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February 10, 2010 by Shaun Day


There are over 2,000 recorded species of fleas (order Siphonaptera) in the world with around 100 in Europe and 60 or so species in the UK. They are wingless insects; external parasites of warm-blooded animals whose mouthparts are adapted for piercing skin and sucking blood.  Their bodies are hard and flattened from side to side, helping them move about in the fur of a variety of host animals including pigs, hedgehogs, foxes, dogs, humans and cats. The majority of species feed on mammals and around 10% live on birds.

Although they cannot fly, fleas can jump rapidly using their relatively long legs and a spring-like mechanism in their body. The cat flea the most common domestic flea – can jump at an acceleration of 130 times that of the strength of gravity. Other common fleas include the dog flea, the human flea, the rabbit flea and the oriental rat flea, together making up a family of fleas known as “Pulicidae.” Cat and dog fleas are anatomically similar meaning cat fleas can infest dogs and vice versa.

Dog flea (Ctenocephalides canis)

Dog flea (Ctenocephalides canis)

The Flea Life Cycle

There are four major stages of the flea life cycle: egg, larva, pupa and adult. It takes a cat flea around 30 to 40 days to complete the full egg to egg process although some cases have shown the cycle to take up to a year.

The female flea begins laying eggs within 2 days of her first blood meal. The eggs are white and tiny (0.5mm) but are visible to the naked eye. Eggs are laid on the hairs, feathers or in the habitat of the host; they then fall onto places such as the carpet, bedding or furniture. Some fleas lay in batches of three to eighteen eggs at a time, potentially laying a total of 500 eggs over several months. The eggs hatch in one to twelve days after being deposited producing worm-like larvae which have no legs and no eyes.

Flea larvae are white and 1.5-5mm in length with a sparse covering of bristles. They rarely live on the body of their host, instead they immediately seek enclosed areas such as pets’ beds, carpet fibers and cracks in the floor where they  look for food whilst avoiding light. Larvae feed on a variety of organic material including fallen skin scales, animal waste and adult faecal matter (consisting of relatively undigested blood). The larvae shed their skin allowing them to grow and spin silken cocoons over a period of 5-15 days. The larva rests as a pre-pupa for 3 days before moulting again to form the pupa.

Flea larva

Flea larva

The pupa develops within the cocoon from five days to five weeks in the absence of hosts. Under normal conditions, adults are ready to emerge after roughly 2 weeks but at higher temperatures development is quicker. They sometimes remain in the cocoon until a vibration or noise is felt (indicating the presence of a human or animal) meaning – in the absence of movement – adults can stay in the cocoon for up to 6 months.There are many reports of homes “coming alive” with fleas when the residents return after some time away and disturb the cocoon bound fleas.

Adult fleas are reddish-brown/black, wingless, measure 2-8mm in length and are laterally compressed. They are covered in bristles and combs which help them to cling to hosts and have antennae which can detect exhaled carbon dioxide from animals. Their antennae are also sensitive to heat, vibration, shadows and change in air currents. All fleas rely on blood for their nutrition but are capable of living long periods of time without eating, usually around 2 months. In favourable conditions and accompanied by a reliable source of blood meals, fleas can live for up to a year.

The Problem with Fleas

Fleas are primarily a source of irritation to humans and animals; however the unique features of a flea’s mouth give them the potential to spread various pathogens which can have severe consequences. The dual function of a flea’s mouth allow them to both squirt saliva and blood into the bite, whilst sucking up blood from the host. This, along with the flea’s ability to transfer from one host to another, makes them effective in spreading bacterial and parasitic diseases.


Some people are resistant to flea bites, often living with fleas constantly and not realising they’re present. The majority of people however are sensitive to flea bites, which are often found on the legs of people in flea infested areas. The bites swell up, are irritating and appear as a small red spot surrounded by a red halo. For those who have sensitive skin or who have certain allergies, a flea bite can cause hives, rashes or generalised itching. The allergic reactions appear 12 to 24 hours after a bite, and may last a week or so. Children are particularly vulnerable to papular urticaria, a skin reaction caused by flea bites (and sometimes mites) which produces inflamed spots and blisters for up to a few weeks.

