Fears are growing that Ireland's rat population has exploded, as pest control experts report the number of vermin-infested households across the country has soared to unprecedented levels.

Pest controllers have noted an unusual surge in the number of call-outs for rodent-infested homes over the summer months, with as many as four out of five jobs over the season being rat-related.

The problem has become so widespread that in recent weeks some pest control companies ran out of specialist equipment and supplies to tackle rat infestations.

Experts believe the sharp spike in vermin-related cases is due to a combination of increased building work, a rise in fly-tipping and the mild weather of last winter.

Trevor Hayden, who runs nationwide company Complete Pest Control, said his team has been tackling multiple rat-infested households every single day this year, the first time this has happened.

"In the past rats have generally been a problem for householders mainly in the winter months, but this year there has been no let-up at all since the start of the year, and that's something that's never happened before,” he said.

"We've had rat jobs every single day of the year and over the summer months we've been getting between 15 and 20 calls a day for rats, which represents about 80 percent of our business. You'd normally expect ants and wasps to be the dominant pest in summer, but this time it's been rats that have been causing most havoc.”

Hayden, who works with the Campaign for Responsible Rodenticide Use, has previously voiced his concerns about the increased size of rats, caused by rodents growing immune to conventional poison.

He said he believes the spread of vermin in Irish homes has been accelerated by failed home treatments which have helped rats grow bigger and stronger, as well as building up their immunity.

Ireland's rat population has exploded. As many as 4 out of 5 jobs for Pest controllers this season are rat-related.Getty Images/iStockphoto