A recent article puts to rest the question of what happens to flees when they are vacuumed up!
Experiments conducted by Ohio State University researchers on the cat flea (Ctenocephalides felis)—the most common type of flee plaguing companion animals, such as dogs and cats, and humans—showed that vacuuming killed fleas in all stages of life.
The stages of life of a flee aren't very appetizing: Fleas have multiple life stages- Adults suck the blood of their host and females lay eggs on them. The eggs roll off onto the floor, furniture or pet bedding and hatch two to 14 days later. The insects go through three larval stages, the last of which spins into a cocoon to protect the pupa stage. New adults typically emerge within a week or two.
Click the link below for the full study, but the good news is, when it comes to flees, a vacuum really sucks!!!