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Australia’s venomous redback spiders are on the march in Japan, where they are believed to have arrived years ago as stowaways on cargo ships, a wildlife expert warned Wednesday. The spiders, named after their fiery markings, have infested the Osaka region and are drawing closer to Tokyo, said Japan Wildlife Research Centre official Toshio Kishimoto.

A dozen people have reportedly been bitten in Osaka Prefecture alone, media reports say, including a six-year-old boy who was treated with antivenom in June, the first time the medication had been used in the country.

“Their poison is strong and they are particularly dangerous to people in weak physical condition, like children and the elderly,” Kishimoto said.

“Redbacks are becoming a common species in Japan. They are very numerous, especially in the western region, and are now often sighted in residential areas. Once the spiders spread, it’s hard to eliminate them.”

Redback bites, which inject a potent neurotoxin, have caused numerous deaths in Australia, although an antivenom stocked in hospitals has prevented fatalities more recently.

Redbacks were first spotted in Japan in 1995, around Osaka, a major port where, experts believe, they may have arrived in a container of Australian woodchips used to make paper in Japan.

Several years ago, a major redback infestation was found in the street drainage system of the city, and the arachnids have now spread to prefectures covering roughly a third of the country.

Kishimoto said Japanese people must become more aware of the dangers of redbacks, a species long feared in Australia, where the creatures are known to lurk in garden sheds, in shoes left outdoors, and under toilet seats.

“People need to be warned on how to treat them, and to be careful when they’re out cleaning ditches, and to wear thick cotton gloves for example,” said Kishimoto.