Warmer days and warmer nights are making it harder for sprays to work on some flies and people may just have to grin and bear the critters, says a Rotorua pest controller.
"If the house is very hot and sticky and you are sleeping with just a sheet the flies won't be as affected [by fly spray] as if it was cooler. You'd expect to find them on the floor dead when you get up but instead they are making breakfast for you," says Chris Brunel, manager of Rotorua's Bay Pest Services.
"Those tiny house flies that don't really head for the window but sit on the end of your nose and on tea towels, they are very difficult to get rid of."
Mr Brunel said people getting their homes sprayed needed to be realistic and realise it won't completely get rid of the flies.
With temperatures not going down too low at night, some of the pesticides had limited value.
He said some fly sprays were only effective in "certain temperature zones". He was not able to say what temperatures as it depended on what sprays were used.
Mr Brunel said they were getting about two or three calls a day about flies or spiders including white tail spiders. However, he said the number of calls was on a par with the same period last year.
Rotorua has had problems with white tail spiders for many years and Mr Brunel said they had not seen an unusual spike like other centres, including Gisborne where the number of white tails had been worse this summer.
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Rotorua Pest Control owner Neil Olive said this summer was busier than last summer but that was because "there was no summer last year".
"Anything over 22C or 23C they [flies] are starting to come out. It's a lot hotter than last summer so out come the insect world."
A Fairy Springs resident, who did not want to be named, said this was the worst summer for flies in the 10 years she had lived at the property and she was going through a can of fly spray every few days.
She went to three local retailers to buy more fly spray but they had all sold out.
"Before I got some fly spray I literally walked through a swarm of flies."
A Pukehangi resident said she had fly spray on a timer as well as a can of fly spray but they didn't seem to be killing all the flies. She said there were a lot more flies around than in previous years.
"One night we looked up at the ceiling in part of our kitchen and there were about 15 little flies. I've never seen anything like that," she said.