Siphonapterology made simple!

Nick McGlennon MA VetMB DVR CertSAO MRCVS

The Flea - What is it?

Fleas are parasites. Defined by the Concise Oxford English Dictionary as 'self-seeking hangers-on' or 'toadies', they live by living on something else, drawing nutriment directly from it. In the fleas case, this means drinking the 'host' animals blood.

Siphonaptera is the Latin name for the collective species of flea and there are around 3,000 different species currently recognised by Siphonapterists in Britain. 95% of these occur on mammals with around 5% occurring on birds.

Whatever an adult flea is living on is referred to as the 'host' and different species of flea are usually named after the 'host' on which they were first discovered or are most usually found - cat flea, dog flea, hedgehog or rabbit flea for example.

However, fleas are not always peculiar only to their namesakes. For example, the most common flea on both dogs and cats is Ctenocephalides felis - the cat flea, but both cats and dogs can also occasionally be affected by other fleas such as rabbit and bird fleas. Ctenocephalides canis - the dog flea (which was previously found in great numbers on dogs, but rarely on cats) is becoming more scarce as dogs are more frequently kept in environments similar to that of our pet cats.

Fleas have been around for millions of years - a fossil flea found in Australia is claimed to be 200 million years old and it doesn't differ significantly from modern fleas. Different species can be found from the Arctic Circle to the Arabian deserts - even penguins have fleas which counteract the cold by ensuring that their growth into adulthood coincides with the time when penguins are sitting firmly on their eggs, thereby keeping both fleas and their young in a warm environment!

Adult cat fleas are generally around 2mm long, with females being larger than males. The largest species of flea is Hystrichopsylla schefferi - a flea found in the nest of a mountain beaver in Puyallup, Washington, USA in 1913. The female can grow up to 8mm long!

During their life cycle, cat and dog fleas undergo complete metamorphosis, going through four developmental stages from egg to larvae, pupae and on to adulthood. As adults, once they have found a suitable host - your dog or cat for example - they will remain there until they die, or are groomed off - their life on your pet is only about 1-2 weeks. It is a misconception that they jump freely to other hosts.

Fleas, in all stages of development, are affected greatly by humidity and temperature - they need water in their environment just as we do and will die without a suitable relative humidity and temperature. The higher the humidity and temperature, the more the fleas like it.

The most important thing to learn about the flea is that it is not the adults that present the main problem in flea control. Research has shown that, in an average household, adult fleas only represent around 5% of a total flea population. Flea pupae account for around 10%; fleas in the larval stages around 35%; whilst flea eggs make up a whopping 50% of the total! Adult fleas will die naturally within one or two weeks following their arrival on your dog or cat. Simply treating your dog or cat with an adulticide to kill the adult fleas, therefore, means that 95% of the flea population are unaffected and are simply left to develop into new adults all around your home.

Dogs and cats, especially those in rural areas, occasionally pick up fleas other than Ctenocephalides felis or Ctenocephalides canis, such as those listed, through burrowing into the living quarters and living environments of the different host species, where newly hatched fleas may be waiting.

Bird fleas can be collected by pets because they are very common in nesting boxes and often migrate out of them. Many drop to the ground from where they can be picked up by our pets.

The Flea life cycle

Understanding how fleas live, and breed, makes it easier to understand the best methods available to eradicate a flea problem.


One female adult flea can lay anything from four to 40 eggs a day, with the highest concentration of egg-laying occurring in the final two to three days of life. Eggs are oval, around 0.5mm long, white and rounded at both ends. The eggs are non-sticky and so, once laid, they immediately fall onto the ground, wherever the pet travels.

Depending upon the temperature and humidity, the eggs will hatch into larvae within one to ten days. Humidity below 50% will cause desiccation and destruction of eggs. The environment in which the eggs are deposited is therefore of prime importance to survival rates and helps to explain why warmer winters and hot summers have increased flea populations considerably in recent years.


A larva will hatch from an egg using a chitin tooth - an egg splitting spine on its head. This disappears when the larva changes into the second of its three 'moults' or development stages. It is this tooth that is affected by modern, oral flea treatments which contain an insect development inhibitor, as the treatment renders the chitin tooth ineffective and prevents the larvae hatching from the egg.

Larvae are semi-transparent and sparsely covered in short hairs. They are usually white with a yellow-brownish head and are generally quite active. They are dependent on a diet of adult flea faeces (which consists mainly of dried blood) for survival, but will also feed on other organic debris in your carpet.

In a home environment, flea larvae are found at the base of the carpet pile, where they can encounter food, are sheltered by the canopy of carpet fibre and can keep away from direct light.

The larvae develop through three moults, or changes, before reaching the pupal stage. The time this takes varies from 7-18 days and is once again dependent on the environmental temperatures. Moisture is vital and relative humidity below 50% will cause desiccation and death.

