Joe Ganley [http://ganley.org/]

Writing code since 1979

I have been a professional software engineer for over 10 years. I have written many kinds of software, but my particular strengths are interactive graphics applications, compilers and interpreters, and algorithms.

I also enjoy writing, woodworking, and home improvement. Also this.

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Monday, May 03, 2004

Where I live, we're due for the emergence of 17-year cicadas this year, featuring swarms "of biblical proportions," as in hundreds of insects per square foot. There is a great article in today's Washington Post about cicadas, which answered several questions I've always had about them:

It is important that they emerge simultaneously because their only defense mechanism is their sheer numbers. Other cicadas with shorter cycles have evolved other defense mechanisms, such as camouflage or speed, but the long-cycle cicadas rely simply on producing more cicadas than their predators can possibly eat.

The successful cycles are prime (13 and 17 are two of the biggest) so as to minimize the frequency with which multiple cycles emerge in the same year. Simultaneity is undesirable because the mongrel offspring of cicadas with different cycles will have cycles somewhere between their parents. This will reduce the number who emerge in sync with the next brood, thus reducing the defense mechanism mentioned above.

The successful cycles are long because this makes them more robust against emerging during a summer too cold to successfully reproduce (this was apparently common in the Pleistocene when these things evolved).

It is believed that the larvae time their emergence by counting the flowering cycles of the trees to whose roots they are attached.

The only of my questions that they didn't answer is, if longer cycles are better, why aren't there 23-year cicadas, or 29-year, or 37-year, or whatever? Cathy thinks 17 might just be the limit of their lifespan, just as the limit of humans' lifespan is 120 or so. Monte carlo optimization (such as evolution by natural selection) produces some strange solutions, doesn't it? I mean, sure, staying near-dormant underground for 99.8% of your life is great for survival, but how much fun is it?

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