Re: Noisy little buggers...
Yes, there is an explanation why their cycle is 17 years. It is something like this (cant remember the details):
cicadas had a short cycle of 1 years, and their predators too. Then cicadas switched to 2 years, and the predators who had a cycle of 1 year, adapted. Then cicadas switched to 3 years, and the predators too. The cicadas could not switch to 4 years, because that is 2*2 years which the predators could handle (they knew how to handle 2 year cycles). So the cicadas tried prime number long cycles, because non primes could the predators handle. Finally, when the cicadas switched to 17 years, the predators had to try every combination (2 years, 3 years, 4 years, etc) but the cycle when they meet was far too long so the predators died out.
It has to do with least common divisor. When you try to find a cycle of 2,3,5 years it is doable, but it takes time. But when you go to 17 years, the predators will meet the cicadas once in every 217 year (or so) which the predators could not handle. So they died out of starvation.
It is described in the book "Fermats last theorem" by Simon Singh.