Search for the most aggressive dog breeds and you will find list after list, all confident, most of them naming the same half dozen dogs. Search for the best family breed and you get the same thing in reverse.

The largest study ever done on dog behaviour looked at this directly, and the answer it came back with is awkward for every one of those lists: breed tells you far less about an individual dog than people assume.

What the biggest study actually found

In 2022 a team published a paper in Science called “Ancestry inclusive dog genomics challenges popular breed stereotypes”. They surveyed the owners of 18,385 dogs, purebred and mixed, and genotyped 2,155 of them.

The headline number: breed accounts for roughly 9% of the behavioural variation between individual dogs.

Nine percent. Which means that if you line up a hundred dogs and ask why one is bolder, calmer or more easily startled than another, breed explains about a tenth of the answer. Everything else is the individual animal, how it was raised, what happened to it, and chance.

Worth being precise, because a lot of the coverage of this paper overstated it. The study did not find that genetics is irrelevant. Most of the behavioural traits it measured were meaningfully heritable, with heritability above 25%. Genes matter. What the study undercuts is the breed label as a shortcut for predicting an individual dog.

The part that matters for the aggression lists

The researchers broke behaviour into separate factors rather than treating it as one lump, and breed predicted some far better than others.

Biddability, meaning how readily a dog responds to human direction, was one of the better ones. Knowing a dog’s breed ancestry does make that somewhat more predictable, which will surprise nobody who has met a Border Collie.

And then there is agonistic threshold: how easily a dog is provoked, by a stranger, a noise, a sudden approach. This is the trait sitting underneath every aggressive breeds list ever written.

For that trait, breed was nearly uninformative.

That is the finding worth sitting with. The single behaviour those lists exist to predict is the one breed predicted worst.

Why breeds look so different but behave so similarly

It seems contradictory. A Chihuahua and a Great Dane could not look less alike, so why would their behaviour not differ just as sharply?

The authors’ answer is about timing. The behaviours we think of as doglike, the herding, the retrieving, the guarding, came from thousands of years of selection that happened before modern breeds existed. Breeds as we know them are mostly a Victorian invention, a couple of hundred years old, and what they were selected for hardest was appearance.

So we spent two centuries breeding dogs to look distinctive and comparatively little time breeding them to behave distinctively. The visible differences are dramatic and recent. The behavioural ones are older, shared, and spread across all of them.

What this does not mean

This is where it would be easy to overcorrect, so three things the study does not say.

It does not say all dogs are the same. Dogs differ enormously. It says breed is a weak guide to which dog is which.

It does not say size and strength do not matter. Breed predicts physical capability very well indeed, and that is not a behavioural question. A frightened Chihuahua and a frightened mastiff may be equally likely to bite. They are not equally capable of causing harm, and anyone choosing a dog should think honestly about that.

It does not say breed is useless. Coat type, exercise need, grooming, likely size, common health problems, these are all far more predictable from breed than temperament is. If you want to know whether a dog will need two hours of exercise a day or shed on everything you own, breed is genuinely informative.

So how should you actually choose a dog?

Use breed for the things it predicts well, and meet the individual for the things it does not.

• Use breed to predict the practical stuff. Adult size, coat and grooming, exercise needs, and the health problems that run in that line. Ask a breeder directly what the line is screened for.
• Meet the actual dog, more than once if you can. For temperament, ten minutes with the animal in front of you beats any amount of reading about its breed.
• Ask about the parents and the early weeks. Early socialisation between roughly three and sixteen weeks shapes an enormous amount, and it is already happening before you collect a puppy.
• Be honest about strength, not just temperament. Match the dog’s physical capability to who lives in your house and who will be holding the lead.
• Do not rule out a mixed breed on predictability grounds. The study’s whole point is that purebred does not buy you nearly as much behavioural certainty as the price tag implies.

A note on the limits of this research

It would be inconsistent to use one study to knock down the breed lists and then treat that study as beyond question, so here are its weaknesses.

The behavioural data came from owner surveys, not from researchers observing dogs directly. Owners are not neutral about their own dogs, and someone who bought a breed because of its reputation may unconsciously report behaviour that fits. The genotyped sample, 2,155 dogs, is large for this kind of work but small against the world’s dog population. And 9% is an average across the whole dataset, which means some traits and some breeds sit above it.

