Billions and Billions of Periodical Cicadas
When soil temperatures 8 inches under the ground reach a balmy 64 degrees Fahrenheit, periodical cicadas emerge on the U.S. East Coast. They tend to do it in groups—whole regions containing billions of cicadas are synchronized in 17- or 13-year cycles. This year, Brood X is emerging after 17 years underground. Find out more about cicadas from the Encyclopedia of Life and see more images at Smithsonian Libraries.