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The Flea Lifecycle

If you understand this lifecycle of fleas it will really help you get rid of them sooner and explain why it can be normal to occasionally see some fleas even on treated pets.

Take a moment to read through this article and equip yourself with some useful flea knowledge… Fleas are biting, wingless parasites. 1-2mm long black or brown with narrow bodies for darting through animal fur and short with powerful legs for jumping from the ground onto different hosts.

Why are they such a problem?

They cause distress to pets and owners and lead to the most common skin problem that vets see. If allowed to go unchecked their population can BOOM and lead to conditions ranging from annoyance (itching and scratching) to hair loss, through to Flea Allergy Dermatitis (FAD) which is often associated with secondary bacterial skin infections requiring veterinary care. Flea Tapeworm and Anaemia add to the list of problems that fleas can cause. Once they infest a house or environment they can take many weeks of time, effort and cost to get rid of, and can bite humans as well as pets. Basically, they are a down-right nuisance!

Flea Allergy Dermatitis

Flea Allergy Dermatitis is the most common skin condition in dogs and cats. It is caused by a hypersensitivity to proteins in flea “saliva”, which is injected into the skin as the flea feeds.

The degree of sensitivity to fleas will vary from animal to animal, with extremely sensitive animals requiring very few flea bites to trigger the allergic response.

Treatment is aimed at eliminating fleabites. Eliminating fleas from the environment and the animal is important. An animal treatment that kills fleas on contact with skin, and doesn’t require them to bite can be really useful to reduce the amount of allergen delivered to your pet. Your vet may prescribe medication to help relive itching and sometimes antibiotics or washes are used to control secondary bacterial infections often introduced by the self-trauma of scratching.

Flea tapeworm

Flea tapeworm (Dipylidium caninum) is the most common tapeworm in dogs and cats. The flea is the intermediate host and the cat or dog is infected when they accidentally ingest an infected flea when trying to nibble or groom irritating fleas off their skin.

The flea tapeworm can cause an itchy bottom and as such is a “socially unacceptable” parasite causing dogs to rub their bottom on the ground... and cats to groom their bottoms a lot!

Flea tapeworm can be evident around an animal’s bottom or in the faeces where it looks like grains of rice or cucumber seeds. Yes – it is truly YUK!

It can also be passed to humans. Eliminating fleas stops animals becoming infected, along with worming with Drontal® to get rid of any existing infection. Although not a common problem, humans occasionally become infected, mostly children.


In untreated young, old and arthritic animals that are not able to eliminate adults through grooming, large numbers of fleas can rapidly accumulate. The flea is a voracious feeder and the removal of blood can be severe enough to cause anaemia during heavy infestations. This is more likely to occur in smaller animals of lower body weight. • 100 fleas consume over 1 ml of blood per day, which in very small animals, like kittens, can represent around 3-5% of total blood volume. This can lead to debilitation, weakness and even death in puppies and kittens.

The Flea Lifecycle

There are around 2000 different flea species in the world but the Cat flea (Ctenocephalides felis) is the most common flea we see on both dogs and cats. Found on prehistoric fossils from the dinosaur era, fleas have evolved with clever adaptations to become long lasting and successful parasitic pests.

The flea life cycle has 2 phases; the on-host parasitic phase of the adults and the off-host/environmental stage of the eggs, larvae and pupae - this makes them tricky to eradicate! The time it takes fleas to reproduce is hugely variable – when all the temperature and humidity are optimal, new fleas can be created within 12 days, but when temperatures and humidity are too high or low, it can take 6 months to occur.

Why is the flea life cycle important?

Well, we need to think of the whole flea population as the problem, not the just the visible fleas on your pet. For every flea you see on your pet there are probably many more but they are good at hiding in their hair! Seeing 5 fleas on your pet also means that somewhere in your pet’s environment there are about 100 more lifecycle stages undergoing development to become new fleas. The adult fleas we see are actually just the tip of the flea iceberg!


Newly emerged fleas are able to survive for up to 2 weeks without food in the environment, just waiting for a host, but once on a host they feed almost immediately.

They feed voraciously in bouts of 2-3 minutes consuming 18-33% of their body weight in blood in each meal.

