[Dragaera] [SKZB] 17-year cicada

[Philip Hart]

On Fri, 4 Apr 2008, Ken Koester wrote:

> 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.

I learned prime number cycles were selected for, though a quick google
suggests this is still controversial.  The basic idea is that it would
be hard for a predator species (which presumably can't go into cold
sleep for n years and wouldn't otherwise have such a long population 
cycle) to sync with the cicadas.

Other interesting related stuff:
http://links.jstor.org/sici?sici=0014-3820%28200302%2957%3A2%3C428%3AACOGIV%3E2.0.CO%3B2-1&size=LARGE&origin=JSTOR-enlargePage
- the basic idea being that prime-cycle cicadas won't mix genes with
cicadas of other length cycles and get their periodicity muddled, ruining
the whole effect of avoiding synching.