Why do cicadas come out every 17 years?

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This spring, trillions of periodical cicadas are emerging from the ground, where they’ve spent 13 or 17 years feeding on xylem (basically, tree juice).  The two specific broods emerging this year have not come out at the same time since 1803, and kids may be hearing a lot of news about these loud insects. So today we’re tackling the cicada questions you’ve sent us: Why do cicadas come out every 17 years? What do cicadas eat? Why are there more cicadas at night than in the morning? Why do cicadas molt? How do cicadas get babies? We speak with Dan Gruner, professor of entomology at the University of Maryland, to get answers. Download our learning guides: PDF | Google Slide | Transcript