Lizards threaten unique wildlife on Japan's remote Ogasawara islands
Environmentalists are losing battle to prevent creatures from spreading to other islands
On spindly legs and just 15cm from nose to tail, the green anole lizard does not appear to pose much of a threat. But to the indigenous insects of Chichijima island, 1,000 kilometres south of Tokyo, they are rapacious, fast-breeding invaders that have driven several species to the brink of extinction.
Some of those species are not found anywhere else in the world and there is inevitably a knock-on effect among other creatures in the local ecosystem.
Most worryingly, the lizards appear to have found a way to traverse the channels that separate Chichijima from the rest of the Ogasawara archipelago, which was recognised as a Unesco Natural World Heritage site in 2011.
"We believe the lizards were first brought to the island as pets by the US military when they had units stationed there or aboard transport vessels from Guam in the 1960s," said Yasunari Hattori, of the Environment Ministry's Alien Species Management Office.
The ministry has essentially given up efforts to eliminate the lizards from Chichijima, the largest island in the chain, and has instead implemented a strategy of stopping the creatures spreading.
In March this year, however, the first lizards were found on Anijima Island, which is 500 metres away.
"We are not sure how they managed to do it, but this is a serious problem as Anijima and the other islands are unique ecosystems with insects that are only found here," Hattori told the Sunday Morning Post.
One theory is that tourists visiting Anijima may have inadvertently carried lizards to the island in their backpacks. Equally, the creatures may have stowed away in researchers' equipment bags or the small boats that ferry visitors to the uninhabited island. Some may even have been able to make the crossing on floating logs or rubbish, he said.
The ministry placed 36,000 traps in the southern part of Anijima and caught more than 5,200 lizards by the end of November. A fence is also being erected in an effort to halt their occupation of the island.
Experts say the eradication efforts may be paying off, as numbers on Anijima appear to be declining - although the breeding season is due to start soon.