I remember reading an article (sorry don't remember where, but it might have been Scientific American), that asserted that the cycle periods of various Cicadas being prime (I guess that there are 7 and 11 year varieties), could be explained by trying to outlive predators -- the idea being to maximize the LCM of the predators lifespan with the Cicadas, so that there would be a large number of generations of predators between successive cicada generations, and there would be much less selective pressure for predators to specialize in cicadas (there wouldn't be much of a payoff). For a humorous look at cicadas (in Princeton we seem to have a local hot spot) see http://www.cicadaville.com/ -- Victor S. Miller | " ... Meanwhile, those of us who can compute can hardly victor@idaccr.org | be expected to keep writing papers saying 'I can do the CCR, Princeton, NJ | following useless calculation in 2 seconds', and indeed 08540 USA | what editor would publish them?" -- Oliver Atkin