Flea life cycle

Fleas and butterflies have the same life cycle: adult, egg, caterpillar, cocoon, adult.

Adult flea emerges from cocoon full-sized and ready to go.

The newly emerged flea will leap at any likely source of warmth and vibration.  Although fleas greatly prefer the flavor of dogs and cats, they will settle for your ankle.

flea eggs and egg tooth (inset)

Once on the host, the female flea takes two or three blood meals a day and soon begins laying eggs . . .  about 150 to 300 eggs per week.  Seen with the naked eye, flea eggs look like large grains of salt. 

When ready to hatch, baby fleas use their tiny egg tooth to cut their way out of the eggshell.  Program keeps fleas from hatching by preventing development of this egg tooth

emerging flea caterpillar

This is your carpet, Mrs. Jones.
mature flea caterpillar, flea feces, eggs

The female flea sucks much more blood than she needs for herself, processing nearly all of it into nutrient-rich fecal pellets for her babies to eat. The baby caterpillars crawl around in your carpet or lawn eating whatever they can find, including cookie crumbs, miscellaneous organic matter, and these nourishing little fecal pellets.  (See dark fecal pellets in photo above, on the carpeting and inside the caterpillar.)

flea cocoons and pupa (inset)

When full grown, the flea caterpillar makes a little cocoon, just like butterflies do. Protected by this cocoon, the flea is impervious to insecticides and can wait many weeks for a host to come near.  When the flea senses vibration from footsteps, it pops out, looks around and immediately takes a leap. You can spray that rug all you want, but fleas will continue to emerge from their cocoons and nailing you on the ankle for about three weeks.  

photo source material courtesy of Novartis, manufacturer of Program™ for flea control and Sentinel™ for flea and heartworm control.