There are multiple species and broods of periodical cicadas - they're literally called that - it's really quite an interesting phenomena, but they have evolved

There are multiple species and broods of periodical cicadas - they're literally called that - it's really quite an interesting phenomena, but they have evolved life cycles in that are prime numbered years long, and frequently relatively prime as well. The extended life cycle means that no predator can rely on a single brood, and the relatively prime brood lengths of different groups mean they don't overlap sufficiently frequently for predators to manage by feeding on different broods each year. Then on a year when they do emerge they emerge in colossal numbers, far more than you experience with annual cicadas, and there's also nowhere near enough predation to meaningfully dent their numbers. This years exciting horror is the result of a bunch of things, summarized from the University of Connecticut [https://cicadas.uconn.edu https://cicadas.uconn.edu]: * For the first time since 2015 a 13-year brood will emerge in the same year as a 17-year brood. * For the first time since 1998 adjacent 13-and 17-year broods will emerge in the same year. * For the first time since 1803 Brood XIX and XIII will co-emerge. This particular event won't be one of the all encompassing horrors though as apparently the range of the overlap is relatively small.