An unusually wet summer in parts of the country has created the perfect environment for a plague of cluster flies.
Canterbury is one of the worst-hit areas of the cluster fly plague, with black clouds of the insects invading homes and no easy way of getting rid of them.
As the name suggests, cluster flies aren't often seen alone - and when you're dealing with an infestation, they can be overwhelming.
"They're disgusting and they leave a mess; they poo everywhere inside your curtain linings and all along your walls inside door frames and the window frames," Hayland farm's Clare Hammond told Newshub.
This Autumn they've been particularly bad.
Guaranteed Pest Control's Daniel Highman said he hasn't had to get rid of any other pests for ages.
"I don't think I've done a job other than cluster flies for the past five weeks. It's pretty annoying when they go up your sleeves and your whole suit is vibrating."
The thing that sets them apart from your regular house fly other than the obvious is their slow, dozy movement.
Parasitologist Allen Heath said the cluster flies were first found in New Zealand, in the mid-1980s.
"They were first picked up in New Zealand in 1984, so they probably came in a shipping container because of this habit they have of trying to find somewhere dry and warm to hibernate over the winter months."
This is why they're being seen in houses - and with climate change causing wetter, warmer weather, we'll likely see more.
"They like moisture and they like heat and they like worms, the females go and lay their eggs in the grass. The maggots hatch and they crawl down the soil space to the worm," Heath told Newshub.
Highman says they're not considered a filth fly, meaning they don't breed in meat.
Canterbury and Wairarapa have been hit hard this year - they're common in rural areas and this year also in town.
Highman says they might clog up your vacuum if you try to get rid of them that way.
"They've got an oily residue which is a pheromone that they let off, which is quite sticky."
If you imagine hoovering up hundreds of thousands of flies a day, your vacuum cleaner may not last very long.
Highman believes the best approach is preventative pest control and says it's a smart idea to plug up any holes or cracks to stop them from crawling in.
