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—appears only every 17 years. Yet some people saw Brood X in 2017. Researchers suspect that a warmer climate could be triggering the “periodical cicadas” of Brood X and others to emerge four years early. Watch to learn how periodical cicadas permanently altered their lifecycles in the past—and why it might happen again.

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