main concern. People, especially young children, can pick them up by contacting soil or surfaces contaminated with infected dog feces and then touching their mouths.
- Roundworm larvae in people can, in rare cases, migrate through tissues and even affect the eyes (a condition called ocular larva migrans).
- Hookworm larvae can penetrate human skin and cause an itchy, winding rash (cutaneous larva migrans).
You don’t need to panic, but you should respect basic hygiene:
- Wash hands after handling your dog, picking up stool, or gardening.
- Pick up dog feces promptly from your yard and on walks.
- Keep children’s sandboxes covered and supervise hand-washing.
- Keep your dog on routine deworming and year-round parasite prevention — protecting your dog protects your family.
Prevention: the simple routine
Worm control isn’t complicated when it’s built into a regular routine:
- Deworm puppies on schedule. CAPC recommends starting deworming in the first few weeks of life and repeating it on a defined schedule. If you’re raising a new pup, fold this into your broader plan — our new puppy checklist covers the first vet visits where this gets handled.
- Use year-round broad-spectrum prevention. Many monthly products prevent heartworm and control common intestinal worms at the same time. Your vet will match the product to your dog and region.
- Keep fleas under control. Since fleas transmit the most common tapeworm, consistent flea prevention closes that door.
- Test regularly. Fecal tests at the intervals your vet recommends catch infections you can’t see.
- Clean up stool promptly in your yard and on walks to reduce environmental contamination — for your dog, other dogs, and people.
When to call your vet
Book a visit if you notice visible worms or rice-like segments, ongoing diarrhea or vomiting, a swollen belly, unexplained weight loss, scooting, or a cough and fatigue in a dog that isn’t on heartworm prevention. Puppies, senior dogs, and any dog that seems weak or is passing blood should be seen sooner rather than later.
Worms are common, treatable, and largely preventable. The two habits that matter most are simple: let your vet identify and treat the specific worm rather than guessing, and keep your dog on year-round prevention. Do those two things, and you protect your dog — and everyone who shares a home with them.
This guide is educational and not a substitute for veterinary care. Deworming medication, dosing, and parasite prevention should be directed by your veterinarian. Sources: Companion Animal Parasite Council (CAPC), Merck Veterinary Manual, and the U.S. Centers for Disease Control and Prevention (CDC).