Pests & Prime Numbers?

Summer brings around lots of fun memories: time at the pool, hanging out with friends, going to the beach. But every thirteen years here in Central Georgia, you can add one more thing to that list. The incessant buzzing of the cicada, a small insect that rears its head in large masses every 13 years. At least we have one more year before the fun begins. The cicadas aren't due to arrive until July and August 2011.

The Day After Tomorrow

But why is it exactly 13 years in-between outbreaks? And why 17 years for their cousins up in New England? While scientists aren't 100% sure, it appears to relate to math. Yes, math. See, both 13 and 17 are prime numbers, numbers that are only divisible by one and itself. It's believed that cicadas only arrive in prime number patterns to avoid predators. Cicadas are small insects that are very low on the food chain and have many natural predators. By appearing so sporadically, they can avoid most of them. Think about it, if cicadas appeared every 12 years instead of 13, they would also have to deal with predators who come around either every 2, 3, 4 or 6 years. There's a high probability that the cicadas would be wiped out. Add just one year and the probability plummets. The odds of running into a predator that comes around every 4 years is 1 in 52, or less than 2%.

So the next time you're sitting in math class (or listening to your child complain about math class) and you wonder, "Why would I ever need to know this?", remember that even the smallest parts of our world, like cicadas, rely on math and its applications to survive.