Every 17 years something astonishing happens. Large, red-eyed cicadas emerge by the trillions and begin flying clumsily through the humid air. Depending on where you live, this could be your summer to tread carefully, cover your ears and act like you’re not really afraid of the burgeoning brood. But that massive cicada infestation is not the astonishing part. What boggles the mind is their timing and the way cicadas coincide with world-changing events.  Ancient civilizations understood this prophetic power. They referred to the broods as “locusts,” and their arrival was viewed as the portent of something cataclysmic: from floods and famine to wars and baby booms. That thinking may seem archaic and even humorous