Professional Pest Controller Magazine Issue 93

07 December 2018

Pestwatch: Cat and dog fleas

Technical | PPC93 December 2018

In this in-depth PestWatch analysis, BPCA Field Officer, Natalie Bungay, investigates cat and dog fleas, paying particular attention to the sources of infestations even when a host appears absent.


Without a doubt, the most common fleas we Brits will encounter is the cat flea Cteneocephalides felis and then more occasionally, the dog flea Cteneocephalides canis.

Fleas are probably a pest that most people at some point have experienced – be it at a place of work or in their home. Most issues will be related to domestic pets picking up the problem from an outside source. Whether it be a curious dog who comes across a healthy fox den, or a sociable cat taking home its friend’s bloodsuckers, our beloved pets are usually the source of these pests.

However, sometimes, it may seem like a report of flea activity is unwarranted and confusing – especially in a medical records office within a hospital, or reception area of a commercial building.

What is the source of the infestation then? You’ll need to conduct an investigation and set up some monitoring to establish what exactly is causing this ‘outbreak’. But before we tackle monitoring and treatment, let’s start with a bit of background...

A short history of fleas and their ecological significance

Over 2,500 species of fleas have been described worldwide and, fortunately, we are familiar with a tiny group.

Contrary to popular belief, it was not one of the previously mentioned fleas that were responsible for the spread of the infamous plague. It was, in fact, the oriental rat flea Xenopsylla cheopis, which is a vector of Yersinia pestis, the bacterium which causes bubonic plague.

The disease was then spread by rodents such as the black rat, which were bitten by fleas that then infected humans. Major outbreaks included the Plague of Justinian and the Black Death, both of which killed a sizeable portion of the world’s population.

It’s believed fleas were once free-living, flying insects. Then they started living within the dens of small mammals, feeding on the debris there. Eventually, they started feeding directly from the animal. Through the slow process of natural selection, fleas lost their wings.

If you think about the benefits of fleas regarding the food chain, environment and so on, it could be argued that fleas (like all species) are merely filling an available ecological niche. All organisms are part of the food chain; whether they are consumed by animals, microorganisms or fungi, fleas help keep nutrients flowing through the system of life.

You could (controversially) argue that bloodsucking parasites help to re-balance populations that are out of control by being vectors for disease. That’s all well and good until it’s your species that’s under the threat of disease and death!


    • Fleas are related to Diptera (true flies) and were once free-living, flying insects
    • Neither cat or dog fleas were responsible for outbreaks of plague
    • Cat and dog fleas can feed off different hosts, but if they do, they won’t be able to produce viable eggs
    • One flea could potentially produce 8,000 eggs in her lifetime
    • Fully formed fleas can remain in their cocoon waiting for signs of a host
    • Formication is the sensation resembling insects crawling on or under the skin.

Significance of flea lifecycles

Significance of flea lifecycles

Unlike the names suggest, C Felis and C Canis will not dedicate to one host species, they can feed from various animals. Although they will be able to feed and sustain themselves for a period of time on a different host (for example, human blood), they will not have the ability to produce viable eggs.

This means that if you’re certain that no host animal is present, then the flea activity will stop all by itself… eventually!

To understand why the problem seems to persist without a host animal, we have to look at the lifecycle of a flea.

The flea goes through a complete metamorphosis: egg, larval, pupal and adult.

Egg stage

An adult female flea that has had a full blood meal will begin to produce 20 to 30 tiny (0.5mm) non-adhesive white ovoid eggs per day. She’ll lay them at a rate of about one per hour until she dies.

Under ideal conditions, it might be possible for her to produce 2,000 and 8,000 eggs in her lifetime. However, most only manage to produce around 100 before being consumed by their host while grooming!

The eggs are dispersed freely into the environment. Within two to seven weeks a certain proportion will then hatch into larvae.

Larval stage

The larva of the cat flea has a grub-like appearance and is about 2mm in length.

Larvae actively avoid light and hide in the appropriate areas around them. The larvae require adequate ambient moisture and warmth and will die at temperatures near freezing.

They will feed on a variety of organic substances, but the most important dietary item for them is the crumbs of dried blood that continually fall like snow out of the haircoat of the host after it has been excreted by the adult fleas as faecal material. Thus, the adult flea population continually feeds the larval population in the animal’s environment.

Pupal stage

The larvae then begin spinning a cocoon and entering the pupal stage.

The cocoon is adhesive and quickly acquires a coat of camouflage from surrounding dirt and dust. Pupation depends heavily on temperature and moisture and takes a week or more to complete.

A fully pupated adult can remain inside of its cocoon in a state of semi-dormancy (called the ‘pupal window’) awaiting signs of the presence of a host - something I’m sure we’re all very familiar with. It is this stage that causes the extended periods of flea activity with no host present. There could be hundreds, even thousands of formed adults waiting in pupal-silence for their next victim to approach!

It may take more than one ‘disturbance’ to encourage all of the adults out of the relative safety of their cocoon so keep this in mind when you’re scratching your head over extended flea issues.

Adult stage

The new flea begins feeding on host blood within minutes and will then begin the cycle again, feeding, reproducing and dying!

Treatments and monitoring

First, we need to establish if there is an actual infestation using monitoring methods. CoSHH does not allow us to use insecticides as a precautionary method, and rightly so; we need to confirm the presence of fleas.

Sometimes it may be evident that fleas are present by visual sightings. In the absence of this, we must use a light and heat monitoring trap, which are widely available from your suppliers. Place various monitors in appropriate locations around the property and wait to see what is caught. If a customer is happy to do so, you can rely on them contacting you in the event of any capture.

If no fleas are detected, then no pesticide treatments can go ahead. It’s the law.

Look outside the box

Most of us will have experienced the odd tricky confirmed flea problem that seems to go on and on with seemingly unsuccessful treatments.

The important thing to do is ask lots of questions; How long has the issue gone on for? Who else has been in the property? Has it been vacant awhile? Are there any possibilities that a wild animal is entering the space?

This last question may seem far-fetched but I have actually experienced something of this nature. I once worked within an NHS facility, and their medical records department constantly suffered from flea problems and, trust me, there were fleas there - a lot of fleas! Each time a treatment with insecticide was carried out, the fleas would die, and we saw evidence of this. However a week or two later, more fleas would appear. This was frustrating to say the least.

After about three months, during a night inspection for other pests, I noticed a window open in one of the side rooms within medical records. The next day I spoke to the manager, and this is where the resolution to the flea issue was discovered! The manager said, “Oh yes, we leave that window open - actually, most mornings we do find fox faeces on the floor of medical records which we just clear up.”

So, in the end, the solution to the flea problem was closing the window. After this not a single flea problem was reported again.

Always ask the questions. It can help you build a picture of what’s going on.

Delusional parasitosis (DP)

Delusional parasitosis DP

DP is a disorder in which individuals incorrectly believe they are infested with parasites, insects or bugs when, in reality, no such infestation is present.

Individuals with delusional parasitosis usually report tactile hallucinations known as formication, a sensation resembling insects crawling on or under the skin. DP is a mental disorder characterised by a fixed, false belief that a skin infestation exists, which is in contrast to cases of actual parasitosis, such as scabies.

The aforementioned monitoring procedure can help to show sufferers of this condition that their issue does not lie with fleas, and that their next step should be to see their GP. We must not be tempted to use pesticides to alleviate sufferers’ concerns. Again - it’s the law!

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