Cicadas in the US are unique. Scientists don't quite know why.
Trillions of cicadas that have been maturing underground for 17 years are starting to emerge in the eastern US. Enormous broods of cicadas that come out on periodic cycles, like this one, are "as unique to the US as giraffes are to Africa," says one scientist. The World’s Anna Kusmer reports that the science is not settled as to why the US is so special.