06 April 2008

The Cicadas are Coming!

The group of Magicicada known as Brood XIV is coming out in Massachusetts and other parts of the Northeast this year in April or May. According to Wikipedia, they will be seen in parts of Ohio, Kentucky, Tennessee, Massachusetts, Maryland, North Carolina, Pennsylvania, Virginia, West Virginia, New York, and New Jersey.

The last time I remember cicadas being in the news was the emergence of Brood X in 2004.

Magicicada come in varieties that come out (to mate) once only every 13 or 17 years. They are divided into 30 broods based on what year they come out. Broods I-XVII are 17-year cicadas and XVIII-XXX are 13-year cicadas.

Scientists theorize that having a life cycle that is a large prime number of years long helps the cicadas to escape predators or parasites. Predators that come out every year would alternately have to lie low for 16 years and be completely overwhelmed by cicadas on the 17th. And predators with any period of between 2 and 16 years would have to wait 17 cycles (34 to 272 years), because 17 is relatively prime to all numbers between 2 and 16. Either way, not a great niche to be in if you're a predator. (The same numerical reason prevents 13- and 17-year cicadas from interbreeding too much and creating intermediate forms.)

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