Fleas become a pest when they get into our houses. Fleas in houses are usually linked with a pet or a visiting cat or dog. Flea problems often occur when the host animal has been absent for a period of time, such as when the family goes on vacation, taking the pet with them or boarding the pet for the duration of the vacation. Fleas may also be driven into the house during prolonged periods of wet weather. Each species of flea has one or two kinds of animals it prefers, although when hungry, it will attack a wide variety of warm-blooded animals, including humans.
Cat and dog fleas periodically jump on and off the host. When the host is removed for a period of time, they are left without food. Hungry adult fleas often attack on the first warm-blooded animal that comes in the door, often biting people around the ankles. In addition, vibrations promote the emergence of new adult fleas from pupae; walking across the floor will trigger emergence.
Sometimes flea treatments appear to be ineffective as small black fleas are seen after the treatment. This is because the pupae are quite resistant to chemicals. Fleas continue to hatch because flea treatment products cannot penetrate the flea pupa case. However once the adult fleas do hatch out from their pupa case they will land on the treatment and die.
You can better understand how a flea treatment will address your flea problem if you have a better understanding of how fleas behave.