Fleas – how to evict these itchy, uninvited guests

How can you tell if your pet has fleas? What do fleas look like? Why do fleas love our cosy homes so much? Can fleas live on humans? What’s the difference between dog fleas and cat fleas? How long do fleas live? How serious a health risk are fleas? And, most importantly, what do you have to do to get
Featured image for Fleas – how to evict these itchy, uninvited guests
11th March 2021

How can you tell if your pet has fleas? What do fleas look like? Why do fleas love our cosy homes so much? Can fleas live on humans? What’s the difference between dog fleas and cat fleas? How long do fleas live? How serious a health risk are fleas? And, most importantly, what do you have to do to get rid of fleas?

Fleas may not be something you think much about – until you discover your pet has got them. Then you’ll find that these miniscule blood-sucking parasites will be constantly on your mind...

Fleas on dogs and fleas on cats means fleas in the house

If you discover that your pet has got fleas then it’s a pretty safe bet that your home has also become a hangout for these irritating, unwelcome visitors. Fleas are not shy about making an entrance and will happily jump aboard any passing furry animal – or human – to gain access to your humble abode. Once in, they’ll start to colonise, nesting in your soft furnishings, carpets and bedding. So, not only will you have to treat your pet, but you’ll also have to de-flea your home too.


A female flea can feed on up to 15 times her own body weight in blood from her host every day.

Surprisingly, adult fleas generally make up just 5% of a potential infestation. The other 95% consists of flea eggs, larvae and pupae, which are invisible to the naked eye and live in the environment – on beds, rugs, carpets and sofas – not on your pet. That’s why, it’s only by breaking the flea life cycle that you can stop a flea invasion on your property.


The average female flea will lay up to 40 to 50 eggs per day – that’s up to 2,000 eggs during her lifetime!

The ideal temperature for fleas is between 21°C and 29°C. And so, as far as these blood-sucking parasites are concerned, what’s not to love about our cosy, centrally heated homes? Human houses are, quite literally, the perfect breeding ground. This is down to the way a flea life stage develops – from egg to larva, pupa and finally adult.

Fleas have honed their development phase to a fine art and will remain in the pupae stage for up to a year until environmental factors – such as heat and carbon dioxide – indicate that conditions are just right to emerge as a fully-fledged adult flea.


While fleas may bite a human, they don’t like to live on us and will seek out a dog or cat as their preferred host. The two most common species that live and dine on cats and dogs are ‘Ctenocephalides felis’ – the scientific name for cat fleas – and ‘Ctenocephalides canis’ – the scientific name for dog fleas, although cat fleas are not that fussy and will happily live on either cats or dogs.

The lifecycle of a flea

Online animal health magazine My Pet and I outlines the fascinating (and rather gruesome) lifecycle of a flea – there’s even a video that shows what adult fleas, eggs and larvae look like, if you can bear to watch it...

Stage 1: Flea eggs

Once an adult female flea has found a host and eaten a blood meal, she can then reproduce and begin to lay eggs. The eggs are tiny white objects, usually around 0.5mm in size, which is smaller than a grain of sand. It makes it almost impossible to see them, particularly if they’re scattered around your house in the carpet and on the sofa. Female fleas usually lay on average 20 eggs per day but they can lay as many as 50. Flea eggs represent around half the entire flea population in the home. Your dog or cat will then unwittingly distribute the eggs on the flea’s behalf, as they fall off your pet when they move around the home and in the surrounding environment. When the temperature and humidity is right, the eggs will hatch and larvae emerge.

Stage 2: Flea larvae

Flea larvae instinctively avoid direct sunlight because they’re negatively phototactic (they move away from light) and so bury themselves deep into materials and fabrics. Because they can’t yet feed on a host, they survive by eating flea dirt from the environment, the name given to adult flea faeces. Essentially, flea dirt is dried blood and looks like a trail of black specks. Flea larvae are a white, almost see-through colour and have no legs. They develop over one to two weeks and are larger than flea eggs, growing up to 5mm long. In a household flea infestation, larvae make up 35% of the total population. They will be found hiding in dark parts of your home, including carpets, under furniture, under skirting boards, and in pet bedding.

Stage 3: Flea pupae

Flea pupae refers to the cocoon stage of the flea cycle and they make up 10% of the home flea population. This is the final stage before it turns into an adult flea, which can take several days or weeks. If conditions aren’t right, the pupae can survive for months and sometimes more than a year. The cocoon protects the pupae while it develops. The sticky outer layer of the cocoon keeps pupae hidden deep in fabrics and carpets. This helps to keep it out of reach of vacuums and helps to protect pupae from chemicals in some household flea removers. Once developed, the adult flea won’t emerge until they sense a potential host nearby. They are clever and will pick up on vibrations, rising levels of carbon dioxide and body heat, indicating that your dog or cat is nearby.

Stage 4: Flea adults

When an adult flea emerges from the cocoon, they will seek a host to feed on, usually within a few hours. If fleas can’t find a pet (and in some cases, a person) to feed on, they won’t survive. Female fleas can only reproduce once they’ve fed and they’ll begin laying eggs within a few days. Adult fleas change in appearance once they’ve eaten too. A newly emerged adult flea is very small, has a flat-bodied appearance and they’re dark in colour. When the bloodsucking creatures have had their fill, they grow into a recognisable flea shape and take on a lighter shade. They account for 5% of a home flea infestation and are usually found on your pet where they can continue the cycle of feeding and laying eggs for a number of weeks.


The average flea is just 2-3 mm in length and weighs less than 1 gram. However, they can potentially pull up to 160,000 times their own body weight – the same as a human pulling over 2,600 double decker buses.

