There are over 2,000 flea species in the United States, but the most common home-invading flea is the cat flea (Ctenocephalides felis). These tiny parasites rely on the blood of animals, with a preference for animals over humans. Warm-blooded mammals like cats, dogs, humans, deer, and even pests like mice or rats are shared hosts for fleas. They enter homes when their hosts come inside. Flea infestations can quickly escalate, as female fleas can produce over a thousand eggs in their lifetime.