They trigger fires, prey on the elderly and thrive in the cement jungles of Japanese cities. But Japan's latest urban predators aren't delinquents or gang members -- they're rats.

Complaints about the rodents have soared over the last decade, and cities have devoted officials to the task of wiping them out. Recently, Tokyo hosted its first anti-rat symposium.

The vermin nibble electrical wires that spark fires, nest in the homes of Japanese cities' growing population of elderly and infirm and wake residents when they noisily scurry around crawl spaces and through plumbing.

They're also making more regular appearances in Japan's urban commercial districts. Hideaki Okuzawa, who fills soda vending machines in Tokyo, said he and his co-workers often encounter the creatures.

"A colleague found a nest with a baby rat when he opened a vending machine," Okuzawa said, grimacing in disgust. "I wouldn't be able to stand it."

Rats are hardly a new phenomenon in the world's big metropolitan areas. But Japanese officials think the surge in rat sightings in their cities is being fueled by the spread of roof rats -- known scientifically as "rattus rattus."

Roof rats are agile building climbers accustomed to living in urban environments near humans. Officials say they are more resistant to pesticides than the Norway rats that have long trolled Japanese gutters and sewer pipes.

"Roof rats are well adapted to living inside buildings," said Fumiko Matsuda, an official handling rat problems for the Tokyo Metropolitan Government. "They're also escaping from old buildings that are being torn down and moving into surrounding residences."

Japanese officials have no estimates on the total rat population. But complaints about rats in Tokyo have increased from 10,241 in 1995 to nearly 20,000 in 2001, though the number dropped to about 16,000 last year. In Osaka, city hall received about 9,200 complaints last year, up 28 percent from 1996.

It's not only an aesthetic problem. The Tokyo Fire Department said there have been 115 fires linked to rats since 1995, causing 22 injuries and $3.2 million in damage. Many were caused by chewed wiring.

Rat watchers say Japan's rapidly aging society provides a haven for rodents. The theory is that the rats find shelter and food in the cluttered, unkempt homes of older people who have trouble keeping up with housework.

At the Tokyo rat symposium in July, officials described troubling scenes of infestation: a rat that stole candy from the plate of an 83-year-old woman with Parkinson's disease; a 78-year-old widow who discovered a rat in her bed.

Matsuda said officials may have only scratched the surface of the rat problem, speculating that infestation in supermarkets, department stores and railways has yet to be fully revealed.

Moves are afoot to stamp out the critters. Tokyo is scheduled to come up with anti-rat guidelines by April.

In the meantime, some folks are taking matters into their own hands.

The Tokyu Hands department store noticed a spike in requests for rat-killing products a few years ago, and now it has a full line of devices, from traditional mousetraps to a high-tech contraption that uses a rat-scaring sensor. It sells for $480.

But the best way to keep rats out may be not devices, but discipline.

"If you leave the trash out long, they'll come," warned store clerk Kazuhiro Yoshiki. "The best solution is to keep your place clean."