After the third moult, the larva moves to a quiet, undisturbed place to begin spinning a silk cocoon coated with particles of debris picked up from its surroundings for use as camouflage.


It is within the cocoon that the larvae turns into the next stage of development - the pupa. From this stage, the adult flea develops. The fully formed adult flea remains in the cocoon until stimulated to hatch by, for example, warmth, vibration and exhaled carbon dioxide from a passing pet - or even human!

Development of the flea within the cocoon is also affected by temperature and humidity. Low relative humidity is harmful to the cocooned adult whereas higher relative humidity and higher temperatures result not only in speedier hatching but in bigger fleas!

Pupae subjected to suitable hatching conditions can emerge as adult fleas as early as three to five days following pupation. However, be warned - they can also remain unhatched for up to a year and can cause a re-occurrence of a flea problem if you relax your guard. This phenomenon is known as the 'pupal window' and you need to be aware of it before effective flea treatment can begin.

The pupal window. The pupal window is defined as the period in which fleas are still seen to hatch once an effective flea control regime has been started. By 'effective', we mean a regime that includes an oral insect development inhibitor with or without a household spray.

Environmental sprays and powders can't readily penetrate the cocoon and therefore have no effect on the maturing adult inside if used on their own.

These fleas continue to hatch from their protective cocoons and, unless the flea control regime is maintained, will be the source of the next generation of fleas ready to cause you and your pet more problems!

The pupal window usually only remains 'open' for 1-2 months following the start of a flea control regime but, in some extreme cases, fleas, in their protective cocoons, have been known to live within a house without food for considerable periods of time. This means the pupal window period may extend for several more months after treatment is started.

This cunning feature of the flea is the reason why continuous flea control is needed - the easiest method is to use the new monthly flea treatments simply given to pets in their food.


As soon as possible after the adult flea has hatched from the cocoon, it will begin looking for its first blood meal. Unlike the flea larva, which tends to move downwards and away from light towards protective covering (e.g. the carpet base), adult fleas move upwards and towards the light, in order to be in a better position to locate a suitable host.

A flea's eyesight is not brilliant and so air currents and carbon dioxide in the air appear to be responsible for helping the flea find a target. Air currents will be caused by a cat or dog moving past the adult flea, whilst the carbon dioxide increases are caused by the cat or dog breathing in close proximity to the waiting adult.

Adult fleas have been known to jump as many as 10,000 times in succession, whilst trying to leap onto a passing cat or dog - the flea knows they are close by but it's more a question of luck than judgment when trying to make a successful connection between the hooks on the flea's legs and the fur on the cat or dog.

However, once satisfactorily 'anchored', the flea will immediately begin to feed with females starting to lay eggs within 48 hours of the first feed.

Before taking in blood, the flea secretes saliva into the wound. This contains a substance that softens and spreads the skin tissue, assisting with penetration. The saliva also contains an anticoagulant to help with the feeding. It is flea saliva that is usually the cause of allergic reactions in cats, dogs - and humans.

Once on a suitable host, the adult fleas will remain there until they die, which is usually within one to two weeks. Unfortunately for the pet (although fortunately for the flea population) female fleas tend to live longer than males - there are also more females than males. If a dog or cat is left to groom itself normally (and cats groom more thoroughly than dogs on the whole), many adult fleas will also be dislodged or swallowed naturally. However, if for any reason, a cat or dog is unable to groom itself - it may be ill for example - then the owner should groom it more frequently than usual, to mirror the pet's natural methods of flea control.

Has your pet got fleas?

In all likelihood, the answer is 'yes' even if it's not immediately obvious. There are around 14 million cats and dogs in Britain today and all pets will, at some time in their lives, be irritated by fleas.

Fleas are the most common cause of skin disease in cats and dogs. Many vets confirm that up to two thirds of their time, especially in the summer, is spent treating flea-related conditions in pets.


Everyone believes in the logic of using a smoke-alarm as an early warning system for a fire - the same logic should be considered when dealing with fleas. Don't wait until you have to call out the fire brigade to deal with a 'flea fire'. Don't leave the problem until it has become so serious that your pet is really uncomfortable and you have fleas jumping all over the place-household infestations can be very difficult to control. More importantly, the longer you wait the more seriously your pet will be affected and the longer it will take to clear the problem.


