The New York Times, June 30, 2013
If you are still waiting for Swarmageddon to break out in your backyard, it is time to stop. The great cicada invasion is winding down for 2013, and it will not be back for another 17 years.
After dwelling in the ground since 1996, the insects began to emerge in May from North Carolina to the Hudson River Valley. In yards, forests and fields up and down the coast, they trilled by the billions, mated, laid their eggs in branches and left exoskeletons on bushes and walkways. Now their song is fading.
But while many people were kept up at night by the roar of this arthropod flash mob, others were left to wonder what all the fuss was about.
“People are disappointed, because the cicadas just aren’t everywhere,” said Chris M. Simon, a biologist at the University of Connecticut.
In New York City, cicadas besieged much of Staten Island, but other boroughs have been quiet. In Philadelphia, the local NBC station declared this spring to be “The Cicada Invasion That Wasn’t.” And while parts of the upper Hudson Valley crunch from the residue of carcasses, most of Westchester County has gone straight from a rainy spring to an incursion of mosquitoes and the emergence of fireflies.
In Guilford, Conn., you can drive around most of the town and not hear any cicadas. But along a stretch of County Road, the red-eyed insects buzz lazily from tree to tree, sometimes devoured in midflight by birds. Even now, there are still fresh, dime-size holes in the ground where new adults are emerging. Meanwhile, the cicadas that came out earlier this year are dying off, their bullet-shaped bodies littering forest trails and roads.
“It makes my 6 a.m. run a little grim,” said Sarah Williams, a County Road resident, as she cupped a live cicada in her palm.
But the cicada season was neither a bust nor another example of media overhype. At least scientists do not think so. In fact, scientists agree that the current brood has had a good year.
Dr. Simon and other cicada experts spent the past few weeks traveling from patch to patch to create the first highly detailed maps of the cicadas’ emergence. In their cars, they have used new GPS dataloggers to record the precise location of each population they encounter. They have built several Web sites for people to submit cicada sightings online. And they are analyzing the DNA of this year’s cicadas to understand how they are related to one another.
This new research promises to give scientists a better understanding of why the cicadas emerge where they do. In future cycles, we may be able to know if their numbers are shrinking, as some researchers fear.
The data that cicada researchers have gathered this spring is vastly richer than what they had in earlier cycles. In the late 1800s, American entomologists created the first good maps of the cicadas’ ranges. Using a Victorian form of crowdsourcing, they sent circulars to all the postmasters in the Eastern United States each year and recorded the responses.
It became clear that the so-called periodical cicadas live in widespread broods containing billions of insects. Each brood consists of scattered populations across the country, which all appear simultaneously on either a 13- or a 17-year cycle. This year’s brood is known as Brood II.
Some people who were disappointed by this year’s Brood II may have gotten it confused with other broods. Brood X, for example, emerged in 2004 in much of the Eastern United States as well — but nowhere did it overlap with Brood II. The next generation of Brood X cicadas will not reappear until 2021.
The early reports of Brood II revealed a range concentrated in the Eastern states, but included pockets of cicadas as far west as Michigan. In 1979, Dr. Simon gathered a fresh batch of data on Brood II by writing an article in Natural History. She asked readers to report cicada sightings to her. She was flooded with responses, mostly from the East Coast, which she combined with the earlier reports to create an updated map.
Scientists have used Dr. Simon’s map to judge this year’s performance.
“Brood II has been exuberant here in Pennsylvania,” said Marten J. Edwards, a biologist at Muhlenberg College in Allentown who has been mapping the insects in the state. “I have been amazed by the extent of the range, which was not documented in the historical record.”
Dr. Edwards has encountered most of that exuberance in thinly populated parts of the state, however. “It’s very understandable that there is a sense of disappointment,” Dr. Edwards said.
This year has also brought some surprises. People in Oklahoma saw Brood II cicadas for the first time — 800 miles west of the next closest emergence this year. Dr. Simon suspects that at some time in the past, some of the cicadas from a different brood in Oklahoma fell out of their regular cycle and emerged in the wrong year. They’ve been part of Brood II ever since.
“That’s what keeps happening all through the United States,” Dr. Simon said. “That’s why you get the jigsaw pattern.”
Another reason for the jigsaw pattern is that cicada populations sometimes disappear. Cold springs may kill off some of the insects. And humans have played a part, too.
By clearing trees for farming, early colonists made it harder for female cicadas to find places to lay their eggs, and for larvae to find tree roots to feed on.
In 1907, the entomologist Charles L. Marlatt was already mourning the cicada’s decline. “To the lover of nature,” he wrote, “there is something regrettable in this slow extermination of an insect which presents, as does the periodical Cicada, so much that is interesting and anomalous in its habits and life history.”
Marlatt did not realize it at the time, but the Eastern forests were about to rebound. As they grew back, it is possible that some cicada broods grew as well. But by the 1970s, development had stopped the recovery. Now the forests are on the decline again, and cicadas may be becoming even more fragmented than before.
Dr. Simon can see the effect on the cicadas when she goes back to historical sites. In Port Jefferson Station on Long Island, for example, Dr. Simon went to a forest where she had collected cicadas before, only to find a Walmart in its place.
“A big asphalt parking lot instead of a forest would definitely put a damper on the population,” she said.
Unfortunately, Dr. Simon and her colleagues do not have enough data to tell the full story of Brood II’s expansions and fragmentations over the centuries. “It’s too bad that back in the 1700s we didn’t have GPS dataloggers,” she said. “It would be nice to know what they looked like before the colonists cleared the trees. We’re starting now too late.”
Copyright 2013 The New York Times Company. Reprinted with permission.