None of that overturns the finding. It does mean the honest summary is “breed is a much weaker predictor than the lists claim”, not “breed means nothing”.

Frequently asked questions

Which dog breed is the most aggressive?

The research does not support naming one. In the largest study of dog behaviour to date, agonistic threshold, the trait that captures how easily a dog is provoked, was the behaviour breed predicted worst of all. Breeds that appear on these lists tend to be common, large and strong, which affects how much damage a bite does rather than how likely a bite is.

So does breed matter at all?

Yes, for different things than people expect. Breed predicts adult size, coat, grooming, exercise needs and inherited health problems well. It predicts temperament poorly. Use it for the first list and meet the individual dog for the second.

Are mixed breed dogs less predictable than purebreds?

Less than you would think. Since breed explains only around 9% of behavioural variation between individuals, the certainty a pedigree appears to offer about temperament is mostly illusory. Mixes are less predictable in appearance and adult size.

What is the best dog breed for a family?

There is no breed answer to that, which is why every list disagrees. The useful questions are practical: how much exercise can you genuinely commit to, how much grooming and shedding will you tolerate, how big a dog can everyone in the house physically manage, and what does this particular dog seem like when you meet it.

If breed is a weak predictor, why do Border Collies all seem to herd?

Because some traits do track breed better than others. Biddability, how readily a dog takes direction from a person, was one of the better predicted traits in the study. It is the easily provoked end of behaviour where breed stops being informative.

The honest summary

Breed is a good guide to what a dog will look like, how big it will get, how much it will shed and what it might need treating for. It is a poor guide to who that dog will be.

The most aggressive breeds lists are built on the one trait the evidence says breed predicts worst. Read them accordingly, and judge the dog in front of you instead.

This article is general information and is not a substitute for veterinary or professional behavioural advice. If your dog is showing aggression, speak to your vet, who can rule out pain and refer you to a qualified behaviourist.

Source: Morrill K. and colleagues, “Ancestry inclusive dog genomics challenges popular breed stereotypes”, Science, 2022, volume 376, article eabk0639.

You are stroking your cat and your hand stops on a lump. It is firm, about the size of a grape, and when you part the fur there is a small hole in the middle of it. Something moves.

Your first instinct will be to squeeze. Every botfly removal video on the internet ends with someone squeezing. Please do not, and this article is mostly about why, because that single decision is what separates a minor vet visit from a genuine emergency.

What a botfly actually is

In North America the botfly that turns up on pets is Cuterebra. The adult is a thick, furry fly that looks more like a bumblebee than a housefly, and it does not bite, feed or sting. It has no mouthparts worth speaking of. The adult’s only job is to mate and lay eggs.

Those eggs go near the burrows and runways of rabbits and rodents, on stones, on stems, along the paths those animals use every day. The eggs then sit and wait. They hatch in response to the warmth of a body passing close by.

That is the whole mechanism, and it explains everything else. The fly is not hunting your pet. It is waiting for a cottontail.

The myth: it did not burrow through your pet’s skin

This is the detail almost every article gets wrong, and getting it right changes how you prevent it.

The larva does not land on your dog and drill inward. According to the Merck Veterinary Manual, larvae enter mainly through the mouth or the nostrils while the animal is grooming or sniffing, and less commonly through an existing open wound. Intact skin is not the doorway.

So the lump on your cat’s neck did not start on your cat’s neck. It started at the nose or the mouth, and the larva then travelled through the body before settling under the skin to finish growing.

Which tells you where the risk really is: a pet with their face down a burrow. Cats that hunt, and dogs that push their nose into holes in a hedge bank, are the ones that get this.

What it looks like on a dog or cat

The textbook lesion is a soft, well defined swelling under the skin, roughly one centimetre across, with a small breathing hole in the centre. That hole is not damage. The larva made it deliberately so it can breathe, and it sits with its rear end against the opening.

In practice, here is the order most owners notice things:

• Matted, damp fur over one spot, because the animal has been grooming or licking it obsessively. On cats this is very often the first sign, before anyone finds a lump.
• A lump that feels soft rather than solid.
• A central hole, sometimes oozing, sometimes with something visibly moving in it.
• Late summer and early autumn. This is a seasonal problem and it clusters there.

