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Periodical cicada/ 17- year cicada
2008-03-12
I think you can see many cicadas in the summer.But the cicada which, I'm just going to tell you, is quite different from annual cicada. I encountered with them in 2004. Those cicadas were an abnormal number, anyway!
If you hated any insects, you would pass out when you saw them, I guess.
Periodical Cicada
Molting/せみぬーど
They live underground almost of their life as nymphs and then they appear on the ground once every 17 years. The emergence is at about the same time.
According to Wikipedia, sometimes more than 1.5 million individuals appear.
Besides, there is a genus called 13-year cicada.
13, 17....
If the numbers bring you something to hit upon, you are sharp at mathematics.
As you know these numbers are prime number.
＊Prime number/素数＊
a number that can be divided exactly only by itself and 1, for exsample 7, 17 and 41.
Why they need to have such a period?
It is said that there used to be another periodical cicadas, too in the past, for example 3-year, 6-year and so on. But their period to emerge was so short and easy to concentrate that they couldn't survive , because of the luck of food or fight together.
Only the species have remained which have a period of emergence that it doesn't clash with the other's.
I and Miso-chan went out to gather their shells. She got many shells and brought them to Japan. I wonder if she has them still now.
17- years cicadas /Sorry for the creepy picture!
17と13の最小公倍数は221。すなわち221年に一度、17年蝉と13年蝉とが同時に大発生すると...。どんな感じになるんでしょうね？
ちなみに辞書によると、
最小公倍数... lowest(least) common multiple
最大公約数... greatest common measure
＊About periodical cicada
リンク先の下の方にある画像に注目！そんなさわやかに蝉を食べるなあぁぁ!!ホントにyummyなのか!?
http://biology.clc.uc.edu/steincarter/cicadas.htm
Periodical cicada/ 17- year cicada の続きを読む
