As already said, this springs will bring swarms of cicadas to U.S. East Coast, from North Carolina up to Connecticut. Yet, it's a mistery how cicadas got stuck in 13 and 17 year life cycle.
Cicadas spend most of their living time underground, by surviving on bacteria and tree roots. When the ground reaches 18 °C, in the 13th or 17th year ( depending on their species), they leave their colonies to search for a mate.