Lesions sit mostly around the head, neck and trunk. Pain varies, and when it hurts that is usually a secondary bacterial infection rather than the larva itself.

Worth knowing: the most common thing this gets mistaken for is an abscess or a foreign body, which is reasonable, because that is exactly what it looks like. If your vet finds a larva in it, the diagnosis is settled on the spot.

Why you must not squeeze it

Here is the part that matters.

A mature Cuterebra larva is a fat, stiff, barrel shaped thing covered in rows of dark spines. It is not a maggot you can flick out. It is firmly anchored in a pocket under the skin, and it is wider than the hole it breathes through.

Squeeze it and one of two things happens. Either it holds, and you achieve nothing but pain. Or it ruptures.

Rupturing it is the problem:

• Chronic foreign body reaction. Merck is explicit that squeezing can rupture the larva and cause a chronic foreign body reaction and secondary infection. Spines and fragments left in the tissue keep the wound angry for months.
• Recurrent abscesses. If a lump keeps coming back at a spot that was treated before, that points at larval remnants still in there.
• Anaphylaxis. There are reports of a ruptured larva triggering a severe allergic reaction. Merck describes these as anecdotal rather than common, so this is not a likely outcome, but it is a dangerous one and the risk is entirely avoidable.

Also, do not try to smother it. Vets do use petroleum jelly over the breathing pore, but only for ten to fifteen minutes immediately before grasping the larva with instruments, as a way to bring it within reach. Covering the hole and walking away kills the larva in place, which leaves you with exactly the decomposing foreign body you were trying to avoid.

And do not cut it out at home. The opening has to be enlarged carefully around a parasite you cannot see the shape of.

What the vet actually does

It is a quick procedure and it is not dramatic.

1. The breathing pore is carefully enlarged so the larva can come out without being compressed.
2. If the larva retreats deeper, which it does, petroleum jelly over the pore for ten to fifteen minutes brings it back up within reach.
3. It is grasped with mosquito forceps and lifted out in one piece. Whole is the whole point.
4. The cavity is flushed with sterile saline and any dead tissue trimmed away.
5. The wound is left to heal from the inside out, which can take weeks to months, so do not expect it to close over in days.

Sedation is often used, mostly so the animal stays still rather than because it is agonising. Antibiotics get added when the site is already infected, which is common, because that breathing hole is an open door for bacteria.

The rare version that is genuinely serious

Dogs, cats and ferrets are all accidental hosts, which means the larva has no reliable map inside them. Usually it ends up under the skin and that is the end of it. Occasionally it goes somewhere it should not.

Aberrant migration is documented into the nasal passages, the pharynx, the eyelids and the brain. The signs depend entirely on where it went:

• Airway. Sneezing, upper respiratory signs, and in the worst case difficulty breathing. A larva in the upper airway is an emergency.
• Brain. Depression, lethargy, seizures, blindness, odd mentation, a temperature that is too high or too low.

There is a history that vets specifically ask about in cats with sudden neurological signs: an episode of violent sneezing weeks to months earlier. That is the larva going up the nose. Central nervous system cases cluster between July and September.

Veterinary pathologists and neurologists at Cornell were the first to propose that feline ischemic encephalopathy, a stroke like brain condition in cats, is caused by this migration. The evidence is case series and pathology reviews rather than a controlled study, and the link is considered likely rather than proven, so treat it as a strong suspicion. The supporting pattern is hard to ignore though: where Cuterebra species do not live, the condition is not reported, and the seasons line up.

One breed note. Merck flags Yorkshire Terriers as possibly at increased risk, and able to mount a severe whole body inflammatory response.

None of this is common. The point is simply that “it is only a lump” is the wrong frame if your pet also has neurological or breathing signs.

When to get to a vet urgently

• Any difficulty breathing, or noisy, laboured breathing
• Seizures, collapse, circling, sudden blindness or disorientation
• Sudden unexplained lethargy in a cat that was outdoors in late summer
• A lump that bursts, bleeds heavily or spreads redness and heat across the surrounding skin
• Anything that follows an attempt to squeeze it out at home

Prevention, such as it is

There is no vaccine and no monthly preventive marketed for this, so prevention is behavioural.

