Latest News

Cat Flea Protection: Starting from Scratch!

Keeping your cats, your family and your home safe from fleas – starting from scratch

Fleas. We all know about them. We all hate them. Our cats certainly hate them. Some of us will start scratching at the mere thought of those jumpy, itch-inducing, disease-ridden pests. But how much do we really understand about fleas, how they reproduce and live, how they affect us and our pets? Most importantly, how well do we understand how to get rid of them – safely - and how to prevent them from coming back?

In order to answer these questions, it is necessary to inflict upon you a brief science lesson, which might seem irrelevant and boring, but bear with me and you will come to understand the meaning of life. The life of a flea.

Introducing the Cat Flea (Ctenocephalides felis) 

There are over 2,000 species of flea, with the species affecting domestic cats aptly referred to as the “cat flea” or Ctenocephalides felis

Ctenocephalides felis (male) - Source: Ken Walker Museums Victoria
The cat flea is also found on dogs and some other mammals, being more versatile with regards to its host than its relation the “dog flea” or Ctenocephalides canis.

Fleas are a type of arthropod, meaning that instead of a spine they have a hard outer skeleton and jointed legs. Fleas are in a category of arthropod known as insects (6 legs). Other types of arthropods include arachnids (spiders) and crustaceans (crabs, lobsters etc.)

Fleas are parasites; a parasite is an organism which lives on/inside a host from which it gets its nutrition, usually with adverse effects on that host. They are an obligate parasite, which means they cannot complete their life cycle without a host, such as a cat or dog. In the case of the cat flea, it needs a blood meal from its host before it can reproduce.

Fleas are classified as ectoparasites (ecto = outer or external), meaning that they live on the outside of their host. Other examples of ectoparasites include ticks, mites and lice. This is in contrast to endoparasites (endo = internal or within), which live inside the host, such as intestinal worms, heartworm and lungworm.

  • Ctenocephalides felis: cat flea
  • Ctenocephalides canis: dog flea
  • Parasite: a living organism which lives inside or on the outer surface of a host and feeds off that host, usually with no benefit to that host
  • Ectoparasite: lives on the outside of the host
  • Endoparasite: lives inside the host
  • Obligate parasite: requires a host in order to complete its life cycle
  • Arthropod: an invertebrate; lacking a spine but has a hard outer skeleton and jointed legs

All you ever wanted to know about Fleas ... and then some!
1. Fleas are 1-2 mm long and are well known for being able to jump great heights and lengths in relation to their body size. While reports of this jumping ability vary widely, they appear to rarely jump higher than human ankle height. This explains why flea bites on humans are often found around the ankles. Fleas also move along their host (e.g. the cat) by jumping; a flea which crawls is likely sick/dying or injured.

2. While fleas can parasitise other hosts, such as humans, we are not their preferred host, and fleas from dogs and cats are unlikely to jump from them onto us

This is because once they find a satisfactory host they will not search for another. This is also the reason why fleas will not usually jump from one cat or dog to another, so it is uncommon for flea transfer between hosts to occur with adult fleas. The most common route of flea transfer between pets is from immature flea stages in shared bedding and sleeping areas.

3. If a host’s body temperature drops, fleas need to find a new host, because without a suitable host to feed off, they will soon die.

4. Only the adult stages of fleas are parasitic.

5. Fleas prefer a warm, humid environment, both in their immature stages of development and when erupting as adults. This is one reason why the advent of warmer weather is often accompanied by a seemingly “new” flea infestation.

6. Fleas cannot drown, because they are not heavy enough to sink below the water’s surface. A flea trapped on water will float until it starves to death.

7. Because cats are such fastidious groomers, many flea eggs laid in their fur are swallowed by the cat during grooming.

Stages of the Flea Life Cycle:

  • Adult: being an obligate parasite, the cat flea needs to feed off a host (your cat) before it is able to reproduce. Once they have jumped onto a host, approximately ¼ of fleas are engorged with the host’s blood within 5 minutes (B.I AHA course). The flea will then mate on the host and within 1-2 days the female begins laying between 20-50 eggs a day. These eggs will fall off the cat into the environment, such as bedding, furniture and carpet, when the cat moves around.
  • Larva: larvae from eggs hatch within 1 week. Larvae have no legs and they prefer darkness, so they will burrow into crevices and deep into carpet while they develop.
  • Pupa: The next stage of development is pupa. Pupae live inside a sticky cocoon which is very difficult to remove from the environment. This stage usually lasts 1-3 weeks, however pupae can remain within their cocoons for up to 1 year, dropping their metabolic rate during this time because they have no source of food. Pupae wait for a suitable external environment, stimulated by light, warmth and movement (such as a cat walking past) before emerging from their cocoons as adult fleas and immediately jumping onto their chosen host. It is then necessary for these young adult fleas to start feeding on their host as soon as possible before they die.

