Flea infestations often come from a pet dog or cat. The pests attach to the animal when it’s outside, and then infest its fur and the places it sleeps indoors. Flea prevention for both the home and yard can be difficult. Fleas depend on a blood meal from a host to survive. On some occasions, fleas may become an inside problem when the host they previously fed on is no longer around. Then fleas focus their feeding activity on other hosts that reside inside the home. 

Dog flea (Ctenocephalides canis) on white fur. Microscopic photo