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BAN LOMTUAN, Thailand : Thousands of fireflies fill the branches of trees along the Mae Klong River here, flashing on and off in unison - relentless and silent, two times a second, deep into the;night.
Nobody knows;why.
“It's one of the most amazing things you'll ever see,” said Sara Lewis, a professor of biology at Tufts University, close to Boston.
The fireflies, all males, sit on the tips of the leaves and hone their flashes into a single synchronized mating call - and then continue without a pause as if they were driven by an invisible;motor.
In recent years, these pulsating trees have drawn visitors on firefly-watching tours, particularly in Thailand and Malaysia. Evolutionary biologists have studied synchronous flashing for 200 years, she said, and it remains a;mystery.
This retreat is part of a broader problem that is drawing new attention from scientists: Here and there around the world, it seems, firefly populations are;disappearing. But the traffic of motorboats and the riverbank development they have attracted seem to be driving the fireflies;away. “Where are they going? Why? What's happening to;them?”
Like many creatures, from orangutans to salmon, the fireflies appear to be suffering from the worldwide destruction, degradation and fragmentation of their habitats as human development;spreads.
“It's only recently that we are having these questions,” said Christopher Cratsley, a firefly specialist at Fitchburg State College in Massachusetts.
Male fireflies flash to attract females, and, when a female winks back, the two can meet and mate.
Unlike most others, they also face a threat that is as ephemeral as their tiny flashes: light pollution, the same blurring of the skies that has made it difficult, in much of the modern world, to see stars;clearly.
“Anyone with a bright flashlight or a set of headlights that sweeps through will make them get off rhythm for a while, and then they get back,” said Lynn Frierson Faust, a firefly researcher from Knoxville,;Tennessee. Light from buildings or urban development - or even reflected off low-lying clouds on a dark night - can blind or distract;them.
The scientists were here not long ago as part of the second annual symposium of firefly specialists - a small niche in the ecosystem of scientific;specialties.
In controlled experiments with calibrated levels of light, the scientists say they have observed what they call “failure to mate” as the lights get;brighter.
“Where there used to be fireflies there are now big houses with garden lights,” he said.
The symposiums were organized by Raphaël De Cock, a firefly expert at the University of Antwerp in Belgium, who has begun to map their populations in order to track their apparent;decline. Of course, no one was examining for fireflies - or glow worms - so we go with the information that we;have. “But we have only had surveys the last couple of years. A generation ago, they say, the flashing trees were so thick along the riverbank that they served almost as highway beacons for boatsmen in the;night.”
The people who live along the Mae Klong River, an hour south of Bangkok, offer the kind of anecdotal evidence that has caused concern.
Fishermen worked in their nighttime glow, said Pisit Ek Thaiprasert, 40, a firefly conservationist who lives close toby.
“The light from the fireflies helped us see the curves and junctions of those canals at night and helped us paddle through,” said Klao Sakulnum, 68, who has lived here since she was a;child.
Since then, he said, development and firefly tourism have reduced their population along this part of the river by;two-thirds.
Since then, he said, development and firefly tourism have reduced their population along this part of the river by;two-thirds. .
“We're still at the level of trying to figure out how many species we have, what exactly they are, how to tell them apart,” she;said.
The most common estimate is that there are about 2,000 species; new ones continue to be;discovered.
On the other hand, researchers have studied the flash patterns of some species with such precision that they can masquerade as a female and bring a male flying to;them.
“We can actually go out into a natural population of fireflies and we can actually talk to fireflies using a simple, drugstore LED light,” Lewis said. “Really, really;great.”
Fireflies live for only two or three weeks in their adult stage after spending a year or two as grubs. Most adult males spend the evenings drifting through the air flashing sedately until they find their mate - or until they are chased down by a child and put into a glass;jar.