The majority of cats and dogs will have some itching after a flea bite, but more serious effects can occur if a pet develops flea allergy dermatitis. In this instance one or two bites can cause severe itching, reddening at the site, hair loss and the likelihood of a secondary infection due to scratching. These symptoms last up to 5 days.

dog scratching


Cat and dog fleas can serve as intermediate hosts for the Dipylidium caninum tapeworm. Adult fleas can carry tapeworm cysts and transmit the parasite to pets if ingested.


The Black Death (a collective term for the outbreak of the bubonic, pneumonic and septicemic plagues) caused around 100 million deaths in the 14th century and spread globally. The disease was caused by the Yersinia pestis bacterium, primarily hosted by the oriental rat flea. If a flea bit a diseased rat, the bacteria would overcome the flea’s digestive system, causing it to experience an unquenchable hunger. Infected fleas would then bite humans and transfer the plague bacteria via the wound.

Flea Management

There are multiple factors for consideration when attempting to manage a flea infestation, with many flea control products available to help the problem. Removing fleas from an animal alone would not eradicate the population, as fleas that are in the earlier stages of the life cycle would still be developing away from the host animal. Once the life cycle is considered, it becomes easier to see the necessary steps to take when trying to eliminate a flea infestation and to prevent one from reoccurring. The detection of fleas is simple. If a pet is scratching or there are bite marks around someone’s ankle, a quick inspection of the pet’s fur or bedding will reveal any flea infestation as they and their faeces are both visible to the naked eye.


Treating pets for fleas directly is the first step to take when tackling a flea infestation. A flea comb works by trapping fleas within very fine teeth which keeps them on the comb or forces them to jump off. Shampooing pets is a popular method of flea removal. Dried blood and skin flakes are dislodged leaving no food for flea larvae. It is recommended that the shampoo is lathered throughout the animal’s body and left for up to 15 minutes, followed by a rinse. Insecticides such as pyrethrins, pyrethroids and deltamethrin are contained within certain shampoos which kill fleas immediately. Some insecticides have better residual properties than others. All animals within a home should be treated even if they are not showing obvious signs of infestation.

Insect growth regulators (IGRs) and insect development inhibitors (IDIs) are used to interfere with the flea life cycle. They cause incomplete egg development and premature moulting of adolescent fleas. Popular IGRs include methoprene, hydroprene, and piriproxyfen. IGRs prevent flea larvae from turning into adults, and have a residual effect of almost three months. Products such as Program® are designed for internal use and come in the form of a pill (for dogs), a food additive (for cats) and an injection (for cats). The active ingredient in Program® is lufenuron which is stored in the animal’s body fat and inhibits further reproduction of fleas that have bitten the animal post treatment.

Flea on Nail

In the Home

Eliminating fleas from the home requires both planning and persistence. Most flea eggs and larvae will be located in areas frequently visited by the household pets so these areas should be where treatment is concentrated. Vacuuming is usually the first step to take. This will capture adult fleas as well as dislodging and removing flea eggs and larvae from bedding, furniture, carpeting etc. The vibrations will also stimulate developed adults to emerge from their cocoons to then be captured when repeating the process. Larvae have an ability to attach themselves to carpet fibers but this can be overcome by steam cleaning carpets if necessary. Alternatively, borate-based products can be applied to carpets which poison flea larvae upon ingestion. Pet’s bedding should be washed and insecticide sprays administered post vacuuming. Flea light traps exploit the flea’s instinctive attraction to heat and light. A trap consists of a bulb that flashes on and off which causes the flea to jump towards it as this simulates a potential host passing by. The fleas are then trapped on a sticky surface positioned under the bulb.

Pest control

2 responses to “Fleas”

  1. Bernie Poole says:

    This is an excellent overview of the world of fleas and I would recommend it highly to anyone who either has a problem with fleas or who hopes to avoid such a problem. Knowledge is power, as they say, and the secret to staying on top of any flea or other infestation is to know as much about the critters as possible. This article is a good start.

  2. Paul @ Allergies In Dogs says:

    @Bernie – I agree, there is good information in here that pet owners need to be aware of.

    It isn’t too difficult keeping your pet free of these parasites with a little forethought and the right products.

    I’m glad you included the info aobut the fleas possibly transmitting tapeworms. Many people think a few fleas are no big deal, but if they knew about them carrying tapewords, they might realize how important flea control is!

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