According to this page, there are two general groups of cicadas in Alabama—the periodicals and the annuals. These are remnants of annuals. The next periodicals in northern Alabama will emerge in 2011. They’re on a 13-year cycle. (I thought there were only 17-year cycles, but there are 13-year ones too.)
I learned something else interesting today. Cicadas are on 13- and 17-year cycles because those are prime numbers. They therefore escape synchronization with the life cycles of predators, like praying mantises and cicada killers. If a cicada had a 15-year cycle, eventually it’d be consistently screwed with predators that have three- or five-year cycles, right? I thought that was nifty.
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I love those little shells. We used to make armies out of them, when we weren’t hanging them on our clothing.
I’m still trying to wrap my mind around the scenerio whereby natural selection produces a bug on prime number cycles. No luck yet.
We had a big bloom of cicadas on Cape Cod this year. Noisy little guys.
Hooray Prime Numbers!