Flea eggs hatch into worm-like larvae which move away from light and downwards. This means that they are usually found deep in the carpet pile. They tend to accumulate in areas where the pet rests, but have been observed to crawl as far as 20 feet while in this stage of the life cycle.
 

The lessons for effective flea control are:
 

1. Whilst household sprays can certainly help, it can be difficult to be sure that you've treated all the hard-to-get areas that flea larvae congregate.
 

2. Flea prevention is better than cure. In other words, far better to treat your pet before it catches fleas, than end up chasing possibly hundreds or thousands of flea larvae around the house.