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[Note] This article about the Science in the News Exhibit case and cicadas in general was written for an in-house Smithsonian Institution, Staff Publication.

They're back:
17-year cicadas


By Michael Lipske
Special to The Torch

See caption.
 
Tom Thill, Sarah Grusin, Nathan Erwin, and
Gary Hevel. Photo by Harold Dorwin.
(Click here for larger image)

There will be love songs in the air inside the Natural History Museum this spring and summer-ballads and standards to make the heart flutter, if you are a cicada.

"We have a whole CD of recorded cicada sounds," museum Exhibit Writer Sarah Grusin says happily. With 51 tracks of pure cicada gold to choose from, Grusin plans to have insect-courting music playing as a backdrop to a new display she is preparing on the reappearance of the 17-year cicada in the Washington, D.C., area.

"We're going to call it 'Treetop Opera,'" Grusin says of the display, located on the museum's first floor. The small exhibit is a nod to the year's big insect news.

Starting in mid-May, billions of cicadas will begin crawling out of the ground across the Washington, D.C., area. During the following weeks, the insects will molt, climb into trees and, in the case of male cicadas, blast out the loud droning that is the cicada seduction song.

But it's not just any cicadas the museum is celebrating. This year marks the return of Brood X. Spawned in 1987, the nymphs of Brood X have spent 17 years underground, feeding on fluids from the roots of trees.

Years ago, a U.S. Department of Agriculture scientist started the practice of using Roman numerals to identify different broods of the insects called periodical cicadas; each brood consists of a cohort of cicadas, all of the same age and thus isolated from other broods by time. Twenty different cicada broods are known to exist in eastern North America. Each emerges like clockwork in different years.

Scientists theorize that the long period between emergences helps confuse unsuspecting predators, most of whom do not live as long as the cicada and, therefore, have never seen one. Whatever the reason, "It's worked for millions of years," says Nathan Erwin, director of the museum's Insect Zoo. "For them, it's a great way of making a living. If they can mate and pass their genes on, then 'bingo!'"

The cicada exhibit was Erwin's idea. (Sarah Grusin says she was on a coffeebreak when "Nate came along and said, 'The cicadas are coming.'") The intrepid entomologist has not only eaten cicadas-"they have a bit of a nutty taste"-but also spent several nights 17 years ago photographing and marveling at the emerging representatives of Brood X.

"It's an amazing natural phenomenon," Erwin says. "Just the sheer numbers of them. There have been estimates of a million per hectare [about 2.5 acres]." And those numbers result in "this incredible sound," as courting male cicadas commence their chorus.

In the display case, an enlarged model of a cicada will show the drum-shaped organs, called tymbals, males use to create their mating calls, which vary from species to species. Three species of cicadas belong to Brood X.

Cicada specimens from MNH's collection also will be on display, along with information on how the insects while away their 17 years below ground and their few weeks of treetop courting and reproduction.

The exhibit will include a photo and short biography of the late Richard Froeschner, a former MNH entomologist, whose frequent lectures on periodical cicadas earned him the nickname Dr. Cicada.

Lately, the job of responding to the public's questions and worries about periodical cicada invasions has fallen to Gary Hevel, public information officer with the museum's Department of Entomology. Hevel tells people that, despite the mind-boggling numbers that will make up Brood X and the correspondingly loud racket from the males, cicadas are harmless. "They don't bite or sting," he says.

Female cicadas scratch slices into thin tree branches while laying their hundreds of eggs; as a result, trees start dropping twigs by the end of cicada season. The young cicadas hatch from their eggs and fall to the ground either in the twig or take a "swan dive" to the ground, where they burrow, Hevel says. The tree "pruning" by cicadas won't hurt large trees, Hevel adds, but "people may want to put cheesecloth over saplings to keep cicadas away."

In addition to gardeners, Hevel has been hearing from people worried about Brood X's impact on May and June weddings. If you shudder at the thought of airborne cicadas crashing into guests or splashing into punchbowls, he suggests celebrating the wedding indoors. On the other hand, Hevel says, some brides and grooms probably will accept Brood X members as uninvited but memorable guests. Although even Hevel, a confirmed cicada admirer, admits that the background din from singing males "might be a problem for hearing the wedding couple say 'I do.'"


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