Maximilian Wilson wrote: >You're probably aware of this already: the cicada has a 17-year cycle. >http://www.gardenersnet.com/atoz/cicada.htm > >-Max > > > Only some of them. Some have 13 years, some 7, etc. Some subtle mathematics combine with evolution to favor odd-year cycles, but not necessarily of 17 years only. Snarkhunter