This year, billions of cicadas descended on the eastern United States. Unlike other groups of the insects, which show up on a yearly basis, this year’s crop—known as Brood X—only appears every 17 years. Yet some people saw Brood X in 2017. Researchers suspect a warmer climate could be triggering the “periodical cicadas” of Brood X and others to emerge 4 years early. Watch to learn how periodical cicadas permanently altered their life cycles in the past—and why it might happen again.