Adult fleas lay all of their eggs on the pet, but they soon fall off the animal and onto the carpet or furniture or clothes. Fleas' eggs develop into  larvae that remain deep in the carpet, under cushions, on furniture and other hospitable places in the home. The larvae feed on feces from the adult until they develop into pupae, encased in cocoons, that are resistant to insecticides. Because these cocoons are insecticide resistant, the pupae eventually develop into adults. That's why, even after a treatment, some adults are seen for some period after a treatment.
 
Habitat - Natural habitat for fleas include tall grasses, yards & fields. Pets are not the only way fleas are introduced to the interior of homes. They can ride in on womens' nylons and on pants legs.

Control - First, treat your pet's environment with an appropriate pest control product. That's where 90% of the developing flea population is located. If it's a dog house outside, thoroughly treat the doghouse and the immediate area. If the animal spends many hours indoors, then the home will have to be treated also. Listed on the right side panel is an array of very effective pest control products for fleas.