Magicicada septendecim is a cicada, a harmless and rather nondescript insect that grows up to 2 inches long. It might be truly nondescript if it was not what is called a "periodical cicada". This means that the life-cycles of these little creatures are synchronized; put another way, they become adults at about the same time.
(Imagine all humans -- all 6 billion of us -- going through puberty in the year 2006).
This is surprising enough. But there's something even more astonishing about this insect. They have very long life-cycles. How long? Try 17 years. Every 17 years, these cicadas emerge from under the ground in North America in huge clouds, fly around, find mates, lay eggs, and then die: all in a matter of weeks. Then they are gone for another 17 years. In the intervening years, you will find no adult Magicicadas.
Why such a long life-cycle? But more intriguing, is there any significance to that number 17?
(Hint: a cousin, Magicicada tredecim, has a life-cycle of 13 years. Why 13? Why 17?)
Any speculation welcome -- except if you've read Simon Singh's Fermat's Last Theorem, or have heard about this from somewhere else. Let's hear the speculation first.