Aside from suffering from flea bites yourself (guaranteed to make any pet owner address the problem rapidly!), there are three easy 'early warning systems' you can use to check for the presence of fleas on your pet:
  1. The pet will be scratching itself frequently or in a very agitated manner. All animals - like humans - will itch occasionally but you should be able to recognise if a pet develops a recurring and irritating itch from having fleas. A flea itch is not usually caused by the adult flea moving around on the animal's skin. It is more normally caused through the pet developing an allergy to the flea's saliva.
  2. Not all pets will show an allergic reaction however. Just like humans, some are affected and some not. So another way to spot a flea problem is by recognising flea droppings in the pet's coat. If you groom your pet regularly, you may find flea droppings amongst their coat. These are small and black, and resemble ground pepper. They are made up of blood and secretions from the adult flea and should not be confused with live adult fleas which are bigger and move considerably faster! Droppings will dissolve on a moist piece of cotton wool, leaving a red dot.
  3. Any evidence of skin disease can have fleas as the primary cause. So if your dog or cat exhibits any hair loss, soreness or skin problems, take it to your vet. Don't just hope it might 'go away' - it will probably get worse.
Grooming. If possible, always groom a pet outside as newly laid flea eggs will then fall off outside. The lower temperature and relatively low humidity levels will help to ensure that fleas - in all stages of development - will find it that much harder to live.

Environmental 'Hot Spots'


An 'environmental hot spot' is an area where flea eggs, larvae, pupae, and adults waiting to hatch, are more likely to be lurking. The basic rule is that not all areas of the house and surrounding area will be suitable for fleas to breed but a careful eye should be kept on anywhere where the pet is a regular visitor.


Areas that are good for flea development in the house are the pet's bedding, thick carpeted areas which the pet frequents regularly, and carpeted or dirt floor basements. Anywhere the pet sleeps - on throw rugs, blankets, or in baskets - will be a prime candidate for a hot spot. If you allow your pet to lounge around on sofas and chairs, then these could be 'hot spots' as well.

Places such as tile floors are less likely to support development as they can be more easily kept clean. Well traveled hallways are also less likely 'hot spots' as the constant vibrations and air currents will ensure that fleas hatch quickly and can find a suitable host in a shorter time, thereby not lurking around for long.


These are very uncommon in the UK climate, but potentially favourable areas where the flea life cycle could develop are where there is moist soil and shade. Areas like this might include an outside dog house, flower beds and damp areas under bushes. Any other shady places where pets might rest during the heat of the day could also become hot spots for fleas; occasionally it has been known for the car to become a breeding ground!


Try and identify as many 'hot spots' as possible before any treatment of the animal or the environment begins.

Start your flea control offensive inside the house but ensure that you regularly vacuum chair covers and rugs, and any bedding used by your pet. Regular washing of bed linen and loose covers also sorts the problem out.

Vacuuming, especially if you have a 'beater bar', will remove some flea eggs and a certain percentage of flea larvae (although spines on the larvae's bodies can make them difficult to dislodge). The vibrations will also stimulate adult fleas to emerge from their cocoons but make sure that you empty out the bag every time you vaccuum otherwise the fleas will simply continue their life cycle inside it.

Remember to vacuum down the sides and underneath sofas and chairs and in dark corners. Flea larvae move away from the light and so, although most larvae will be found where the flea eggs are deposited, they can travel up to half a metre away from these areas.

Environmental flea sprays, containing long acting insecticides or insect growth regulators are useful and s hould be used according to the manufacturer's instructions. Fleas in their larval stages, hiding deep down in carpet fibres and in dark nooks and crannies, are much more difficult to get at with conventional sprays and the silken cocoons spun during the pupating stages are impervious to them.

Unlike larvae, adults move upwards towards light as this makes it easier for them to locate a host. It also means that they are more easily affected by household insecticidal sprays.

Outside the house, mow or clip the areas under bushes and remove leaves and other debris to allow these places to dry out. Try and keep piles of refuse or wood to a minimum and keep them as dry as possible.

Flea Treatments

Flea treatment has undergone many changes, with some products disappearing and others emerging. Now that the full story behind the flea and its remarkable lifestyle has been explained, we hope that it will be easier to understand why some methods work better than others.


Having established that adult fleas represent only 5% of the total flea population and that female fleas lay their eggs not only very quickly after finding a host, but also in large amounts, it is easier to understand why simply killing off the adult flea is not an efficient method of flea control.

Dr John Maunder of the Medical Entomology Department at the University of Cambridge, is one of Britain's leading flea experts. He has this to say about the successful treatment of fleas:
'Flea control is best directed at the free- living stages, which is the one thing that until now has been difficult to do. Insect growth regulators are a new feature in the flea control area and a new compound, lufenuron, a systemic insect development inhibitor seems to provide the answer. It is the effect of lufenuron against the immature stages of the fleas which is the most effective plan of attack.'


The way in which our dogs and cats live with us - inside; outside; in rural and urban environments; able to roam freely or being taken for walks; restricted to certain rooms in the house or allowed access to everywhere - will have an effect on the way fleas are able to breed. It will also make a difference to the type of flea problem that you and your pet are suffering from.

