Most butterflies lay eggs in spring, before the approach of the summer months. So caterpillars generally turn into butterflies in the months of April and May. But that is not always the case.  Some butterflies also lay eggs in the colder months. The newly-hatched caterpillars don't even take time to eat. They enter a form of hibernation and burrow into the soil to stay alive until spring. They turn into butterflies in early spring.