Cluster flies drive woman to despair

Frustrated rural dweller Sandra Hunt seals off yet more windows in her Maungati house to prevent the entry of thousands of cluster flies. "Something's got to be done about it. I'm the one who has to bear the cost of spraying and the pest-control people say they cannot guarantee the flies will stay away," Mrs Hunt said.

Her breakfast takes second place to a knot in her stomach as she anxiously peers around doorways in her Craigmore Valley Rd, Maungati, home.

Unwanted lodgers have taken over Mrs Hunt's rented country brick home and the vacuum cleaner is her only form of defence against cluster flies. "Three times a day I have to vacuum the entire house out and they are there again the next day, in their thousands."

She blames irrigation systems in her district, which she said were providing a breeding ground for the pesky, fat, hairy critters.

"Something has got to be done about it," she said.

"I'm the one who has to bear the cost of spraying and the pest-control people say they cannot guarantee the flies will stay away.

"I am stunned that this is happening in this district."

She did not open her windows last summer and probably will not again this summer.

Crevices, architraves and skirting boards in her home are sealed with sticky tape.

"I love the country and the smells and views, but I can't open my windows.

"I am revolted by the flies and I've been told there is nothing I can do," Mrs Hunt said.

"I can't be bothered with this.

"I mean they can land a man on the moon, how come we can't hurt a fly?"Cluster flies, so named because of their ability to communicate with each other using aggregate pheromones to summon themselves into "clusters" - sometimes numbering more than 10,000, are a growing phenomenon in New Zealand, scientists say.

Lincoln-based AgResearch entomologist Scott Hardwick said this was the insect world's most sophisticated messaging system known.

He said the greasy flies had invaded parts of the South Island including South Canterbury and Otago in their millions and had also moved to the North Island in plague-like proportions this autumn.

They could be seen lifting off a paddock like a swarm of locusts.

Cluster flies had been in New Zealand since at least the 1980s when they were first spotted in Auckland, he said.

The name cluster fly or loft-fly, which comes from the Northern Hemisphere, refers to Pollenia rudis Fabricius, and P. pseudorudis that are parasitic on four species of earthworms.

"The adult flies into the pasture and lays groups of eggs on the soil surface. The little maggots hatch and they actually feed on earthworms," Mr Hardwick said.

"The little beasts develop in the earthworm carcass and then they pupate and hatch. Come autumn they have this behaviour where they fly into machinery sheds and houses.

"Interestingly, there can be thousands in one house and none in houses on either side. This is because their aggregation pheromone signalling system sends messages to other flies that they have found a cosy spot to spend cold nights," he said.

"That's why you get these huge clusters of them."

Frustrated home owners have found the flies difficult to deal with.

The weapon of choice has been the humble vacuum cleaner.

But Mr Hardwick said effective control began by breaking the reproductive cycle.

"And that's about either removing the worms or removing the adult flies.

"You can trap the adults with horse dung, meat, fruit and banana and dispose of them to stop them breeding in the vicinity of the house," he said.

"Some people have sprayed the outside of a house with insecticide, but there are some specific environmental issues in doing that," Mr Hardwick said.

Environment Canterbury offers little help to those dealing with cluster flies.

Biosecurity manager Graham Sullivan told Courier Country that the flies were "not a matter for this organisation".

"The Resource Management Act doesn't deal with the problem nor does the Biosecurity Act," he said.

"We do have a pest management strategy, but for pests to be described as pests in that document there is quite a set of criteria that has to be met and one is that the cost benefit to an individual or region is not exceeded by the cost of regional intervention.

"Flies are a problem that a few people in an area may be dealing with, but it's a bit like rats and mice and things like that, they need to be dealt with by a pest-control company," Mr Sullivan said.

"It's a bit like people having a problem with, say, Darwin's ants in Christchurch, or cockroaches in Auckland. The responsibility rests with the land occupier."

If you have had a cluster fly problemand have found a way to deal with them,call Graeme Stilwell on 0274 322-590 or email graeme.stilwell@xtra.co.nz