The little suckers are riding into towns and villages, hitching lifts on deer and boar whose numbers have grown due to re-forestation and dwindling rural populations.

Once there, the leeches, which measure in at about 1.5 cms before a meal, take to feasting on warm human flesh.

"Yamabiru will climb into people's socks and stay for about an hour, growing five to 10 times in size. Unlike with water leeches, people don't immediately realise they've been bitten. Only later when they see their bloodsoaked feet, do they realise what has happened," said Shigekazu Tani, the institute's director.

"The real problem is that the bleeding won't stop and the affected area swells up and really itches," he added.

The best way to deal with the tiny vampires?

"We can cut down trees and mow long grass to dissuade wild animals from coming too close, and create sunny habitats that are inhospitable to leeches. We can also spread pesticides that kill the leeches," Tani said.