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.
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.