As long as there is a host animal on which they can feed, such as a dog or cat, fleas will not die on their own and will require some action on your part in order to get rid of the infestation.
After a flea obtains a blood meal from a host animal, it can lay up to 20 eggs per day directly on the body of the host, so a flea infestation can quickly multiply and get out of hand.
You will need to get any cats and dogs in your home on flea medication such as Frontline, and you may also combine that with other flea control products in order to increase effectiveness.
Even if you don’t have any pets in your home, flea pupa are encased in a silken cocoon and can lie dormant for many months, only to emerge as adult fleas when they detect the presence of a host.
So even though it may seem like the fleas are gone, they did not die but instead have only gone dormant for a period of time.