The Year of the Cicada: What the Buzz Was All About
Every 17 years or so the big bugs are back, but briefly
BOSTON — Leave it to a bunch of teenagers to disrupt a quiet afternoon. This summer, hordes of 17-year-old cicadas have been out in force, buzzing to their hearts' content.
Called the world's noisiest insect, the cicada has intrigued and annoyed humans for millennia. Musicians in ancient Greece tuned its instruments to their pitch. Japanese poets wrote haiku to tout the bugs' persistence and courage, and some gourmets crave their "earthy, shrimp-like flavor."
Earlier this summer, Americans from Connecticut to the Carolinas had a rare opportunity to study the latest hatch of 17-year-old cicadas. But this group (or Brood 11 as it is referred to) of 1.5-inch-long insects was only one of dozens that emerged on different 17-year and 13-year cycles across the country to sing, spawn, and die.
As Brood II departed, entomologist Charles Remington had a chance to look at his notes. Asked what he learned from this fleeting brood, he all but gushed.
"We know a lot about the adults, but we don't know much about hatchlings," says the retired Yale University professor, who helped set up the world's first cicada preserve north of New Haven, Conn.
Weeks after their parents had become bird fodder, the ant-sized hatchlings started squirming down to the soil below. Once underground, they feed on the watery nutrients of tree roots (not the sap, which comes down from the leaves) and gradually, over the years, expand into thumb-sized larvae.
Then on some warm evening in June 2013, when the temperature is just right, the brood of cicadas will emerge to continue the cycle. "Right now, the hatchlings are burrowing down as far as four feet to find any viable tree root," says the bug-loving professor. "Anything except pine. The heavy resin of the pine is not great for their delicate little mouths."
"The trigger is definitely ground temperature," says Chris Simon, an evolutionary biologist at the University of Connecticut at Storrs. "If you used Staten Island [New York] as a marker over the past 100 years, the time of emergence for Brood II has remained steady. It may drag out over two to three weeks, but the peak is always on a certain night."
Over time, cicadas have developed several strategies for survival. For instance, scientists noticed this year that cicadas waited to emerge at the beginning of darkness.
Under cover of darkness, the soft, white adolescents can avoid daytime predators while they develop the hard, black exoskeletons of adulthood. "In hindsight, the behavior makes perfect sense," Dr. Remington says, "but we had never noticed it before."
Some behaviors are better understood than others. For instance, male cicadas tend to emerge a week before females, Dr. Simon says. This allows the males to establish their territory and practice their come-hither buzzing sirens. But this also signals starlings and other birds that soup's on.
"Males are expendable," Simon says with a sigh. "One male can fertilize lots of females' eggs. Apparently, predators do get tired of eating one thing after a while, so the females have a better chance of survival."
But while this Darwinian struggle takes its toll, plenty of male cicadas survive to sing out strong.
Tens of thousands of surviving males congregate in the branches of each "chorus tree," and tens of thousands of silent females soon join them. The cicada's drone can be heard a quarter of a mile away, and a cicada rarely sings alone.
Yet despite all this study, one central mystery remains: How do cicadas keep track of time? "There's got to be a molecular clock that is counting off the years," says Simon. (There are also 13-year cicadas in the South and more common Dog-Day cicadas that have an even shorter life span.)
"If you dig up nymphs after nine years, you'll find them growing at different rates," she says, "but they all come out within a week or two of each other."
Cicadas are often mistaken for the Biblical swarms of locusts, which nibble whole fields of grain down to stubble. Cicadas are much more benign, but they do have an effect, particularly in areas where several broods overlap. As many as 40,000 cicadas may emerge from under a single tree.
Fruit orchard owners complain of lower yields in the four years before the cicadas emerge. "But just afterward, they have a record harvest," says Simon. Because cicadas feed off the diluted nutrients from the roots, they grow slowly and "reach amazing population densities without killing the trees."
At the Connecticut cicada preserve, researchers have bagged hundreds of cicadas and put them in the deep freeze for later study. In time, the bugs will be thawed and served up in a kind of taste test for birds, mammals, and even a few willing humans.
"Cicadas may be the tastiest insect in the world," says Remington, who has written articles and a book on edible insects.
I'll take his word for it.