• Cut unsupervised outdoor time in late summer and early autumn, which is when infestation peaks.
• Know where the burrows are. If there are rabbit or rodent holes in your garden or on your usual walk, that is the hazard. Blocking access to them does more than anything else.
• Check your pet over after they have been out, the same habit that catches ticks early. Run your hands over the head, neck and body, and pay attention to any patch of fur that is suddenly damp or matted.
• Indoor cats essentially do not get this. Free roaming cats are the ones at risk, and botflies are only one item on a long list of reasons outdoor access costs cats years. We compare the two directly in how long do cats live, indoor versus outdoor.

Obsessive licking at one spot has a long list of possible causes, and most of them are not parasites. We go through them in why is my dog scratching so much.

If what you are looking at is a wound full of small, soft, pale maggots rather than a single large larva in a neat hole, that is a different problem with different urgency, and it is covered in our guide to screwworm in dogs and cats.

Frequently asked questions

Can I pull a botfly out of my dog myself with tweezers?

No. A mature larva is wider than the hole it breathes through and it is anchored in a pocket under the skin, so pulling tends to tear it rather than remove it. A ruptured larva can cause a chronic foreign body reaction, recurrent abscesses and, rarely, a severe allergic reaction. The opening needs enlarging first, which is a vet job.

Can my dog catch a botfly from my cat, or can I catch it?

No. There is no animal to animal or animal to human spread. Every infestation comes from a larva picked up in the environment near rabbit or rodent burrows, so two pets in the same household can both get one from the same garden without either giving it to the other.

What happens if I just leave it alone?

The larva will eventually finish developing and leave on its own to pupate in the soil. The reasons not to wait are that the open breathing hole frequently becomes infected, the animal often traumatises the area by over grooming, and you have no way of knowing whether a second larva went somewhere more dangerous.

Is a botfly lump the same as an abscess?

They look very similar, and an abscess or foreign body is the most common misdiagnosis. The distinguishing feature is the small central breathing pore, and the diagnosis is confirmed by actually finding a larva. If a lump at a previously treated site keeps recurring, that can mean larval fragments were left behind.

Do indoor cats get botflies?

Essentially no. The larva has to be picked up outdoors, near the burrows and runways of rabbits and rodents. Free roaming cats are far more likely to be affected than indoor cats.

Does my pet need treatment if the larva has already gone?

Get the site checked. An empty cavity still needs flushing and often needs antibiotics, because the hole has been open to the environment for weeks. Your vet will also want to be sure nothing was left behind.

The honest summary

A lump with a breathing hole in it, on a dog or cat, in late summer, after time spent outdoors, is very likely a Cuterebra larva. It got in through the nose or the mouth, not through the skin.

Do not squeeze it. Do not smother it and leave it. Do not cut it out. All three carry a real risk of rupturing the larva, and a ruptured larva turns a fifteen minute procedure into weeks of recurrent infection, with a small chance of something far worse.

Take your pet to the vet, mention the breathing hole, and mention anything odd in the preceding weeks, especially a fit of violent sneezing. It is a small problem handled properly and a genuinely nasty one handled with your fingers.

This article is general information and is not a substitute for veterinary advice. If your pet is unwell, contact your vet.

Sources: Merck Veterinary Manual, Cuterebra infestation in dogs and cats; MSD Veterinary Manual, Cuterebra infestation in small animals; Glass and colleagues, Cuterebra myiasis of the central nervous system in cats, 1998; Williams, Summers and de Lahunta, cerebrospinal cuterebriasis and its relationship to feline ischemic encephalopathy, Veterinary Pathology, 1998; University of Guelph Animal Health Laboratory, feline cerebral cuterebriasis.

You part your dog’s fur and there it is: a grey or brown lump, legs buried in the skin. The urge is to grab it and pull, or to reach for whatever the internet told you about petroleum jelly. Both instincts can make it worse.

Removing a tick properly takes about thirty seconds and one tool. The part almost nobody gets right is what happens afterwards, because the single most repeated piece of tick advice, that you are safe if you remove it within twenty four hours, is only true for one disease.

How to remove a tick from a dog

This is the method the US Centers for Disease Control and Prevention gives, and it is the same technique vets use.

