Pest controllers are reporting a boom in the rat population as cold weather pushes the pests to shelter inside.
The rise in numbers is attributed to the warm autumn and last year's economic climate, with one Auckland company seeing a 100 per cent increase in rat control calls.
Abolish Pest
Control owner Jason Stobart said his company received twice as many calls last month as it did in May last year.
"The 100 per cent increase is due to people spending less on pest control [during the recession], which allowed rat numbers to drastically grow.
"The problem didn't just remain, but the problem bred as well, and got much worse than it would have been."
Mr Stobart said the warm autumn also had an effect.
Abolish Pest Control has also been needing more bait.
"This year if I go to a house and put down bait they are eating more of it. So they are clearing more bait per individual place as well as there being more jobs in general."
Further south, Wellington Pest Management has recorded a 30 per cent increase in the last quarter - March, April and May - compared with last year. Managing director Darren Labrum said the average yearly increase was 10 per cent.
"We had a late summer this year and it was a quite mild autumn, so they got an extra breeding cycle. They can breed every three months if the conditions are right."
Once their population grew in the wild and the cold of winter hit, rats ran indoors to the warmth of houses and commercial premises, Mr Labrumsaid.
"Rats and mice live hand-in-hand because we are providing them with the essentials of life. We are providing them with shelter, with food, with warmth.
"Out of the bush you are going to have very much boom and bust. It's going to be weather dependent. Whereas in a human environment we're providing them with warmth year round.
"Therefore as our population grows, the rat population grows."
Mr Labrum said the roof was the rat's favourite place, because it was warm and there were no predators.
To prevent numbers creeping up, he suggested stopping the rodents by blocking holes or putting out bait every year, killing them before they became re-established.
- NZPA
