How to keep flies out of your house as pest population booms due to 'perfect environment'

The hot, wet weather means the fly population is booming.
The hot, wet weather means the fly population is booming. Photo credit: Getty Images

Leonard Powell for RNZ

It's that time of the year again, there's a buzz in the air, and not the good kind.

It's the season of flies, and the wet holiday period means they are popping up by the thousands.

Now that the sun has come out after days of muggy, wet weather, chances are you'll be reaquainting yourself with the unwelcome visitors.

Using fly spray, swats, screen doors and even home-made towel whips were some of the methods that people on the streets of Auckland told RNZ they use to deal with flies.

But why are there so many? Are there more flies than normal?

Cheryl Smith is the director of North Pest, and has run it with her husband since 2015.

Business is booming for the Whangārei-based company, which is currently booked out two to three weeks in advance.

Smith said the weather this summer had been ideal for flies to breed.

"The perfect breeding conditions for flies are heat and moisture. Heat, moisture is what we've got, so flies are thriving."

North Pest treats houses for flies by applying residual insecticide to areas flies are likely to crawl, such as ceilings, walls, door frames and even the eaves on the outside of houses.

They also place fly bait in areas like rubbish and recycling bin lids, and sell commercial-strength fly spray for when instant action is required.

But even with these treatments, Smith said it is not easy to get rid of flies completely, so people should educate themselves how to keep them out of the house.

"Making sure there's lids on compost bins, making sure you pick up any dog droppings and put them in a rubbish bin, and that rubbish bin also has a lid.

"We recommend freezing food scraps until rubbish day so you're not attracting flies in the first place.

"And keeping your lawns down, keeping foliage cut back, so that the air flow can go through. It all just helps to keep fly populations down."

Smith said airflow is key. Flies avoid the wind, so having indoor fans can help to deter them from hanging around.

The classic can of fly spray doesn't always do its job either, according to Smith.

"I think flies can become resistant to fly spray, but I also think the quality of the fly spray perhaps isn't that great over time.

"The fly spray that we have has three different active ingredients, so I think it's better.

"The active ingredient is an important aspect of the quality of fly spray, and of course not many people look for what the active ingredient is, they just look at a dead fly on a can and hope that it'll work."

In more comforting news, as cockroaches make their presence felt this summer, Smith debunked the theory that crushing a cockroach will spread its eggs.

"It's a complete myth because if you squash the cockroach, you're also squashing the eggs, and the eggs can't survive being squashed, as the cockroach can't either."

And be warned - we haven't reached peak fly season yet.

"Generally and historically, the problem is still going to get worse. It's usually in our experience the worst from January to March, and then they continue to linger on right through until June.

"Once the winds stop and people go outside and start cooking the barbecues and what have you, it's really hot and everybody's got their doors and windows open and they're cooking lovely smells, the flies just come out.

"That's their perfect environment."