1. Use fine tipped tweezers. Grasp the tick as close to the skin’s surface as possible, so you are holding its head and not its body. If you have no tweezers, fingers will do, but do not squeeze the body.
2. Pull straight up with steady, even pressure. Do not twist. Do not jerk. Twisting or jerking is what breaks the mouthparts off in the skin.
3. Clean the bite and your hands with rubbing alcohol, or soap and water.
4. Dispose of the tick without crushing it. Never crush a tick between your fingers. Put it in alcohol, seal it in a bag, wrap it in tape, or flush it.
5. Write down the date. This matters more than people expect. If your dog becomes unwell weeks later, the date of a tick bite is the single most useful thing you can tell your vet.

What not to do, and why it actively increases the risk

The folk remedies all share one idea: irritate the tick until it backs out on its own. The CDC warns specifically against painting the tick with nail polish or petroleum jelly, and against using heat to make it detach.

The reason is not squeamishness. A distressed tick is a dangerous tick. In the CDC’s words, these methods may agitate the tick and force infected fluid from the tick into the skin. You are asking an animal whose gut may contain bacteria to vomit into the bite it has already made.

So, the list of things not to do:

• No petroleum jelly, nail polish or soap smothering.
• No burning, no matches, no lighters, no hot needles.
• No twisting or unscrewing. Ticks do not thread into the skin, so there is nothing to unscrew. Twisting only snaps the mouthparts.
• No waiting for it to let go. The CDC is explicit that you remove it promptly rather than waiting for it to detach. Every extra hour matters, for reasons below.
• No crushing it with your fingers.

You left the head in. Is that an emergency?

No, and the worry is out of proportion to the risk.

If the mouthparts break off, the CDC’s guidance is to try to remove them with clean tweezers, and then this: if you are unable to remove the mouth easily with clean tweezers, leave it alone and let the skin heal.

Left behind mouthparts cannot transmit disease. There is no tick still feeding, because the tick is gone and what remains is an inert fragment. The body treats it like a splinter and pushes it out. Digging at it with a needle causes far more damage than leaving it, and risks a skin infection that the tick itself was never going to cause.

Watch the spot for a few days. A small bump at a bite site is normal and can persist for a week or two. Spreading redness, heat, swelling or pus is a vet visit, but that is a skin infection from the wound, not tick borne disease.

Why the twenty four hour rule is wrong

This is the part worth reading twice, because it is the opposite of what most articles tell you.

The advice that a tick must be attached for twenty four hours before it can transmit anything comes from Lyme disease, and for Lyme it is broadly right. The Merck Veterinary Manual puts transmission at a minimum of twenty four hours of attachment, usually thirty six to forty eight hours into the blood meal. The risk climbs with time rather than switching on: roughly 10% by forty eight hours from a single infected nymph, around 50% by sixty three to sixty seven hours, 70% by seventy two hours.

Lyme is not the only thing ticks carry, and the others are much faster.

• Ehrlichia, which causes ehrlichiosis in dogs, can be transmitted within three to six hours of attachment, according to the Companion Animal Parasite Council.
• Rocky Mountain spotted fever is generally thought to transmit five to twenty hours after attachment.
• Anaplasma sits somewhere in between, and the research genuinely disagrees, with some experimental transmission reported inside the first twenty four hours.

So “I found it the same day, we are fine” is false comfort. For the fastest of these, a tick attached over a single night has already had time. CAPC’s own wording is that attached ticks should be removed promptly to prevent transmission of any pathogens they may harbor. Promptly means now, not within a day.

This does not mean panic. It means two things. Remove ticks the moment you find them rather than finishing the walk first. And do not use the twenty four hour rule to decide whether a bite was harmless.

What to watch for afterwards

Most tick bites cause nothing at all. If something does develop, it is usually one to three weeks later, which is why that date you wrote down matters.

• Lethargy and a dog that is simply not themselves
• Fever, loss of appetite
• Lameness that moves from one leg to another, which is a classic Lyme sign in dogs
• Swollen joints or obvious pain on being touched
• Pale gums, bruising or nosebleeds, which can point at a platelet problem from ehrlichiosis or anaplasmosis

Dogs do not get the expanding bullseye rash that people do, so do not wait for a skin sign. Tell the vet there was a tick and when.

