The Life Cycle of Fleas

One of the worst things about fleas is how quickly they breed. Finding just one of these bloodsucking insects means there are almost certainly more lurking nearby! Fleas lay eggs at an alarming rate, so if you find them hopping round in the fur of your pets, there are sure to be more on the way.

Interrupting the flea reproductive cycle (either through the use of adulticides or insect growth regulators) can be the most effective way of eradicating an infestation. However, for these methods to work effectively, it’s vital that you have a thorough understanding of the flea lifecycle. What is the life expectancy of a flea, how long does it take for the eggs to hatch and (most importantly) how quickly do they reproduce? Once you have this information, targeting and killing fleas is a whole lot easier. Read on for the low-down on the life cycle of fleas, so you can take down these bloodthirsty bugs as quickly as possible!

How do fleas breed?

First thing’s first; how and where do fleas mate? Extensive research into the birds and the bees of fleas has found that these insects mate on the host, i.e. in the fur of your cat or dog. This is because the optimal temperature for fleas to mate is between 34 to 42 degrees C, with 38oC (the body temperature of cats and dogs) the temperature at which most mating takes place.

The availability of food is also a key factor for successful breeding in fleas, as female fleas can only lay eggs if they’ve had a blood meal. Once fed, however, an adult female flea can produce more than 20 eggs each day, adding up to hundreds over the course of her life span.

What are the life stages of a flea?

There are four distinct flea life stages: egg, pupae, larvae, and adult.

  1. Eggs: Flea eggs are so tiny they’re almost impossible to see with the naked eye. These smooth, white ovals measure around 5 millimeters in size and drop from the fur of pets (where the female lays them) onto carpets and furniture around your home. The eggs then stay where they fall until they hatch into flea larvae.
  2. Larvae: Flea larvae emerge from the egg as little as two days after they’ve been laid. These tiny, wormlike critters look very different from adult fleas. The eyeless, legless larvae are covered in hairs and measure around 1.5 mm in length with white, segmented bodies. Despite their lack of legs, flea larvae are able to move around in search of food. Unlike adult fleas, larvae don’t feed on blood. Instead, they eat organic matter such as skin scales and flea droppings, which largely consist of undigested blood excreted by the adults. Fleas remain in the larval stage for about 12 days. During this time, they will undergo several molts, during which they shed their old skin. Once they are fully grown, the flea larvae are ready to enter the pupal stage of their development.
  3. Pupa: Once the larval stage is complete, the baby fleas will spin a silken cocoon in which to complete their development. These white cocoons have a sticky outer surface which attracts dust and dirt, helping to disguise them from potential predators and other threats. This means they often look like small balls of dust or lint. Adult fleas may emerge from the cocoon in as little as 4 days, though they can remain dormant inside for up to 12 months depending on climate conditions and host availability. Emergence from these cocoons is usually stimulated by vibrations (caused by a potential host walking nearby) or elevated temperatures.
  4. Adult fleas: The first thing an adult flea does upon breaking out of its cocoon is to look for its first blood meal. This is the only stage of the flea life cycle that lives on a host and feeds on fresh blood. The adult flea is usually just a few mm long, reddish-brown in color and with a laterally flattened body that allows them to move quickly through the fur of their host. They also have powerful back legs, which means they can leap impressive distances. Once they’ve found a host, they will feed at least once a day on the blood of the animal, where they will also mate and lay their eggs.
the lifercycle of dog fleas


How long is the flea life cycle?

The entire flea life span, from egg to adult, takes an average of 30 – 90 days to complete. However, under ideal conditions (i.e. plentiful food supply, optimal temperature, and humidity) fleas may live as long as a year and a half.

How big can fleas get?

The most common types of fleas (cat and dog fleas) usually measure between 1.5 and 3 mm in length. However, some types of fleas (such as the human flea, Pulex irritans) can reach up to 4 mm in length.

Though small, fleas are big enough that they can be seen with the naked eye and are especially easy to recognize from their impressive leap.


Controlling a flea infestation can be tricky but understanding their life span and the reproductive cycle can make things a lot easier. This is because full eradication of fleas often requires multiple treatments to first kill the adults, then take care of any larvae that hatch from the remaining eggs. Knowing how quickly fleas breed, how long they take to hatch from the egg and what stimulates their emergence from the cocoon can help you to more effectively target them at every stage of their life cycle. This allows you to eradicate them from your home (and pets) with as little hassle as possible.

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