Fleas only spend about 5% of their life cycle on your pet. Treating the environment, where possible, can help prevent parasites from even making it onto your pet. "Flea Destroyer" nematodes work by releasing bacteria that kill the larvae, ending the flea life cycle without harming beneficial insects such as ladybugs, lacewings and praying mantis, as well as earthworms. They are safe for people, pets and plants.One box covers up to 2,000 square feet, and just one application can last a whole year