Where ticks hide on a dog

Run your hands over the whole dog after walks, and check the places ticks prefer: inside and around the ears, under the collar, in the armpits and groin, between the toes, under the tail, and around the eyelids. On a thick coated dog you will feel a tick before you see it.

Persistent scratching is not a reliable tick sign, and it has a long list of other causes, which we go through in why is my dog scratching so much.

Prevention beats removal

CAPC recommends that all dogs be kept on tick control products year round, not seasonally. Ticks are active whenever it is above freezing, and a mild winter week is enough.

Because some of these pathogens transmit within hours, the maths favours products that kill or repel ticks quickly over relying on you finding every tick in time. A product that kills a tick before it has fed for six hours is doing something your daily check cannot reliably do.

Ticks are not the only parasite worth a routine check. Fleas carry tapeworm, so the three problems travel together more often than owners expect, and our guide to worms in dogs and cats covers what a stool test can and cannot tell you.

Ticks and fleas are different problems needing different products, and a flea treatment does not necessarily cover ticks. If you are dealing with both, our step by step flea guide covers the part people miss, which is that most of the flea population is in your house rather than on your dog.

Frequently asked questions

Do I need to send the tick for testing?

Usually no. A tick testing positive does not mean your dog was infected, and a negative result does not rule it out, because your dog may have had another bite you never found. Treatment decisions are made on your dog’s symptoms and blood tests, not on the tick. Keeping the tick in a sealed container is still useful for identification if your vet wants to know the species.

Should my dog have antibiotics straight away after a tick bite?

Generally not. Most bites transmit nothing, and treating every bite would mean a great deal of unnecessary antibiotics. Vets normally watch and test rather than treat blind. That is your vet’s call, and it is a conversation worth having if you live somewhere with high tick numbers.

Can I use a tick hook or tick twister instead of tweezers?

Yes. Purpose made tick removers work well and many vets prefer them, especially on small ticks. Follow the instructions that come with the tool, and whatever you use, the principle is the same: grip at the skin, lift the tick away, do not squeeze its body.

Can my dog give me a tick borne disease?

Not directly. Your dog cannot pass Lyme or ehrlichiosis to you. What a dog can do is carry an unattached tick indoors, which then finds you. That is a real route, and it is another argument for year round tick control on the animal.

Do ticks die in winter?

No. They become inactive in hard cold and then resume whenever the temperature rises above freezing. This is why CAPC recommends year round prevention rather than a tick season.

The honest summary

Fine tipped tweezers, grip at the skin, pull straight up, do not twist. No jelly, no flame, no nail polish, because those make the tick regurgitate into the bite. A broken off mouthpart is a splinter, not an emergency.

And the twenty four hour rule is a Lyme rule. Ehrlichia needs three to six hours. Remove ticks the moment you find them, keep the dog on year round prevention, write down the date, and tell your vet about the bite if your dog goes off colour in the following weeks.

If your dog is lethargic, lame in a leg that keeps changing, or off their food in the weeks after a tick bite, that is a vet visit, not a wait and see.

This article is general information and is not a substitute for veterinary advice. If your pet is unwell, contact your vet.

Sources: US Centers for Disease Control and Prevention, tick removal and what to do after a tick bite; Companion Animal Parasite Council, Ehrlichia and Anaplasma guidelines and Rocky Mountain spotted fever guidelines; Merck Veterinary Manual, Lyme borreliosis in animals; Cornell University Riney Canine Health Center, Lyme disease.

Most owners meet worms the same way: something that looks like a grain of rice, moving, near the dog’s tail. It is a horrible moment, and the internet’s answer is usually a product link. This guide does the part that gets skipped. What the five worms actually are, what you can and cannot see, which ones can infect you, and why a clear test result does not always mean a clear dog.

Worms in dogs and cats are common, treatable, and mostly preventable. The complication is that the signs overlap with a dozen harmless things, and the most recognisable worm is the one a lab test is most likely to miss.

The five worms worth knowing

Four live in the intestine. The fifth lives in the heart and lungs and is a different problem entirely.