They don’t digest blood very well producing 8-10 droplets of protein rich faeces after each meal, which rapidly dry to become what we know as Flea Dirt. The flea dirt is virtually undigested blood and makes the ideal food for larvae in the environment.

Within a day of jumping onto an animal, fleas will mate and within 2 days will produce eggs. Female fleas produce a peak of 50 eggs per day within a week and produce on average 2000 eggs in their lifetime. Adult fleas can survive for up to 120 days but many fleas are removed by the animal grooming itself. In ideal conditions 10 fleas can become 1/4 million in one month if left untreated. Yikes – it’s easy to see how a population can grow into a real problem very quickly!

Once they have fed, adult fleas are dependent on a continuous supply of blood for survival. If they drop off their host they can only live for 3-5 days.

Fleas don’t often jump around from host to host, so if your pet has new fleas they most likely picked them up from somewhere else in the environment.


When fleas lay eggs they are moist but rapidly dry and become very hard to kill. They tend to be laid when the host is resting and passively fall off the host when the host gets up, or if an animal shakes itself. In this way your pet can act like a salt-shaker, dropping flea eggs on to the floor around them.

Eggs fall in areas where animals rest and other areas where animals perform repeated vigorous movement, such as doorways where animals jump up and down waiting to be let out or in. Flea eggs are deposited along with flea dirt, which forms the basis of the diet of larvae. The eggs hatch within 1–10 days. Like all the life cycle stages they prefer warm not hot conditions with high humidity. Low humidity dries out eggs and they fail to hatch. Eggs that drop in the middle of a concrete path in a dry spell are unlikely to survive while eggs that fall in an animal’s favourite resting spot under a bush are protected from the extremes. Flea eggs land wherever they have been dropped and can’t move themselves, so you can physically remove up to 90% by vacuuming areas thoroughly.


The next life cycle stage is the flea larvae… which can wiggle up to 50cm on their own… so are harder to vacuum up. Most larvae emerge/hatch within 2-6 days and immediately start to consume flea dirt. Larvae don’t like light, so crawl into cracks and crevices between floorboards, into the carpet fibres, or under leaves and debris in the garden. Like many stages of the life cycle the flea larvae are prone to desiccation (drying) and excessive heat. When disturbed, flea larvae wrap around objects holding onto their positions. A good example of this can be seen when they curl around carpet fibres to hold on to them. Even fastidious vacuuming only removes around 15-27% of larvae.


The flea life cycle then enters its most difficult to counteract phase – Larvae spin a tough cocoon around themselves, protected from environmental conditions – (similar to a butterfly developing by metamorphosis in a chrysalis…just not as pretty!) In this cocoon, pupae develop into fully formed pre-emergent adults that sit in waiting and hatch out in response to stimuli such as body warmth or pressure, carbon dioxide in exhaled air and vibration of a potential host passing… they can basically detect when a new host is in the area and emerge in time to jump onto them to start the life cycle all over again. As said before, they are pretty clever! The cocoon silk is sticky so surrounding debris attaches, which camouflages and helps protect this stage from insecticides and climate extremes. Also as cocoons are formed in hard to reach positions, like deep in the leaf litter or carpet, there is little that can be done to kill the flea at this stage of their life cycle.

Even flea sprays, foggers and bombs are unable to penetrate carpet fibers deep enough to kill all these developing adults.

The pupae develop into pre-emergent adults within 5 days under ideal conditions (warm and humid) and can last up to 140 days. It takes really low temperatures such as 3°C for 10 days or -1°C for 5 days to kill development at the pre-adult stage, and that’s why fleas can survive winters in New Zealand.

Have you been unlucky enough to experience a “flea plague” when returning from holidays? This happens because while you were away, the entire off-host life cycle stages have developed into pupae. Whilst the house was empty there was no stimulus for the pupae to hatch, nothing happened. When you return, lots of hungry pre-emergent fleas hatch at the same time as they sense the presence of new hosts… and the carpet can seem alive with jumping fleas! The emergence of new adult fleas from their cocoons explains why some people keep seeing fleas on their pets for many weeks after commencing the use of flea control. This may occur for up to 6 months but usually peaks in the first month.

You are now a mini flea expert! You understand flea biology now so should be able to tackle them head-on! Read our Tips for fighting fleas on your pet and in their environment.

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