Animal welfare campaigners are urging EU leaders to seek new approaches to exploding rat populations, as growing resistance to traditional poisons leads to the use of ever more toxic chemicals.
The pesky rodents are estimated to number around seven million in Rome, between three and six million in Paris, and nearly two million in Brussels. They are increasingly found in basements and parks, scurrying along drains, around rubbish bins, and foraging in alleys behind restaurants.
Their proliferation has been attributed in large part to global warming, with milder winters meaning easier access to food and a longer breeding season.
Once a vector for the terrifying plague, rats are still linked in many minds with squalor and dirt and now provoke disgust rather than posing a significant public health threat.
Still, the growing feeling that something needs to be done has focused attention on the EU’s Biocidal Products Regulation (BPR), which is currently under review, and could offer a pathway to better control their populations.
Birth control
A public consultation closed last week, and a proposal to revise the regulation is set to land before the middle of 2027. The UK-based Centre for Wild Animal Welfare called this week for the European Commission to explore ways to reduce fertility, blaming “sluggish regulation” for Europe’s lack of progress compared to the US.
“There is plenty of room for innovation for safer and more effective alternatives,” Ben Stevenson of the Center for Wild Animal Welfare told Euractiv. “There are many other routes to restrict rodent fertility, and we think these are worth exploring as humane alternatives”.
What’s more, poison programmes don’t work anyway, Stevenson said. As well as being inhumane – conventional anticoagulants like warfarin induce internal bleeding and taking a week or more to kill a rat – there is a growing body of scientific evidence that rats are developing genetic resistance.
These traditional poisons are persistent and bioaccumulative, posing a serious environmental pollution risk. Moreover, they kill species like owls, hawks and foxes – and domestic cats and dogs – that might otherwise help control rodent populations.
Any temporary decline in population causes rats to reproduce at maximum capacity to fill the sudden excess of food and territory available to them. Populations of ‘super rats’ – genetically resistant to the most commonly used chemicals – are already proliferating in cities across Europe and around the globe.
Fight back
In Brussels, the Belgian and EU capital, the city government launched a task force to combat rats in early 2025. More than 1,358 extermination operations have been carried out since then, according to the news website DH. But experience suggests populations will bounce back.
Contraceptives have the advantage of slowing population growth by rendering rats infertile without killing them. “We therefore believe that fertility control is the most promising approach, as it takes into account animal welfare, the environment, and human health,” Stevenson said.
The problem, he says, is that under existing European regulations, these non-lethal, non-toxic contraceptives are subject to “the same rigid, slow, and expensive testing frameworks designed for highly toxic, lethal chemicals, effectively blocking market entry”.
Rodent fertility control methods take the form of sweet liquid baits that rats voluntarily drink. These products disrupt the reproductive system of females by naturally depleting ovarian follicles and, in males, altering sperm development and motility.
According to CWAW, ContraPest, a rat contraceptive approved in the US since 2016, has a key advantage because its active ingredients break down rapidly in rats into inactive, non-toxic compounds.
“As these fertility control products are very new, they have been classified as biocides,” Stevenson told Euractiv. “The dedicated regulatory pathway could either be within the biocidal products regulation or in a separate product category.”
“European cities, like Barcelona with pigeons, already use fertility control for other wild animals,” Stevenson said. “This proves that there’s enough interest in major cities”.
A political issue
In Paris, where the rat question has made its way into the manifestos for the municipal elections, scheduled for 15 and 22 March, where candidates frame the problem squarely as one of cleanliness.
The far-right candidate and MEP for the Europe of Sovereign Nations Group, Sarah Knafo, writes, for example, that “the proliferation of rats is simply the result of filth”.
Far-left candidate Sophia Chikirou and right-wing candidate Rachida Dati also address the issue from the perspective of urban hygiene and waste management.
While Chikirou believes that the methods used should be “respectful of animal welfare”, none of the candidates mentions the use of contraceptive techniques.
In any case, the use of birth control chemicals will be dependent on their authorisation at the European level.
With clear evidence that global warming is contributing to a population explosion – Amsterdam made headlines last year when a scientific study ranked it just behind New York – European cities, and especially their leaders, are likely to face increasing pressure to bring rat populations under control.
(jp, rh, aw)
