Cicadas: Cicadian Rhythms

Summer in Japan is always associated with semi, or in English, the cicada. They provide the soundtrack of summer, with the males chirping incessantly to attract a mate. Some species hit 120 decibels, equivalent to standing in the front row of an AC/DC concert.

Cicada nymphs spend years below ground and emerge when the soil temperature gets warm enough, molting in the process, leaving a vacant shell behind. Because of their apparent ability to reborn, cicadas have come to represent resurrection and immortality in many cultures. In Taoism, they are symbols of tsien, the soul that leaves the body at death.

Fun fact: some species of cicada match their yearly life cycles to prime numbers. The reason for this mathematical precision is to avoid even-numbered and therefore predictable breeding cycles, which their predators could match. By ensuring that trillions hatch on a single evening, but at unpredictable times, they literally swamp their predators who gorge themselves until they can’t face anymore, without damaging the cicada population. The 13- and 17-year cycles only coincide once every 221 years.


Ghost in the shell?