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‘Utterly foul’ flies invade homes

Piles of dead cluster flies can stack up to five or seven centimetres deep. PHOTOS/SUPPLIED

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Plagues of cluster flies are invading Wairarapa homes, clogging vacuum cleaners and piling up on windowsills and floors.

Tinui resident Caryl Forrest, whose home had suffered an invasion of the flies, said the insects were a daily problem.

“Cluster flies are relatively common in rural Wairarapa as they need to lay eggs on grass, and we have plenty of that.

“At their peak, I was having to spray the house with insecticide several times a day and vacuum up to three times a day.

“They tend to congregate on windows and wriggle inside window frames, but you will find them in other places, such as curtains and walls, particularly on outside walls. And they love getting up in the ceiling.”

Forrest said the flies were difficult to get rid of, and dead flies had to be removed carefully.

“Cluster flies prefer rooms that don’t get too much use, so they are a big problem in rural churches which are not used that often, where they can accumulate on the floor in large drifts.

“Cluster flies are full of fat, which means they clog up vacuum cleaners and have to be carefully removed from carpet in case they get squashed.”

Rural Masterton resident Paula Petrie described the flies as “utterly foul”.

“We are in the middle of renovations at the moment, and we are seeing heaps of them falling out as we remove walls,” she said.

“They are utterly foul. They smell, and they clog up the vacuum cleaner. The poor builders went into the roof to do some bits and had to pull the pin as there were so many. They had head torches on, which meant they got swarmed by them.

“We put off four cluster fly bombs up in the roof, which helped, and now they are able to get back to work there.

“The only problem is if you don’t clean the dead ones up, then the pheromone they let off attracts more. And it encourages rats and mice as they eat them.”

Paul Chapman, director of Masterton-based pest control company Pestproof, said the problem was far worse this year than previously.

“This year seems to be much worse than any other year.

“We were getting no calls last year, and this year we are getting four or five calls a day.”

Chapman said the problem could be pinned on Wairarapa’s wet weather over the summer months.

“I don’t know if it’s climate change. We do get bad years; it could be to do with the amount of rain.”

He said that although he dealt with many calls, a call-out was only needed when a population was getting very bad.

“The use of insecticide is a last resort. There are other ways of dealing with them, but we use insecticide when they get really bad.”


Professor of biology at Victoria University of Wellington Phil Lester said that the flies liked the warm and wet seasons. With these seasons extending, the problem could worsen.

Flies laid eggs by earthworm burrows, and the larvae ate the worms. Although it was believed Wairarapa had a healthy earthworm population, extended seasons and more flies could mean problems down the road.

Earthworms played an essential role in breaking down organic matter and fertilising soil, and loosened and mixed the soil as they moved through it.

“It’s too soon to say as Wairarapa has a lot of earthworms, and unless data comes out that says otherwise, I don’t think it’s a problem yet,” Lester said.

He said the flies found holes in the house, and once inside, they hibernated in groups and released an oily pheromone that attracted other flies and stuck around even after a fly had died.

“It’s really important for homeowners who vacuum up and spray to get rid of those pheromones too.

“They will need to do some washing, unfortunately.”

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