The upper bound could be because it’s a long time to live as a glorified grub. It’s also interesting that the different periodical broods have pretty distinct

The upper bound could be because it’s a long time to live as a glorified grub. It’s also interesting that the different periodical broods have pretty distinct boundaries: https://en.m.wikipedia.org/wiki/Periodical_cicadas#Map_of_brood_locations https://en.m.wikipedia.org/wiki/Periodical_cicadas#Map_of_br... Perhaps the same selective pressures that separated the broods geographically also filtered out shorter cycles due to predation?