My colleague Mike Dryden, who has spent his career studying fleas on pets, has a very informative YouTube video called, The Dirt on Fleas. The video outlines a basic strategy for minimizing flea problems.
When fleas on a pet become noticeable, there will be many fleas in the pet’s environment. Fleas on a pet begin to lay eggs 24 h after they begin feeding. Fleas lay 30 or more eggs per day which drop off the pet and are distributed in the environment. A noticeable flea infestation on a pet will have already produced thousands of flea eggs. The eggs hatch into larvae that develop in carpet, cracks and crevices or in shady areas of a yard. Depending on conditions a flea takes 3 to 8 weeks to go through its larva and pupa stages and become an adult. This means that if a pet has a noticeable flea infestation, immature fleas in the areas that the pet visits will be reinfesting the pet for the next 3 to 8 weeks. It is difficult to eliminate fleas from the environment. However, if a pet is treated as directed with a product that kills fleas before they lay eggs, no new eggs will be produced on that pet. If there are other pets, all must be treated for fleas to prevent egg production. With no new eggs being produced, all the eggs will disappear from the environment after the ones already present hatch. With no new larvae hatching, the larvae disappear after they all turn into pupae. the pupae disappear after they all turn into adults. Throughout this period, the adult fleas try to feed on the pet, but are killed by the flea treatment. Eventually all the fleas will be gone from the environment.
A new infestation can start at any time with fleas from stray dogs and cats or from feral animals (raccoons, opossums) that roam outdoors. A prophylactic flea treatment will kill new fleas before they can reproduce and prevent another flea infestation.