Lesson 2: Biology of the Flea

The Flea Life Cycle

Learn it, know it, live it. There are four life stages of the flea and it is important to know how to break this life cycle in more than one place. (This two step approach provides the most rapid control and the least resistance to flea control agents in future flea generations.)


At any given time about one third of the flea population in someone’s home is present in the egg stage.  The adult female flea lays up to 40 eggs daily. The eggs are laid on the host where they fall off to hatch in the environment.  Eggs incubate best in high humidity and temperatures of 65-80 degrees.


At any given time about 57% of the fleas in someone’s home are in the larval stage.  Larvae are like little caterpillars crawling around grazing on the flea dirt that is generally in their vicinity. (Flea eggs and flea dirt both fall off the host. When the eggs hatch, there is a bounty of food prepared lovingly by all the host’s fleas waiting for them).  This is the stage that picks up tapeworm eggs (also likely to be in the vicinity) as they graze.

As they get to a certain age and size, a molt occurs.  The first larval stage is called the first “instar.” After the first molt, the larva becomes the second “instar.”  After the third molt, the larva is called a “third instar larva” and is capable of spinning a cocoon and pupating.

The time between hatching and pupating (ie the time spent in the larval stage) depends on environmental conditions. It can be as short as 9 days.

Note: Larvae are killed at 95 degrees. This means that they must live in some area where they are protected from Summer heat. This means the shade of the yard or indoors.


By this life stage most young fleas have been killed off by an assortment of environmental factors.  Only 8% make it to the pupal stage but once they have spun cocoons they are nearly invincible.  The cocoon is sticky and readily picks up dust and dirt. Inside the developing cocoon, the pupa is turning into the flea that we are familiar with. They are especially protected under carpet, which is why carpet has developed such a reputation as a shelter for fleas.

The pupa can remain dormant in its cocoon for many months, maybe even up to a year as it waits for the right time to emerge.


After the pupa develops, it does not automatically emerge from its cocoon. Instead, it is able to remain in the cocoon until it detects a nearby host. The mature pupa is able to detect the vibrations of an approaching host, carbon dioxide gradients, and sound and light patterns.  When the mature pupa feels the time is right, he emerges from the cocoon, hungry and eager to find a host.

A common scenario occurs when a dog is boarded while the owner is on vacation. The owner picks up the dog from the boarding kennel and returns home. The mature pupae have been waiting for a host and when the dog enters the home, a huge number of adult fleas emerge at once and attack the dog creating a sudden heavy infestation. Often the boarding kennel is blamed for giving the dog fleas. What really happened was that the pupae waited to emerge while there was no host present and then all emerged suddenly when the host arrived.

The unfed flea is able to live for months without a blood meal but during that time it is aggressively using all its powers to locate a host. Once it finds a host, it will never purposely leave the host.


After the adult flea finds a host and takes its first blood meal, metabolic changes occur that alter the flea forever.  The flea is now called a “fed flea” and, if separated from its host, will die in only a few weeks without a blood meal.  The female flea begins to produce eggs within 24-48 hours of her first blood meal and will lay eggs continually until she dies.

The average life span of the adult flea is 4-6 weeks, depending on the grooming abilities of the host.


A Few Words on the Common Tapeworm

There are many species of tapeworm but the one most of us are familiar with is the Common Tapeworm, Dipylidium caninum.  You should be familiar with this species and its life cycle.

Be sure you have read the tapeworm page on the hospital web site and are familiar with its biology. To get to this page click here.

Last updated: August 31, 2002