Cicadapalooza

Well, the cicadas finally started chirping today. For those not lucky enough to be living where they are flocking, we've got enough at our house to make up for it. We have this wooded area behind our house, and from about 6 a.m. to 6 p.m., all you can hear is the chirping. It's so loud that you can hear it inside the house with the TV on. Not to mention they keep latching on to the walls and trees and they're just disgusting to look at. I'm glad I won't be here to deal with the aftermath when all the shells are left behind. Exactly what purpose do these insects serve?