Cool Tech: Cicadas in their Prime

This year there will be a massive swarm of cicadas in the Chicago area. I remember cicadas from when I was a kid. After they moulted they'd leave a cool hollow bug shell on the trees all over our yard. You could hear them all night every night over summer, and it's a sound I was so used to that I can sometimes still "hear" it at night when I am drifting off.

Cicadas live on extremely long lifestyles. They spend 99% of their life digging around underground sucking on the roots of trees, before burrowing up one summer, growing wings, and participating in a massive orgy of sex and singing for a few brief weeks before spawning the next generation and dying.

Cicadas have differing cycles depending on the many breeds, but check this out: all cicadas live for a prime number of years. The number depends on species, including 7, 13, and (including the coming local swarm) 17. Nobody knows why, but there's no 11-year cicadas.

So are these cicadas just cool geek types, or is it a coincidence, or what? There are differing theories. Some think they developed it as a survival mechanism to avoid predators. By picking a long prime cycle, they decrease the chance of synergy with cycling predators. For instance, if they'd picked 15 instead of 17, a predator could feast on them by being particularly active every 3 or 5 years.

Another possibility is that they do it to avoid other cicada breeds. If there are 13-year cicadas and 17-year cicadas active in an area, they can avoid running into each other except every 221 years. At which point, presumably, it's insect armageddon!

A time lapse of a cicada moulting.