Roundworms are the ones most people picture: long, pale, spaghetti like. Pets pick up the eggs from contaminated soil or faeces. In puppies and kittens they cause the classic pot bellied look, poor growth and digestive upset.

Hookworms are small and bite into the intestinal wall to feed on blood. Larvae get in by mouth or straight through the skin, often the feet. They cause anaemia, skin irritation and, in young animals, serious illness. The Companion Animal Parasite Council calls hookworms one of the most significant intestinal parasites of dogs.

Whipworms live in the large intestine and cause chronic watery or bloody diarrhoea and weight loss. They mostly affect adults rather than puppies.

Tapeworms are flat and segmented, and they are the ones you are most likely to see with your own eyes. More on these below, because they behave differently from the rest.

Heartworm is not an intestinal worm at all. It is carried by mosquitoes, lives in the heart and pulmonary arteries, and causes coughing, exercise intolerance and eventually heart failure. Deworming tablets do nothing for it. It needs its own monthly preventive and its own blood test.

Tapeworm is a flea problem in disguise

This is the single most useful thing in this article, and it is the part that almost never gets said plainly.

The common tapeworm of dogs and cats is Dipylidium caninum, and animals do not catch it from other animals, or from soil, or from each other. They catch it by swallowing an infected flea, usually while grooming. Cornell’s Riney Canine Health Center is explicit that reinfection happens if the source, meaning fleas or rodents, is not dealt with.

So if you find rice grain segments, you have learned two things, not one. Your pet has a tapeworm, and your pet has or recently had fleas. Treat only the worm and it comes back, because the actual supply line is untouched. Our step by step flea guide covers the part that matters, which is the 95% of the flea population living in your carpets rather than on your dog.

The second tapeworm, Taenia, comes from eating rodents. Same logic. The worm is a symptom of the hunting.

What you can actually see

Honest answer: usually very little, and almost never the worm itself.

• Rice grain segments near the anus, in the bedding, or on the stool. Fresh ones move. Dried ones look like sesame seeds. This is tapeworm, and it is the one clear visual sign.
• Scooting, dragging the rear along the floor. Often blamed on worms, and tapeworm segments genuinely do cause it, but full anal glands cause it far more often. Persistent itching and scratching has its own long list of causes, most of them not worms at all, which we go through in why is my dog scratching so much.
• A pot bellied puppy with a dull coat and poor growth, which points at roundworms.
• Chronic diarrhoea, sometimes bloody, which points at whipworms.
• Pale gums and lethargy, which can mean hookworm anaemia and needs a vet quickly in a puppy or kitten.
• Nothing at all. Plenty of infected adult animals look completely well. This is the normal case, not the exception.

Why a clear test does not always mean a clear pet

Diagnosis is usually a faecal flotation, where a stool sample is spun or floated so that any eggs rise and can be counted under a microscope. It works well for roundworm, hookworm and whipworm.

It is unreliable for tapeworm. Cornell notes that faecal testing may find tapeworm eggs but can often miss an active infection. The reason is mechanical: tapeworms shed whole segments containing egg packets rather than releasing loose eggs steadily into the stool, so a given sample may contain none at all.

The practical consequence is worth stating clearly. If you saw rice grain segments, tell your vet you saw them, even if the lab result came back negative. What you saw is better evidence than the test, and treatment is usually given on that basis.

Worms are seasonal, and not in the direction you would guess

Most people assume parasites are a summer problem. Research on US fecal data found that prevalence of both whipworm and roundworm peaked in winter, while hookworm peaked in late summer and early autumn.

Year round prevention exists for this reason. Stopping in October because the weather turned is stopping at the wrong moment for two of the four.

Can you catch worms from your pet

Yes, for some of them, and this is the part worth taking seriously without panicking about it.

Roundworm. The CDC describes toxocariasis as an infection caught from Toxocara, spreading to people from animals, usually dogs or cats. Eggs in animal faeces reach people’s mouths through contaminated dirt or unwashed hands. It does not spread person to person. Young children are at the highest risk, particularly those playing in or eating contaminated soil. In its ocular form it can damage the retina and cost vision, usually in one eye. In its visceral form it moves into organs such as the liver or the central nervous system.