The timing of this life cycle varies, depending on environmental conditions and how favourable they are to the fleas’ development. The entire life cycle can be completed in as little as 1 week or up to 1 year, but the average time is 1 month. This is important when considering which flea products to use on your cat and how often they need to be administered.

Flea Stages in the Environment - Source: Moxiclear
Another important consideration is that from this life cycle, it becomes apparent to us that the adult fleas feasting on our cats are only a small number of the total flea population in our environment. 

In fact, adult fleas represent only 5% of the total flea population! This means that 95% of flea families are hunkered down in a cosy part of our homes, waiting for the right time to jump up and parasitise our pets. It is vital that we remember this life cycle when treating and preventing flea infestations.

Potential health concerns from fleas:

✔️ Skin irritation and inflammation in reaction to flea bites.
✔️ Anaemia, especially in kittens with a small blood volume. In extreme cases of flea infestation, kittens become very weak and can die.

✔️ Miliary dermatitis is an allergy to flea saliva which can develop if a cat is exposed to repeated flea bites. This can result in excessive scratching and lead to self-mutilation.

✔️ Transmission of the flea tapeworm Dipylidium caninium. While the flea is a parasite of cat, dogs and other animals, it can itself be a host to other parasites. The flea is needed as an intermediate host in order for the tapeworm to complete its life cycle. Because cats can ingest fleas via self-grooming or eating infected prey, all cats should receive regular worming treatment which covers the flea tapeworm.

✔️ Transmission of the Bartonella henselae bacterium, which causes cat scratch disease in humans and is therefore a zoonotic disease. 

Up to 40% of cats are infected with Bartonella henselae at some stage of their lives, although most cats show no signs of illness. On rare occasions it can cause severe organ disease in cats. 

Infected flea dirt gets into the cat’s claws and teeth during grooming and Bartonella henselae transfers from a cat to a human if an infected cat bites or scratches hard enough to break that human’s skin, or if the cat licks an open wound in a human. 

The wound can then become infected and the affected human can also experience signs such as fever, loss of appetite, lethargy, headache and swollen lymph nodes.

Transmission of the Rickettsia felis bacterium, which is responsible for flea-borne spotted fever. This bacterium is found in the flea populations of many parts of the world, as well as other arthropod species such as ticks and mites. It seldom causes active disease in cats. 

Rickettsi felis is also zoonotic and is transmitted to humans when flea faeces enters a human’s broken skin. It was first diagnosed in Australian humans in 2009 when family members were bitten by fleas from infected kittens.

How to tell if your cat has fleas:

✔️ If your cat is itchy /scratching, this should always be

The absence of visible fleas does not rule out a flea infestation, and remember that cats will swallow many fleas during grooming. (Even if fleas are ruled out, it is recommended that other potential causes of the scratching are investigated as there are many parasitic and non-parasitic skin diseases which affect cats).

✔️ If your human family members have flea bites around their ankles, this indicates an environment infested with fleas (in various stages of development).

✔️ Use a flea comb, which has teeth positioned closely together, to brush your cat’s coat, then tap the comb onto a piece of white paper. Flea dirt (excreted blood / flea faeces) looks like specks of dirt, which turns a red / rust colour when moistened. Even if no adults are seen, the presence of flea dirt indicates an active flea infestation.

Treatment and prevention of fleas:

A common error among pet owners is to only treat their pets for fleas during the warmer months (Spring and Summer). While it is true that warmer temperatures prompt the emergence of new adults from their cocoons, remembering the flea’s average life cycle and the fact that these adults represent only 5% of the total flea population is crucial when treating and preventing infestations.

For several years there have been claims of fleas becoming “resistant” to newer commercial flea preparations for pets. While there might be isolated incidences of proven resistance, in the majority of cases product resistance has not been definitively established. 

“The initial response to product failures by practitioners and clients is often to attribute them to insecticide resistance. However, in recent years many of these failures have been ascribed to operational factors. These include the failure to properly treat all pets in a household, to follow label instructions, to continue treatments in winter months, and to properly apply the product to the animal”. (Rust, 2016).

