Facts about periodical cicadas

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Cicadas are a sign of warming spring weather in many parts of the U.S. (Shutterstock)

As the weather warms up from winter to spring, the sight and sounds of cicadas are a mark of the changing seasons.

While annual cicadas are found around the world, periodical cicadas are only found in eastern North America.

Magicicada periodical cicadas have lifecycles of either 13 years or 17 years.

According to Cicadamania.com, "Scientists speculate that one reason why these cicadas emerge in 17 or 13 year cycles is because those are prime numbers. The fact that 13 & 17 are relatively large prime numbers makes it difficult for predators to synchronize with them."

There are 15 different broods (or groups) of periodical cicadas, three groups of 13-year cicadas and 12 groups of 17-year cicadas. Though there are many broods, they almost never emerge in the same year.

"17-year and 13-year broods co-emerge every 221 years." according to Cicadamania.com. "Cicada broods usually don't overlap geographically, and it is very rare when they emerge in the same year."

The broods emerge in the spring once the soil eight inches below the surface reaches 64 degrees Fahrenheit. The adult cicadas emerge to molt and mate. The insect noises commonly associated with cicadas are male mating calls.

After mating, the adults die and the larvae hatch and burrow beneath the soil to begin their 13-year or 17-year lifecycle.
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