These cicadas count to 13 or 17 years before they ever see daylight

Magicicada nymphs spend 13 or 17 years underground feeding on root sap before emerging together by the billions in a single synchronized month. Both cycle lengths are prime numbers, which mathematically minimizes how often a brood's emergence year lines up with the multi-year cycles of predators, making it far harder for any predator to specialize in eating them.

— Jin Yoshimura, The Evolutionary Origins of Periodical Cicadas During Ice Ages — The American Naturalist, Vol. 149, No. 1, 1997