Why fleas are a serious health risk

Fleas are not just a nuisance, they’re also a serious health risk. Some pets with fleas can develop Flea Allergy Dermatitis (FAD) – an allergic reaction to flea saliva, which can lead to hair loss. Flea infestations can cause anaemia, due to the amount of blood an animal can lose, which in the worst cases can be fatal – especially in young or frail pets. Flea larvae can also become infected with tapeworm eggs. If your pet eats an infected flea when grooming, they can then become a host to this loathsome internal parasite. So, if your pet has fleas you should make sure they are treated for worms too. Fleas can also pass on other nasties, such as myxomatosis, which is a serious disease in rabbits. That’s why it’s essential to take action.


Fleas don’t have wings and instead jump onto their host. Despite their minute size, it’s been suggested that fleas can jump up to 200 times their length and up to 150 times their height. They’re also impossible to crush due to their hard outer casing.

How to tell if your pet has fleas

  • Is your pet scratching?
  • Are there areas of hair loss, bald or sore patches?
  • Spots or scans
  • Redness and irritation?
  • Thickened skin in areas (such as around ear edges)?
  • Can you see tiny dark specks in your pet’s fur, or small browny-black insects scurrying about?
  • Do you have any insect bites yourself?

The RSPCA suggests grooming your pet with a fine-tooth comb held over a white surface - any fleas or droppings will be deposited on the surface. Add a few drops of water and if the droppings turn reddish brown it's very likely your pet has fleas.

Treating your pets – why it’s essential to seek advice from your vet

When it comes to fleas, prevention is always better than cure, which is why it’s essential to keep your pets up to date with their parasite prevention medication. However, if you spot the signs of a flea infestation, seek treatment as soon as possible. Although there are over the counter solutions, from spot-on treatments to tablets, powders, collars and shampoos, it’s always best to seek expert advice from your vet.

NEVER USE A FLEA TREATMENT FOR DOGS ON YOUR CAT. Many flea treatments for dogs contain permethrin. This chemical can be fatal to cats. Make sure you use a flea treatment specifically for cats and check all household flea sprays for permethrin before you use them around your cat.

Burgess in-house vet Dr Suzanne Moyes says: “Dogs, cats, rabbits and other small furries can all suffer from fleas. So, if you’ve identified fleas on one of your pets, all the animals in your home will need treatment – but only with medication that is suitable for their species. This is absolutely vital. Products that are safe for one type of animal may not be suitable for another. For example, dog flea treatments contain permethrin, an insecticide that is safe to use in small doses on canines but is fatal to felines. If you have a multiple pet family, your vet can advise of the best treatment – a cat can die simply by coming in contact with a dog that’s been treated with permethrin. Likewise, if your pet is very young or old, or has any underlying health issues, your vet can suggest the best approach, recommend the right dose according to age and weight and show you the correct way to apply medication.”

How to de-flea your home

As well as treating your pets, you’ll need to give your whole house a clean sweep because both people and pets unwittingly move eggs, larvae and pupae all around your home. When cleaning, pay particular attention to fabrics, carpets and soft furnishings where adult fleas and the younger flea life-stages can lurk...

My Pet and I suggests these great flea-busting tips:

  • Vacuum your house frequently for a number of weeks to ensure you capture as many eggs and larvae as possible. Remember to focus on the areas under furniture where larvae like to hang out. Empty your vacuum cleaner after every clean so they don’t have a chance to re-infest your house.
  • Wash your pet’s bedding and toys in hot soapy water to remove and kill eggs, larvae and pupae. Remember to wash your own bedding on a hot wash too. Curtains shouldn’t be ignored either.
  • Use special home flea spray, which stops the development of flea eggs and larvae and kills adult fleas in those hard-to-reach areas, such as in cracks in the floor and skirting boards and on furniture. 
  • De-flea your car too (and pet carriers). If your pet spends time in your car, they may have spread flea eggs there. If this is the case and the eggs are not dealt with swiftly, they can easily lead to re-infestation of your home.

If you found this interesting, you may also like:

VACCINATIONS – VITAL FOR US AND OUR PETS Find out how vaccinations work, what dog vaccinations, cat vaccinations, rabbit vaccinations and ferret vaccinations protect against, when your pets should be vaccinated and lots more essential information...

PROTECT AND PREVENT Raising awareness of the deadly Rabbit Viral Haemorrhagic Disease 2 (RVHD2) and asking all rabbit owners to make sure their pets are vaccinated against this and other fatal diseases.

HOW TO PROTECT YOUR GUINEAS AND BUNNIES FROM PESKY PARASITES When it comes to protecting our gorgeous small pets from mites, fleas, flies, ticks and mosquitoes – and any other irritating and unwelcome pests – a four-pronged attack is the best approach.

THE DANGER OF DIAGNOSING YOUR PET'S PROBLEMS ONLINE Our in-house vet Dr Suzanne Moyes explains why, if you’re worried about your pet’s health, you should always seek advice from your veterinary surgeon, rather than a search engine.

NEUTERING – ONE OF THOSE THINGS ON YOUR 'TO DO' LIST? Is neutering your pet one of those things you’ve thought about but just haven’t got around to? Our in-house vet Dr Suzanne Moyes explains why neutering is one of the best things you can do for your pet

CATS AND THE BENEFITS OF NEUTERING Neutering is a simple operation that will not only stop unwanted pregnancies, but also benefit your cat’s overall health and wellbeing.

KEEP CALM AND CALL THE VET If your much-loved pet suddenly became unwell or suffered an injury, would you know what to do? What symptoms should you look out for that suggest the situation is serious? When should you call the vet? 

Sources: mypetandi.com , rspca.org.uk , animeddirect.co.uk , pdsa.org.uk

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