I forgot and left a bag of fruit in my car. When I found it a few days later, it was covered with fruit flies. But the car doors were closed, and the windows were shut tight. How did they get in?

—Glenn Robinson, Cleveland, Ohio In your heart of hearts, Glenn, you know the answer, don’t you? They were already on the fruit as eggs or larvae, otherwise known as maggots. Ugh. But if you had said the flies appeared on the fruit in your kitchen, we wouldn’t have known the awful truth for sure. That’s because the flies are so tiny that they can easily get into homes as adults through windows or screens. Or you can bring them home as eggs or larvae right from the grocery store.