If you live in a Southern state, you might have heard stories about the 13-year-cycle cicadas emerging this year for the first time since, well, 1998.  They’ll pop out of the ground, fully grown, sing super loud, find mates, breed, and lay eggs.  Then the babies will burrow into the ground and there’ll be no more of those cicadas for the next 13 years.  There are also some 17-year-cycle cicadas.

But why do they cycle in such big prime numbers?  It’s the best defense against predators.

Let’s say most of the predators who feed on cicadas have 2-5 year cycles.  If the cicadas also had such cycles, everytime the little bugs came out to mate, they’d be wiped out by the masses of predators on the same timeclock.  And if the cicadas were on a larger cycle that was divisible by a smaller number (say a 10 year cycle), everytime they came out to breed, there’d be a mass of predators on a 5 year or 2 year cycle to wipe them out again.  But to get a 13 year cycle to sync up with a 5 year cycle means the cicadas would only be feasted upon every 65 years, giving them over six decades in between to rebuild their numbers.

And there’s your science lesson for the day.

3:17 pm  •  19 May 2011  •   Let's talk about what you think.
| cicadas| the south| insects| nature| science|