A protected weevil sent to Mana Island near Wellington is thriving but at the peril of its neighbours.
One-hundred-fifty of the insects were introduced the island, off the coast north of Wellington, between 2004 and 2006, and now they are in their thousands.
DoC ranger Nick Fisentzidis and his family are the only human inhabitants on the island.
He drove RNZ to the south-west end of the Island, where the weevils were first introduced.
It's not long until flax is spotted that has fallen prey to the weevil, with larvae feeding off the roots and adults eating the leaves. The flax was brown and lifeless.
It's not just weevils that needed the flax to survive, but the rare goldstripe lizard and other native fauna.
"Goldstripes feed and live in the flax community, when this stuff is flowering there are oodles of tui and bellbirds feeding on them, so it's super important for the wider habitat of the island to work out how to slow the onslaught."
But work was underway to restore balance to Mana Island.
Te Papa curator Colin Miskelly said they thought the weevil would be a good fit for the Island as the numbers had depleted on the mainland since the introduction of rodents.
"They're big and flightless, so they get eaten by rats and mice, so they're now mainly confined to a few small islands and mountaintops."
But now, the weevil were in their tens of thousands and could easily be seen when they came out at night.
"It took three of us 10 minutes to gather 80 of these insects," Miskelly said.
He had been monitoring the situation on Mana and has helped whittle down why the insects were doing so well.
"Flaxes in the damp sites survive better. One explanation might be the larvae don't like living in muddy conditions, but another possibility is in those damp sites, even if the roots are damaged the plants are still able to get enough moisture."
He expected projects to get underway from early next year, to slow down the growth of the island's weevil population.
