As soon as ladybugs hatch, they begin to feast. Once hatched, the larvae eat about 350 to 400 aphids in the two weeks it takes them to become fully grown. They consume about 5,000 Ahids in their lifetime. Aphids are more than just a food source, however; they also work as a signal for when it's time for ladybugs to mate. When the aphids begin to disappear, ladybugs realize that winter is coming and flock to ancestral homes that they've been to before for a once-in-a-lifetime-event of mating right before entering hibernation.

-Treehugger.com