The number of reports of rats in Denmark has increased by 20,000 over the past five years – yes, there are people whose job is to count that sort of thing – and that number could grow dramatically come the autumn.

A mild winter, warm spring and hot summer have combined to make conditions perfect for a rat explosion.

“The mild winter means that instead of starting spring with fewer rats, there were still many around,” Claus Schultz, a technician at the pest removal company Rentokil, told Metroxpress. “They can start breeding earlier, and rats produce eight to ten offspring per litter.

Schultz said that the rats are staying out of sight for now, but will become a more visible problem at the first frost.

Rats not flushing
It is impossible to know exactly how many rats there are in Denmark, but indications are strong that the number is rising rapidly, according to the nature agency Naturstyrelsen, which recorded a total of 150,000 reports of rat sightings last year.

One of the councils hardest hit by the rodent explosion is Furesø in north Zealand. Reports of rat sightings by local citizens increased by 174 percent between 2009 and 2013.

“Our sewer workers say that low flush toilets are part of the problem,” Furesø Council's public amenities operations head Gert Klausen told Metroxpress. “Waste stays in the sewers longer and the rats feed on it and get stronger.”

The city with the highest number of rat reports is Copenhagen, with over 5,000 reports last year alone.