In their prime: how trillions of cicadas pop up right on time

Right now, across much of the midwestern and eastern US, trillions
of cicadas are crawling out from the soil. And this year is extra
special, because two broods are erupting from the ground at once.
The first brood hasn’t been seen for 13 years, the other for 17
years and the last time they emerged together Thomas Jefferson was
president. Ian Sample speaks to entomologist Dr Gene Kritsky to
find out what’s going on, why periodical cicadas emerge in cycles
of prime numbers and how they keep time underground. Help support
our independent journalism at theguardian.com/sciencepod