Fat rats are brazenly overrunning suburbs across Auckland, and it could become an ongoing problem due to climate change, the association representing pest controllers says.

Auckland's "very hot summer" had driven the rats frisky and "exacerbated their breeding cycle", with pest controllers noticing increased numbers as early as February.

"There has been a huge increase in rats this year," Peter Barry from the Pest Management Association said.

"It is possible that if we have increased summer temperatures in the years to come that this might become an ongoing problem."

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His comments come after West Auckland residents raised the rat alarm earlier this month, saying rodents as big as cats were wandering about Titirangi town centre, showing scant regard for shoppers.

Since then, infestations have been reported everywhere from Grey Lynn and Mt Albert to Mission Bay, leaving pest controller's phones ringing off the hook.

Barry said the booming rat population would happily move into any Auckland neighbourhood, but the leafier suburbs, close to rivers, parks and culverts were most desirable.

A rat and kereru egg. Photo / Nga Manu Nature Images
A rat and kereru egg. Photo / Nga Manu Nature Images

This was because rats preferred to live and breed outdoors in natural environments and then move indoors in winter in search of warm and dry haunts.

Rat populations have also exploded elsewhere across New Zealand, with some saying numbers are at a 48-year high.

Megan Hubscher from non-profit Forest & Bird said 2019 was what was called a mega mast year.

"[That] means our native trees are fruiting really heavily and normally that would have fed our bird population, but these days it's feeding rats," she said.

"We are seeing some really alarming numbers coming through from our trapping groups around the country."

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"I was sent a photo of a rat that was caught in Central Wellington and it was the size of a possum. I haven't ever seen a rat that big before, so there's certainly seems to be some correlation between a masting event and the size of rats."

Her comments echoed those of Titirangi residents, who joked the rats could even give local cats a fright.

But Barry from the Pest Management Association was keen to dispel the myth.

"They don't in reality get that big," he said.

"They just probably appear that big to most people because they don't see them that often."

A Titirangi resident's cat brought this rat into her home. Photo / Supplied
A Titirangi resident's cat brought this rat into her home. Photo / Supplied

Rats could grow to about 30cm from nose to tail and over winter grew a thicker coat that made them look bigger, he said.

Those gorging on the extra berries and edible plants might also look bigger.

But Barry said the overabundance of flowering plants was more an issue in rural areas than in Auckland.

He also praised Auckland Council's efforts to provide free bait to groups and residents setting traps for rats.

Brett Butland, the project director of Auckland Council-run Pest Free Auckland, said there were more than 1700 community or school groups in the city region involved in controlling pest animals or plants.

Predator Free NZ lists 70 pest control groups in Auckland and 56 in Wellington.

One project - the Eastern Bays Songbird Project - aims to have rat traps in a quarter of east Auckland's 30,000 backyards.

Forest & Bird's Hubscher said such measures were needed to protect defenceless native animals.

Baits and traps

• Poison is an effective way to control rodents and can be purchased from supermarkets and hardware stores. Always read and follow the instructions.

• Rat and mouse traps can also be used and are available from supermarkets and hardware stores too.

Removing food sources

• Store rubbish in secure metal or thick plastic containers with lids.

• Do not leave plastic rubbish bags outside overnight, if possible.

• Keep the inside and outside of your home clear of food scraps and rubbish.

• Do not leave extra pet food out.

Reducing their habitat

• Remove weeds, overgrown grass, rubbish and other materials that could provide hiding places for rodents.

• Secure any gaps or cracks in your home to stop rodents getting in.

(Source: Ministry of Health)