When Michael Melville-Barton crawled under his Otumoetai house to fix faulty cables, he was shocked by what he found - a wasp nest big enough to contain "tens of thousands" of the pests.
He snapped a photograph of the nest clinging to the floorboards under his lounge and quickly backtracked.
Experts said it was a German wasp nest which could have contained millions of the insects and was the biggest they had seen.
"When I saw the picture it gave me a bit of a fright," his wife Gemma Melville-Barton said.
"I didn't know actually what it was - but I knew it wasn't good. I saw some dead wasps on the floor below the nest," Michael said.
Fortunately, the nest, which was the size of about six rugby balls, was inactive but he and Gemma were not prepared to take the risk given they had two children, aged 1 and 3.
"There were a few dead wasps around the place, but then a friend of ours saw a couple of live wasps when he was here," Gemma said.
"With young children, you just don't want to take any chances with this sort of thing."
The couple relocated from Auckland to Tauranga with their two children and had been in the house for a month when the nest was discovered.
"There was nothing that led us to believe there was anything like this under the house," Gemma said.
PestCo service technician Mike Wills said the nest had once contained German wasps and in his 20 years dealing with pests he had never seen such a large wasp nest in a building.
"When active this nest would have contained tens of thousands of wasps," Wills said.
German wasps had a potent sting and could attack in large numbers if disturbed or threatened, he said.
"Anyone who was under the house would have potentially been in serious danger had this not been a dormant nest. It doesn't really bear thinking about.
"It was a confined space and there would be nowhere to escape in a hurry."
CrestClean spokesman James Smith said a wasp nest the size of one rugby ball was considered big and this one could have been there for a "couple of years".
"They're quite aggressive; they can be potentially really nasty."
New Zealand has some of the world's highest densities of German and common wasps.
They have no natural predators here: Our winters are mild, and there is plenty of food for them.
The venom from a wasp sting contains several toxins that can cause a hypersensitive or allergic reaction in some people.
German wasp nests are grey. The world's largest recorded wasp nest was discovered at Waimauku (near Auckland). It was 3.75m tall and 1.7m wide.
Source: Department of