Here in the Northeast, screens are REQUIRED. To keep out flies, mosquitoes (doesn't always work); and other insects. When you buy or sell a house, you make certain there are screens for each window. If you rent an apartment, the only way the landlord can get the occupancy permit which allows the rental is if there are screens on all windows.

I know other parts of the country do not need screens.

And I've always wondered, don't birds just fly in if you don't have screens?

So: do you have screens where you live?