It's raining lizards on Mana Island.

Seconds after Andrew Blanshard​ warns the historic woolshed is full of the reptiles, one drops from the ceiling, hits the floor and weaves away.

In the rafters above, hundreds of tiny heads can be seen peering down on the human intruders – the only pests on the table-shaped chunk of land three kilometres off Porirua.

VIRGINIA FALLON/STUFF An island to one's self: Tyke sails away from Mana Island.

"The lizards are everywhere, the place is bloody crawling with them," Blanshard said.

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Blanshard​ and his dog, Tyke, work for the Department of Conservation, and they're are on Mana to make sure the lizards can keep crawling.

VIRGINIA FALLON/STUFF Lizard life on Mana Island is booming after eradication on pests.

Tyke is a predator dog, whose job is to scout for the rodents that could destroy the island's native wildlife.

Discarded gecko skins carpeting the ground are testament to the duo's success.

"A good day for Tyke is a bad day for me. If he finds something it's the start of a whole lot of work for a whole lot of people."

VIRGINIA FALLON/STUFF Lizard skins litter Mana Island, proof of the massive reptile population.

It's a lot of responsibility for the little border terrier, trained to sniff out the undesirables, but there's no doubt he loves his job.

He never really stops looking for vermin, it's part of his breeding but he also knows when it's business time, the ranger said.

The mice that plagued the island were eradicated in the early 1990s, but the department remains vigilant.

VIRGINIA FALLON Mates: Andrew Blanshard and his dog Tyke have been working on Mana Island, off Porirua, ensuring it remains pest free.

They have a canine arsenal, the dog squad, that checks the islands. The dogs are each specifically trained, some hunt cats, some rats, and others possums.

Sporting a muzzle to prevent any over-excited accidents, Tyke scours the island sniffing for the tell-tale scent of intruders among the native trees, 500,000 of which had been planted by volunteers.

A find is indicated by a change in behaviour allowing Blanshard​ to set traps and plot the location on GPS for further exploration.

VIRGINIA FALLON/STUFF The view from the historic woolshed on Mana Island towards Porirua

The checks are routine and, this time, Mana was given the all-clear, resulting in a "very bored" dog.

It's tough for Tyke to keep searching for something he never finds, Blanshard​ said.

"We have a freezer full of rats, which my wife really loves, and I have friends who live-capture so we can keep his training up."

VIRGINIA FALLON/STUFF Tyke the predator dog. The six-year-old border terrier is trained to hunt vermin.

It's not just the lizards that live predator-free on the island, the noise of native birds is ever present and a group of shags reluctantly shuffle aside to let the pair pass.

"There's a lot of birds just sitting around on the ground here because they're safe."

It was a flying trip to Mana, three days later the pair climb aboard the DoC boat and head to Matiu/Somes Island in Wellington Harbour.

Blanshard​ hopes for another uneventful trip. Tyke never gives up the hope for rodents.