Science: Wedding Whirs

1979 is a cicada year

Already, from the Carolinas to New York, little holes are appearing in lawns and backyards, hillsides and woodlands. Any evening now, out will pop millions of dark little bugs. They will scamper up almost any upright object—trees, poles, buildings—and soon strike up a joyous racket, marking nuptial rites after being buried alive for 17 years.

They are periodical cicadas (pronounced sih-Kay-duhs), the world's longest-lived insects. Despite a locust-like appearance, they neither bite nor sting nor devastate vegetation. Entomologists currently count 19 separate "broods," which appear at various times in different parts of the country, some once every 13 years. But all follow roughly the same miraculous life cycle. Growing through five skin-shedding molts and sucking nourishing juices from roots, they emerge with uncanny precision, triggered by some still mysterious internal clock.

In the open, they shed their dry, yellowish skins for the last time. Soon the males strike up their cacophony of ticking, buzzing and shrill whirring sounds. It is all music to the females, who slit open tree bark after they have been impregnated and store their fertilized eggs there. A few weeks later, both parents die. But cicada life goes on as the eggs hatch. The newborn nymphs drop to the ground, burrow, and the age-old cycle starts anew.

Baffled scientists are still unsure why the cicadas behave as they do, but suspect that it may all be a defense against predators like birds. As Entomologist Chris Simon of the State University of New York at Stony Brook writes in Natural History, when the cicadas finally emerge, it is in the shadows of dusk. They also gain protection from their monstrous numbers—as many as 1.5 million per acre. Finally, since they appear only once every 13 or 17 years, nature may have endowed them with an unlikely mathematical defense. These are prime numbers, divisible only by themselves, and so parasites would have to live at least as long—a half or a quarter would be improbable—to partake in a 17-year feast.