How do flies appear to spawn from rotten food in a seemingly closed, flyless environment?

Question

I haven’t had a fly for months in my apartment, I never really have any. But if I leave food to rot somewhere, there are gonna be dozens of flies overnight. Not fully grown, but a lot. All windows are closed and I’m not sure where, biologically, they’re coming from.

In: Biology

Answer 1

Fruit flies can lay hundreds of eggs. They may take a week to hatch. Then BOOM, they’re everywhere. Could come from some old banana u left lying around.