By Emma Joliff
It is cluster fly time again and every autumn the problem seems to get worse.
The flies emerge from the soil and cluster for warmth in farm buildings and houses.
The only people happy to see them arrive are those who are paid to get rid of them.
Cathy McAlister's house is being invaded by thousands of cluster flies each day – resembling more of a plague than a cluster.
“I use vacuum cleaners - one for doing the flies, one for doing afterwards due to the residue that goes up the vacuum cleaner and the constant smell of the flies,” explains Ms McAlister.
Cluster flies are much smaller than a blue bottle, but about the same size as a regular house fly. They first appeared in Auckland in the mid 1980's and they are now widespread in both islands.
Once the flies get in, they are very hard to get out.
“One fly gets in and starts to release a pheromone and that pheromone attracts lots of other flies,” explains researcher Scott Hardwick.
“The hotter it is the more they come in and fly around,” says Ms McAlister. “You have to check your cooking, your cups of coffee.”
The flies lay their eggs on the soil. The larvae then burrow down to feed on earthworms. When the adult fly emerges it seeks a warm, dry place to hibernate in over winter.
This year the worst affected areas are the Wairarapa, Manawatu and Horowhenua.
Last year pest controller Mark Atkinson treated six properties in total for cluster flies. Now he is treating up to four a day.
“I’ve seen woolsheds so bad that they’ve blacked out the windows,” says Mr Atkinson.
Experts say a warm moist summer has been good for earthworms and therefore good for cluster flies.
Pest controllers will treat Cathy McAlister's house with insecticide dust in the roof cavity and spray the walls. But Agresearch says within two weeks the flies are likely to be back.
3 News