What is the shrill incessant noise that fills your backyard to such great lengths that you can't even hear your own thoughts? Cicadas are large homopterous insects with long transparent wings, found chiefly in warm countries. That noise you hear is the male cicada, who makes a loud, shrill droning noise by vibrating two membranes on its abdomen.
But the life cycle of Magicicada cicadas in North America is unique in that they spend 17 years underground feeding on sap from tree routes. When the time calls, millions of them will emerge simultaneously and morph into their adult bodies. The males make their infamous noise to attract females for mates. The females make a much quieter click with their wings. When a male finds a mate, his call alters - signifying that the 17 long years of abstinence has come to an end.
But how do the cicadas all know when to emerge? Scientists know that they can detect changes in the contents of tree sap, and hence recognize the passing of time. It's thought that this long life cycle may have evolved as an adaptation against predators such as the cicada killer wasp and praying mantis.