BAN LOMTUAN, Thailand -- Preecha Jiabyu used to take tourists on a rowboat to see the banks of the Mae Klong River aglow with thousands of fireflies.

This 2006 photo released by firefly expert Anchana Thancharoen of Kasetsart Univercity in Bangkok, Thailand, shows the rare firefly species Luciola aquatilis, as it perches on a plant. [Agencies]

These days, all he sees are the fluorescent lights of hotels, restaurants and highway overpasses. He says he'd have to row a good two miles (three kilometers) to see trees lit up with the magical creatures of his younger days.

"The firefly populations have dropped 70 percent in the past three years," said Preecha, 58, a former teacher who started providing dozens of row boats to compete with polluting motor boats. "It's sad. They were a symbol of our city."

The fate of the fireflies drew more than 100 entomologists and biologists to Thailand's northern city of Chiang Mai last week for an international symposium on the "Diversity and Conservation of Fireflies."

They then traveled Friday to Ban Lomtuan, an hour outside of Bangkok, to see the synchronous firefly Pteroptyx malaccae, known for its rapid, pulsating flashing that look like Christmas lights.

Yet another much-loved species imperiled by humankind? The evidence is entirely anecdotal, but there are anecdotes galore.

From backyards in Tennessee to riverbanks in Southeast Asia, researchers said they have seen fireflies, also called glowworms or lightning bugs, dwindling in number.

No single factor is blamed, but researchers in the United States and Europe mostly cite urban sprawl and industrial pollution that destroy insect habitat. The spread of artificial lights also could be a culprit, disrupting the intricate mating behavior that depends on a male winning over a female with its flashing backside.

"It is quite clear they are declining," said Stefan Ineichen, a researcher who studies fireflies in Switzerland and runs a Web site to gather information on firefly sightings.

"When you talk to old people about fireflies, it is always the same," he said. "They saw so many when they were young and now they are lucky now if they see one."

Fredric Vencl, a researcher at Stonybrook University in New York, discovered a new species two years ago only to learn its mountain habitat in Panama was threatened by logging.

Lynn Faust spent a decade researching fireflies on her 40-acre (16-hectare) farm in Knoxville, Tenn., but gave up on one species because she stopped seeing them.

"I know of populations that have disappeared on my farm because of development and light pollution," said Faust. "It's these McMansions with their floodlights. One house has 32 lights. Why do you need so many lights?"

But Faust and other experts said they still need scientific data, which has been difficult to come by with so few monitoring programs in place.