How fast do fleas spread?


Fleas are highly reproductive. They multiply and spread quickly. On average, a female flea lays 25 eggs per day. And she’ll survive for 7 days. Eggs reach adulthood in 17 to 26 days. So, within a month, she’ll have thousands of descendants, but most won’t reach adulthood.

Most eggs won’t survive, due to being infertile, cannibalized by larvae, ingested by a grooming host, or having fallen into an uninhabitable environment. Still, assuming a dog acquires 5 female fleas, and 25% of their eggs survive, within a month the infestation would grow to over 4,000 fleas.


How Many Eggs Females Lay

A female flea lays an average of 20-30 eggs a day, roughly an egg per hour. She’ll begin producing eggs 1-2 days after acquiring a host and consuming a blood meal.

Oviposition rates begin low, with 5-10 eggs produced on the second and third days of feeding. Production peaks 4-9 days after the first blood meal. At the peak, females can lay up to 46 eggs a day, but, in most cases, the maximum is 25-30 eggs per day. A high rate is sustained for 2-4 weeks before tapering off.

Adult Flea Lifespan

In natural settings, adult fleas live for around a week. They can survive for over 100 days in labs, but their lifespan gets significantly reduced due to host grooming. Within a week, cats will groom off or ingest around 50% of their fleas. They can kill 3-12 fleas per day.


A female’s lifespan determines the total number of eggs she can produce. Older studies thought average fecundity was close to 800 eggs. Newer research shows that an average female lays less than 200 eggs during her lifetime. Average fecundity can be estimated at close to 175 eggs, given that females live for an average of 7 days and produce 25 eggs a day.

Most Eggs don’t Reach Adulthood

Fertile vs Non-Viable Eggs

Many of the laid eggs will be non-viable and can’t develop. Only 30-46% of the eggs will be fertile, depending on how many times the female has mated.

Host Grooming

Fleas lay their eggs on the host animal, but they drop off within a few hours. However, before they fall, some of the eggs will likely be ingested by the host during grooming. The amount consumed may be as high as 27.7%.

Habitat & Food Requirements

Dislodged eggs drop into the environment. They continuously fall, getting distributed anywhere the infested host wanders. However, to survive and continue developing, the eggs must fall onto substrates with specific requirements. Viable habitats aren’t widespread around homes. Still, many eggs accumulate where pets habitually sleep, rest, or feed. These areas are typically well suited for development.

Flea eggs require a relative humidity (RH) between 50-92%. The ambient temperature must be between 50.4°F and 100.4°F (10°C and 38°C). And the larvae require dark, protected environments. They’ll avoid sunlight, moving toward shaded areas or burrowing beneath the surface.

Upon hatching, the larvae must have access to flea dirt and eggs for food. They’ll starve within 3 days without these nutritional components.


Flea larvae will feed on conspecific eggs, both fertile and non-viable. They may prefer non-viable eggs because of their flat, easy-to-grip shape. The larvae will also cannibalize younger or injured larvae. Late stage larvae may even eat pupae without full cocoons.

Host Availability

In homes, newly emerged adults must find a host and feed within a couple weeks or they’ll starve. To help ensure a host is around when they emerge, adults can remain quiescent inside their cocoons for up to 155 days. They’ll rapidly emerge once they detect an animal.

Flea Life Cycle

Cat fleas are holometabolic insects. They develop through four distinct phases: Egg, larva, pupa, and adult. Infestations consist of 50-57% eggs, 34-35% larvae, 8-10% pupae, and 1-5% adults. Discovering adult fleas on a pet is only seeing the “tip of the iceberg”. For every adult, there are around 100 immature stages hidden in the environment.

How quickly fleas develop depends upon temperature and humidity. In a home environment, the life cycle often completes in 17-26 days. Eggs hatch into larvae within 2-3 days. Larvae begin spinning a cocoon and pupating 7-11 days after hatching. The cocooned prepupae will pupate and reach adulthood in 7-19 days.

How Fast Fleas Reproduce

Fleas multiply quickly. Within a month, a single female will breed thousands of descendants, though most won’t reach adulthood.

Let’s put together the aforementioned factors, while simplifying a bit. Assume a dog acquires 5 female fleas. Each flea lays 25 eggs a day. Of those 125 daily eggs, 75% are either non-viable, cannibalized, consumed by the host, or fall into inhospitable environments. This leaves around 30 viable eggs per day. With an average life of 7 days, these 5 females will lay a total of 210 eggs that’ll eventually reach adulthood.

Now let’s assume it takes 20 days for the eggs to become adults, half being female. At day 20, 15 new females will emerge, jump onto the host, feed, mate, and begin laying a total of 90 viable eggs per day. At day 21, another 15 females will emerge and do the same. And so on. The population will grow exponentially. By day 30, the infestation would surpass 4,400 fleas.

The longer a flea problem goes undetected and untreated, the worse it’ll become and the harder it’ll be to control. Oftentimes pet owners don’t realize how bad an infestation truly is, because 95-99% of the fleas are hidden in carpets as eggs, larvae, and pupae.


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