There are many different flea products available, with varying chemical makeups, applications and modes of action. This is not due to a resistance of fleas to particular modern insecticides, but instead a reflection of the huge financial potential in the flea control market (Rust, 2016). Domestic flea products are big business, and manufacturers also recognise the different needs, preferences and lifestyles of pet owners and strive to produce products for owner convenience. 

These include spot-on applications, tablets, chews, injections, sprays, collars and powders, in addition to products designed for treating the environment.

Flea control products vary widely in cost, efficacy and safety, so when choosing one it’s advisable to consult with a veterinary professional (veterinarian or nurse) who has undergone training in parasite control and can help you select the best product for your cat, your family and your lifestyle. 

Cheaper products, especially those found in supermarkets, are not recommended by the author, because their efficacy and safety have not always been established to the standard of veterinary-recommended products. This is especially the case with older-style flea collars and powders. Essentially, you get what you pay for, and it is easy to waste time, effort and money on products which might not give the results needed and which could be unsafe for your cat. If you are uncertain about any product, it is worth asking your veterinary professional for advice.

Another reliable source of information is the manufacturer’s customer help services. It is crucial that you follow the manufacturer’s accompanying written instructions about, how, when, how often and how much to treat your pets, remembering that “treatment failures” are almost always the result of not using a product correctly.

There are 3 broad categories of flea control products:

1. Adulticides. These products kill adult fleas but will not impact on the development of immature flea stages (eggs, larvae, pupae). Therefore, adult fleas will still lay eggs before they die and these will progress to a new generation of adults. In effect, adulticide-only products address only 5% of the total flea population.

2. Insect Growth Regulators (IGR’s). These products interrupt the development of immature flea stages (eggs, larvae, pupae), preventing them from maturing to adults.

3. Combination adulticide / IGR. Many of the commercially-available pet flea products contain both an adulticide and Insect Growth Regulator, enabling them to interrupt flea development at all stages of the life cycle. 

Several of the products also treat other parasites such as ear mites, intestinal worms and heartworm. This is another reason why veterinary advice is useful, in choosing a product which covers all of the important cat parasites and which suits your ability to apply the product correctly (and one which your cat will physically allow you to apply!)

Products available for treating the environment include sprays, “bombs” and foggers. These can be used in conjunction with direct treatments, however these also vary in efficacy and convenience. It is also crucial that safety directions are followed with regards to other pets such as fish and birds and the length of time which should pass before returning to the area.

Product Safety:

Regardless of the product you choose, there are a number of general principles to follow when selecting and using a flea product for your cat:

Only use products which have been licensed for use in cats.

Some dog flea products contain permethrin or related chemicals, which are highly toxic to cats and one of the most common causes of cat poisonings throughout the world [4]

If you also have dogs, do not use permethrin-containing flea products on them because being in contact, as brief as a cat brushing against a permethrin-treated dog, can cause serious illness or even death in the cat.

Permethrin affects the cat’s nervous system and causes neurological signs such as twitching, tremors, increased sensitivity to noise and touch, staggered walking, as well as seizures, blindness and breathing difficulties in some cases [4]. It is extremely traumatising for the cat to experience and for the human family to witness.

If you believe your cat has come into direct / indirect contact with a permethrin (or similar) product, it is essential that you seek veterinary advice immediately, even if your cat does not appear to be unwell. The author has personally treated a cat which was inadvertently given a spot-on dog flea treatment. 

Even though the cat’s owner realised their mistake immediately and washed the product off the cat and sought emergency veterinary treatment, the cat still died from the effects of the toxin. Fortunately, most cats are successfully treated if they receive immediate veterinary attention, however this is definitely a case of “prevention being the best cure”.

In September 2018, the FDA alerted pet owners and veterinarians of the potential for neurologic adverse events in dogs and cats when treated with drugs that are in the isoxazoline class [7]. Pet owners should consult with their veterinarian to review their patients’ medical histories and determine whether a product in the isoxazoline class is appropriate for their pet.

Other product considerations:

✔️ Always follow the product’s weight guidelines; is the dose for kittens, adults, cats <2kg or >4kg? 
Licensed products tend to have a wide safety margin but it is better to regularly weigh your cat to prevent under- or over-dosing. Don’t assume that your cat is a “standard 4kg cat”. For this reason, it is also unadvisable to “share” treatments for a large cat between several smaller cats.

