Tuesday, May 6, 2008

Seventeen Year Cicadas

It has been twelve years since our local brood of seventeen year cicadas crawled up out of the ground and flew in dizzy rapture to the treetops.

For a few weeks the air was filled with a buzzing, bewildering mob of giant insects. Individually they were defenseless, but there were so many of them that the predators gorged themselves and left them alone.

Five years from now, their offspring will do it all over again. How does a bug count to seventeen? And why seventeen? Apparently, scientists don’t really know the answer. Link

Tomorrow: Art By Committee

9 comments:

Arco Scheepen said...

First of all: great drawings!
I have somewhere read that the 13 and 17 years cycles are good for these animals because they're prime numbers, and thus unlikely to coincide with the cycles of their predators.

marionros said...

Pardon me to differ, but according to the link you provided, scientists do know how the chicadas count to seventeen. As for the why, that is a rather pointless question. You might as well ask 'why does it take twelve years for a human child to grow to puberty', or 'why exactly nine months for human gestation. How does a foetus count to nine. How does it *know*?! Is there something mysterious and mystical about the number nine?'
Nope, nothing mystical. It's just how things work. Some insect's lifecycle takes hours, others years. That's how they evolved, and it works that way because if it stopped working for them, they would die out and something else would take over their niche.
Sorry to sound grumpy, but I've just had to listen to a religeous friend of mine waxing mystical over the beauty of a butterfly and it's design 'revealed the existence of God'. Personally, I'm just as impressed with the design (evolutionary design that is) of a cockroach or the larvae of some parasitical wasp that eats its host while its still alive. Just because something is pretty to our human eyes, or because some number is mystical according to our culture doesn't mean that you can project meaning and purpose on nature! It would be like seeing a face in some rockformation on Mars or the face of Jesus on some mouldstain in the fridge. The human brain evolved in a world where seeing patterns even where there were no patterns were of use to him, after all.
So why does it take a 17 year chicada seventeen years to mature from larvae to adult chicada? Because it works that way for the chicada. And scientist have no problems finding out how this works. To ask 'why' is to assume there is a 'higher meaning' or 'purpose' to the world, and you could do that, but it would only give you the same answer over and over ("why? Because God wanted it so") and doesn't really explain anything at all. I'll stick with the scientist's 'how', if you don't mind :-)

James Gurney said...

Arco, the number 17 also struck me because it is a fairly large and unusual prime number. Wikipedia's explanation suggests as you say that it would allow them to fall out of step with predators with a 3 to 5 year cycle. But since the size of the brood overwhelms predators anyway, there might be another reason.

Marionros, I don't think asking why is a pointless question. Wondering the cause of things is at the root of any inquiry, especially a scientific one. And from this link at least the scientific explanation seems hardly settled. Dr. Marshall himself admits that "We don't know yet," and the explanation of the xylem flow and hormonal changes may account for part of the mechanism, but there must be a lot more to the biological clock.

Carol H. said...

Wonderful drawing! it brings back memories of living in Chicago and going out to a certain neighborhood that was completely covered by cicadas--I couldn't walk without stepping on them, and when I stood still they started climbing up my legs. I still have a couple of shells laying around here somewhere.

And when I was a little kid, one of the scariest things I can remember was hearing a loud buzz and seeing one of those things with their giant red eyes fly past -- it was as big as a dinosaur to me and that image stayed in my head for years.

fuuringo said...

Hi Mr Gurney,
I just want to drop a note to thank you for sharing your insights in this blog.
It must have been over 10 years ago that I discovered Dinotopia among the Children section books at my school library. I couldn't have been much older than those elementary school children you have been talking to are now.
It's a long time ago but I remember being fascinated with the world you had created, everything seemed real. For some reason I have a particular vivid memory of a dinosaur resting divan you had designed. I can now appreciate the effort involved in crafting that world.

A few years ago I started drawing "manga" and at the moment I'm looking for ways to improve by studying traditional methods. Reading your posts about studies from life have helped me open my eyes just a little bit wider and I hope to be able to approach art with a new frame of mind.

It's a strange feeling to have read your book as as a child and now be posting on your blog ten years later, the internet is fantastic.

Thanks again,
Nana

bajel said...

awesome blog! thanks

Joe Sutphin said...

Eh...not too big on bitter ranting when i come to an incredible art blog.
but i will say that i have always had absolute respect for any creature that can survive 17 years in the ground. as a teen i once stopped a little kid from stamping on a locust at a birthday party that had just emerged and was going to become a Cicada. i explained to that kid that this 'ugly' bug that he wanted to squash was as old as he was, and that he wouldnt want someone to just smash him. it seemed to give him new sight on the matter. about 6 years ago our 17 year cicadas came out in Central Ohio and our news reporters did their reports from the parks, just stomping all over them to point one out on a tree. i too went to the parks just to see them all, and i tip-toed as best i could while observing:)
thanks for the great sketch and inspiration Jim...and as for the "why?" thats what makes it fun to talk about. so in my opinion, keep asking why.

Erik Bongers said...

I love the 'why' debate.
I think 'why' shoud be seen in perspective. There are many diffent sorts of why.
I agree with James Gurney that the scientific 'why' is fascinating.
But I also agree with Marionros that the more metaphysical 'why' leads to pointless debates as all of these just reflect subjective (that is 'unprovable') opinion.

For me, I believe the scientific 'why' is a perpetual question. With every answer you find you automatically get a new question.

True, the scientific 'why' isn't a very 'deep' why - it's more a mechanical why : why do we live? Because our hearts beat? Because we evolved from single-cell organisms? Because they evolved from complex proteins? Sure, sure, but that's just a 'mechanical' why.
It's not a real 'why' is it. That is, it doesn't explain if there is a 'purpose' to all of this.
A devine purpose? A to use mortals unconceivable purpose? Or no purpose at all?

I've learned to live with the believe that it's pointless in trying to find a real 'why', and I'm happy to stick with the very narrow (but nevertheless very fascinating) scientific and perpetual why.

Shawn Escott said...

Wow, that is amazing! Those little guys have been programmed to do what they were meant to do, in just the right time. Amazing drawings too!