The following offers advice on the most effective means of attack - from taking preventative measures to a void a flea problem altogether to tackling a severe infestation of both pets and household.


You must treat all your dogs and cats for fleas at the same time, in the same way. Simply treating one pet, and ignoring the others, will be a waste of time and energy for all of you, as will using one treatment on one pet and a different one on another.

Make sure that you strictly follow the manufacturer's instructions for any treatment you decide to use - failure to do this may not only be dangerous but will usually result in the treatment being ineffective.


The best method of defence is attack! Even if you don't see any evidence of fleas on your dog or cat, the chances are that fleas will occur, picked up from anywhere the pet visits, or from flea eggs dropped by another pet visiting them. The colder, damper winters may lull you into a false sense of security but, once the warm weather starts, fleas will become more and more evident.

Use of an insect growth inhibitor before a flea problem begins is therefore the best way to counteract the chances of infestation. Insect growth inhibitors, such as Program from Ciba Animal Health, are available from veterinary surgeons and are simply given to your dog or cat, once a month, in their food. Safe enough for use on puppies, kittens and pregnant pets, the use of Program will ensure ensure that any adult fleas which do manage to get to your pet, will lay eggs which are unable to hatch, thereby stopping the life cycle in its tracks.

Monthly use throughout the year will keep your home from becoming a 'home from home' for these unwelcome 'flea loaders'!

Check for any new 'hot spots', groom pets, wash their bedding and any loose covers, and vacuum regularly - clever they might be but with a little thought and advance planning, fleas can be beaten - for good!


This can happen at any time of the year. With central heating, carpeting and, therefore, higher humidity, in many pet-owning households around the country, fleas are finding it easier to breed. You may have suddenly noticed an increase in scratching from your cat or dog and may have actually spotted one or two fleas.

Could this be because you thought winter would see off the flea problem and so stopped any treatment of your pet? Probably!

Start your pet on lufenuron and, at the same time, use an 'adulticide' flea treatment on the pet until the infestation is under control. This will have the effect of killing off as many adult fleas as quickly as possible whilst rendering any that have the chance to feed off the pet infertile and unable to continue the life cycle.

Insecticides for use on pets come in many types, presentations and duration of action. All on-animal insecticides are licensed and are therefore safe to use as directed. The choice of preparation tends to be due to either vet or pet owner preference. Sprays or low volume 'spot-on' formulations are the most popular compared with powders or collars.

In the past the on-animal insecticide approach to flea control has had the most attention. However, as knowledge of flea biology has increased, the realisation that the key to effective flea control was to effectively break the life cycle rather than just kill the 5% of adults on the pet has focused the attention on the newer insect development inhibitor approach.

All insectides have the same weakness in that efficacy gradually wanes and at some stage viable flea eggs are once again dropped off into the environment to start the life cycle again. Owners are reluctant to continually coat their pets with insecticides, however the concept of the continuous protection that can be given using a product that acts only on insect tissue has found favour and is now a market leader in flea control.

Keep up the regular washing of your pet's bedding and clean and vacuum around the house. Continue to use lufenuron monthly to prevent the problem happening again.


OK - you left it too late again! Your pet and your house are literally jumping and the fleas are leaping up and down with excitement - you may even be being bitten yourself!

The best method for an emergency like this is a three-pronged battle plan: start your pet on lufenuron, to ensure that any new flea eggs are infertile when they are laid. This is the beginning of the end of the infestation.

Use an adulticide on the pet to help rid it of as many adult fleas as quickly as possible. At the same time, use an environmental spray treatment around the house. Pay particular attention to the hot spots where the pet frequently goes. Continue to regularly wash bedding, and clean and vacuum clean.

In cases of severe infestation, don't be discouraged if it takes a couple of months or longer to rid the pet and house completely - fleas are incredibly tenacious but they will disappear eventually.

The most important piece of advice to remember is don't leave it too late again! Just because you can't see fleas jumping, it doesn't mean they are not there. If you have a pet, always assume that the fleas are lying in wait and treat them accordingly. The monthly use of an insect development inhibitor throughout the year will ensure that, when the summer arrives next year, you will have peace of mind that your house will no longer be a sanctuary to fleas - the flea explosion won't even be a damp squib!

The final word!

This must go to Don Marquis, who wrote in 'Archy and Mehabitel' in 1927:
'Insects have their own point of view about civilisation; a man thinks he amounts to a great deal, but to a flea or a mosquito, a human being is merely something good to eat'.

If you have any queries about the use of the product Program mentioned in the article then contact Ciba Animal Health on 0345 573912 9am to 6pm Mon-Friday (UK only)

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