Cicadas

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The New Yorker has a short essay about long reproductive cycle of the Cicadas.  Cicadas emerge every 13, or 17 years; this year’s appear every 17 part of the largest “brood.”  13 and 17 are prime numbers.  The theory for why that is is that this helps them remain out of synch with the reproductive cycles of their predators.

This all reminded me of the mast years.  You’ll recall that mast years are apparently random events were in a given species of tree across a region will produce a vast number of seeds.  Animals that eat those seeds are overwhelmed so some of the seeds survive.  But also the animals suffer a population bubble, and the the following year they starve.  There is an amazing story about the ripple effects of a mast year in Bamboo.  In that story the rat population exploded, and the next year the rats moved onto eating people’s grain stores; which lead to a revolution.

Which got me wondering what are the ripple effects around the Circada’s emergence.   This essay provides a bit of of that.   The Circada laval eat tree roots – trees have very long reproduction cycles – and you can see the signature of the prime number cycles in the tree rings. Moles thrive in the year before the emergence as they feast on the soon to emerge population.  Presumably next year will be a lousy time to be a mole.

That article also talks about wasps and bacteria.   Settling into a reproductive cycle based on a prime number is only gone to help you avoid predators who’s reproductive cycles are multiples of years.   Moles, rats, and wasps for example.  But it’s no help against the bacteria.  They can ramp up their population fast.   Which leads to a curiosity that older trees have a resident population of bacteria that loves to eat Circada; and the Circada tend to emerge around younger trees.

Meanwhile there is a cool example of crowd sourced science over at MagiCicada.org, where you can see where they are emerging.  See also www.cicadamania.com.  Sadly they aren’t common here in Boston.

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