The reproductive cycle of fruit flies is approx 10 days. A single fertilized female will lay 100s of eggs over her life. But not all at once, it's more like 5 a

The reproductive cycle of fruit flies is approx 10 days. A single fertilized female will lay 100s of eggs over her life. But not all at once, it's more like 5 a day. So if you have a single fertilized female in a room, about 10 days later, you will start getting those handful flies emerge every day. You can keep your room completely isolated, but still you can catch 5 a day on average for about a month or two (in lab conditions longer). If you don't catch them all and you end up with another fertilized female, the story continues. I think flies are very opportunistic individuals, in the sense that there is always a fly hatching somewhere. If there is food, it will lay the eggs there. If there is no food it will try and stick around or die. But even if it dies, it's bothers and sisters are constantly emerging. So the population will survive a lot of adverse conditions.