Ever wonder why we have so many flies? These two are probably a few days old. Their life cycle is brief but productive. Within minutes or hours after this female’s eggs are fertilized, she’ll find some nice smelly garbage or manure and bury her eggs, from 150 to 500. In four or five days, the eggs will hatch into maggots that will squirm and eat their way through their food supply for about five days. Next they’ll go into hard cases called pupa for another four days before hatching into adult flies. A day or two later they’ll find mates and get busy making more flies. Total time between generations? Roughly fifteen days.