People often move into a house or unit and find that they are covered in fleas. Why? A flea treatment can kill the adult fleas, but do nothing to the eggs. There are limited treatments that will affect flea eggs. The best thing to do is return after the initial treatment to make sure that the hatched fleas are killed too. What happens is when people walk in and cause vibrations this actually hatches the pupae out into an adult. As it comes out it is fighting fit and looking for its first feed of blood. This is why it feels like there are heaps, but it is actually because they are so aggressive at first. This reduces after the feed, but who wants it.