Hookworm. CAPC describes dog hookworms as the most common cause of cutaneous larva migrans in people, where larvae burrow through skin and leave intensely itchy winding tracks. Gardeners, outdoor workers and people who walk barefoot on contaminated sand or soil are the usual cases.

Tapeworm. Human infection with the flea tapeworm is rare, and it requires swallowing an infected flea, which is why the handful of reported cases are mostly in young children.

None of this is a reason to rehome a pet. It is a reason to pick up faeces promptly, wash hands after the garden, keep sandpits covered and keep the dog wormed.

What to actually do

1. Do not guess the worm. Different worms need different drugs. The praziquantel that clears a tapeworm does nothing useful against whipworm, and a general wormer may not cover tapeworm at all. Identify first.
2. Take a stool sample to your vet, and mention anything you saw with your own eyes.
3. Expect the right drug, not the strongest one. Tapeworm is treated with praziquantel, which works quickly, often within a day.
4. Deal with the source. For tapeworm that means fleas, every animal in the house, and the house itself. Skipping this guarantees a repeat.
5. Keep heartworm separate in your head. It is a different parasite with a different route and a different medicine.

How often should pets be tested

CAPC recommends testing for intestinal parasites at least four times in the first year of life, and at least twice a year in adults depending on the animal’s health and lifestyle.

For puppies the schedule starts earlier than most owners expect. CAPC advises treating puppies and their mothers when the young are two, four, six and eight weeks old, then moving on to monthly preventives as soon as the product label allows. The reason is blunt: dormant larvae in the mother are so common that essentially every nursing puppy is assumed to be at risk.

What does not work

Eating grass is often read as a sign of worms too. It is not a reliable one, and the reasons dogs do it are covered in why do dogs eat grass.

Garlic, diatomaceous earth, pumpkin seeds, raw carrot and apple cider vinegar are all recommended online as natural wormers. None of them clear an established worm burden, and garlic is toxic to dogs and cats in meaningful amounts. Using them instead of a real wormer means the infection continues, and in a puppy with hookworms that delay matters.

Worming the pet but not the home is the other common miss, and it is the reason the same tapeworm appears to come back a fortnight later.

Frequently asked questions

What do worms in dog poop look like?

Roundworms look like pale spaghetti and are usually only seen after a wormer or in a heavy infection. Tapeworm segments look like moving grains of rice when fresh and sesame seeds when dried, and are more often found on the fur near the anus or in bedding than in the stool itself. Hookworms and whipworms are essentially never visible to the naked eye and are found only on a faecal test.

Can I treat worms without going to the vet?

You can buy wormers over the counter, but you need to know which worm you are treating, because the drugs differ. A product that clears roundworms may do nothing to tapeworms. If your pet is a young puppy or kitten, is losing weight, has bloody diarrhoea or pale gums, see a vet rather than guessing.

My dog has tapeworm but I have never seen a flea. How?

This is the usual situation. A dog only has to swallow one infected flea while grooming, and grooming is also how dogs remove fleas, so the evidence eats itself. Finding tapeworm segments is reliable evidence of flea exposure even when you never saw a flea.

How soon do wormers work?

Praziquantel kills tapeworms quickly, often within about a day, and the worm is digested rather than passed, so you usually see nothing. For other worms you may see dead worms in the stool for a day or two. Not seeing anything does not mean the treatment failed.

Do indoor cats get worms?

Yes. Fleas come indoors on clothing, on other pets and from shared walls in flats, and a single infected flea is enough for tapeworm. Indoor cats that hunt mice in the house can also pick up Taenia.

The honest summary

Four intestinal worms and one heartworm, each with its own route in and its own drug. Most infected animals look fine. The only worm you are likely to see is the tapeworm, and that one is really a flea problem. A negative faecal test rules out a lot, but it does not rule out what you saw with your own eyes.

If your pet is scooting, losing weight, or you have found anything that looks like rice near their back end, book the stool sample and say what you saw.

This article is general information and is not a substitute for veterinary advice. If your pet is unwell, contact your vet.

Sources: Companion Animal Parasite Council hookworm guidelines; US Centers for Disease Control and Prevention, toxocariasis; Cornell University Riney Canine Health Center, tapeworms; American Veterinary Medical Association, intestinal parasites in cats and dogs; VCA Hospitals, internal parasites in dogs.