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The Rationale Behind the Cicadas' Swarm

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Millions of cicadas will likely invade the Chicago area in the next few weeks. They visit only every seventeen years, but their song and mess leave quite an impression. As you sweep these critters off your porch or car this summer, you might ask why there are so many.

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Scientists say cicada’s don’t breed a lot just to bug you - it’s a survival strategy.

Chris Dietrich studies insect evolution at the Illinois Natural History Survey.

He says cicada species survive by overwhelming anything that might eat them.

Dietrich: There are never enough predators around when these mass emergences occur to clean up the entire population, there are always going to be plenty of cicadas left over to mate and reproduce.

Dietrich says you see this swarming strategy all over the animal kingdom.

Think, schools of fish or herds of wildebeest in Africa.

Still, researchers aren’t clear exactly why cicadas swarm only once in a while.

I’m Shawn Allee.

Chicago Public Radio.

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