Cicadas, They're Back!

Adult cicada
Photo courtesy of the Indiana Academy of Science

If you live in the Northeast, soon you'll be hearing the drone of periodical cicadas. They've been living underground for 17 years. Now they're back, and they've got one thing on their mind — finding a mate.

What's That Noise?

The male cicadas make the distinctive noise with an organ under their wings called the tymbal, which is sort of like a drum pad. "Basically the calling attracts the cicadas to the treetops," says Michael Raupp, professor of entomology at the University of Maryland, who has a website called Bug of the Week. "It's a way for them to aggregate. They're saying, 'Party up here!'"

It may be music to their ears, but to us, not so much. In fact, the group call is so similar to the sound of machinery that even the cicadas are sometimes fooled. "Leaf blowers, weed whackers, even some riding lawn mowers send out vibrations that trigger the same response, and the males will swarm users of these power tools," says Gene Kritsky of the College of Mount St. Joseph, author of two books about cicadas.

Once the party's gathered — ideally in a tree rather than on a mower — the male has three more types of calls that he uses to woo a potential mate. There are three species of 17-year cicadas that emerge simultaneously, so the first call is to make sure she's the same species. "The first call is like 'Do you come here often?'" Raupp says. "The second is 'That's a lovely dress,' and the third is 'Let's go back to my place.' If she's impressed, she'll respond with a little dance and clicking."

A Magical Life Cycle

We see periodical cicadas more often than every 17 years because there are 12 groups, called broods, and their emergence is staggered. There are also three broods of 13-year cicadas. Seventeen-year and 13-year cicadas will emerge at the same time once every 221 years.

Cicadas that appear every year are found all over the world, and those are the ones you hear later in the summer. But periodical cicadas only occur in eastern North America, and their life cycle is unique in the animal kingdom. It's so amazing that it's even reflected in their Latin name, Magicicada, which was given to them, Kritsky says, because "it tied into the fact that their life cycle is almost magical."

Kritsky has researched this life cycle back to the first written evidence of European settlers' encounters with these insects in the 17th century. Earliest formal scientific descriptions began a long tradition of confusing cicadas with another insect that appears in massive swarms.

Cicada or Locust?

Paul Dudley first saw periodical cicadas in 1699, and when he saw them again in 1716 he wrote up a paper. But, Kritsky says, "he wanted to make sure it was right, so he waited another 17 years." However, when Dudley finally sent his manuscript to the Royal Society in London, it had one big error: He called the insects locusts. When they wrote back to correct him, he was unconvinced. "He said he showed them to a reverend who said that definitely they were the locusts eaten by John the Baptist," Kritsky says.

The society arranged for a real locust to be sent from Cairo to Boston so that Dudley could compare. His mistake was obvious because the two insects don't have a lot in common except for the fact that a whole bunch of them appear at once. That's a strategy called "predator satiation."

"If you've ever been in the midst of a big emergence, you see literally everything eating them: raccoons, birds, dogs, cats. It's like walking outside and the whole place is being inundated with flying Hershey's Kisses," Kritsky says. "That's part of the cicada survival strategy: Everything out there can eat their fill of them and there's still millions left."

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