✔️ Ensure you reapply the product at the recommended frequency, all year around.

✔️ Follow any directions for bathing and swimming in relation to timing of product application (if your cat likes getting wet!)

✔️ Ensure the product is age and life-stage appropriate. For example, from what age can kittens be treated, can it be used on pregnant or lactating queens, is it safe to use on cats with various medical conditions (including skin conditions)?

✔️ Treat all in-contact pets, and remember that if your pets go outside they can be exposed to fleas from other animals which have shed flea eggs in the environment (such as the cat from next door which likes to use your garden as a litter box).

Treating the cat's environment:

If you have an active flea infestation, remember to also treat the environment. It is important to treat the environment as well as the pets, because as we have seen from the flea life cycle, existing immature flea stages (eggs, larvae and pupae) will still hatch if they are not removed (however, if an Insect Growth Regulator is used on the pets, future eggs laid - up to 50 per day - before the adult fleas die will not hatch). 

If the environment is not treated during the initial stages, eradicating the flea population can take several months. This is why it is crucial to treat all pets all year around, to interrupt the life cycle at several points.

Wash animal bedding, and soft toys, furniture covers and other soft furnishings in 60⁰ water and hang in direct sunlight. Any immature flea stages which survive the hot washing process will be desiccated in the sun and not develop.

Vacuum all carpets, between floorboards, crevices in lounge couches and chairs and cracks / niches on a daily basis to remove immature flea stages, then apply an insecticide spray containing an Insect Growth Regulator to these areas (follow manufacturer directions regarding where and how to use). Sprays are usually more effective than “bombs” and foggers because the latter products don’t always reach into the niches where immature fleas prefer to hide.

Reduce pet access to areas where flea infestation is possible, such as under the house.

Avoid using essential oils as “home-made” flea treatments. While some commercial products might contain essential oils as part of their chemical make-up, many oils have not been proven to be of benefit and are not licensed for use in cats. 

Some oils, such as eucalyptus and tea tree oils, are toxic to cats [8], especially concentrated oils, and safe doses versus effective doses need to be established.


Successfully eradicating and preventing a flea infestation from your cat and your home requires time, patience and persistence, but with the correct products and professional advice it can be safely achieved. There are so many products commercially available with different modes and frequencies of application and different combinations of parasites they are designed to target. Having so many options is confusing, but take advantage of the many alternatives available and select products which suit your needs, your lifestyle and above all your cat’s and your family’s safety.

Once you have succeeded in making your cat and your home “flea free” ensure you continue to treat all pets throughout the year to prevent reinfestation when the warmer weather arrives. The time, effort and cost associated with year-around prevention is far less than if you let treatment lapse and need to tackle the problem again…from scratch.

written by Candice Drew, August 2020 for Australian Cat Lover (all rights reserved).

About the Writer

Candice qualified as a veterinary nurse in Australia in 2005, being awarded the Novartis Award for Outstanding Achievement in Veterinary Nursing in her qualifying year. 
She has worked extensively in Australia and the UK, and is a UK Registered Veterinary Nurse. Candice is experienced in general practice, shelter nursing and referral nursing (Surgery and Emergency & Critical Care [ECC]). 

She attained the Diploma of Veterinary Nursing (surgical) in 2009, qualified as a trainer & assessor in 2015, and completed the ISFM Diploma in Feline Nursing in 2018. Candice is interested in most aspects of veterinary nursing but her passions are feline nursing, ECC and working with students.

Candice is the happy slave of a 10-year-old rescue cat named “Maggie”, whom she adopted in January 2018.


1. Boehringer Ingelheim: Animal Health Academy for Nurses (accessible only to professionals), Pet owners can access similar information via
2. Centre for Disease Control and Prevention:
3. Cooper, B. (eds): BSAVA Textbook of Veterinary Nursing, 5th edition, BSAVA, 2011
4. International Cat Care: “Fleas and flea control in cats” and “Keeping cats safe: avoiding permethrin and controlling fleas”,
5. Richmond, P.: “A veterinary nurse-led approach to flea control”, The Veterinary Nurse, 2018,
6. Rust, Michael K.: “Insecticide Resistance in Fleas”, Insects 2016, 7,10; doi:10.3390/insects7010010,
8. Benson, K.: “Essential oils and cats”, Pet Poison Helpline,
9. Advantage Petcare: Advantage for cats,