They have survived wars, epidemics and revolutions. Rats have accompanied humans for centuries, although almost always in the shadows and with a bad reputation. In fact, in Paris have become the unexpected protagonists of the recent elections for the city’s mayor; The different candidates deployed in their programs a complete catalog of proposals to reduce their populations, from greater cleaning to the use of dry ice or non-lethal traps.
Upon taking office as the new mayor, the socialist Emmanuel Grégoire, announced a series of measures, such as better cleaning of the streets, to guarantee a “right to beauty”in their own words, for the world’s first tourist destination. The city has been on alert since 2022, at which time it was estimated that the rat population was higher than the human population. Citizens have a special application called «Dans Ma Rue» (On my street), with which they can report the presence of rats, among other problems, and even attach photos as proof.
The case of Paris is not exceptional. In Rome it is estimated that there are between six and seven million rats; in Paris, between three and six million; and almost two million in Brussels. Also in Spain there are signs of increased rat activity in our cities. «We have indications of the rat population; There are statistics in cities based on the number of complaints they receive and some companies publish the number of services they perform. That is to say, there are indicators worldwide that support that behind these sensations of increased activity there is a growth in the rat population,” comments Manuel García, director of the National Association of Environmental Health Companies (Anecpla), who insists on the difficulty in having exact data on the number of rodents that populate the cities: «Maybe we should stop and reflect on whether more efforts should be made to carry out a census. If we census wildlife animals because they are in danger of extinction or in a vulnerable situation, why not do it with these animals, which have an impact on our health? “It is very rare that a rigorous census is carried out.”
In addition to the increase in activity, and as many headlines warn when they talk about “superrats” or “mutant rats”, these rodents are generating resistance to the majority treatments throughout Europe. Spain joined the trend of studying these mutations in 2022. The National Institute of Agricultural and Food Research and Technology (INIA) of the CSIC identified “genetic mutations that confer resistance to anticoagulant rodenticides in rat populations from 12 autonomous communities.
The intensive use of rodenticides is causing genetic resistance. «We published a scientific article in 2022 because the Ministry for the Ecological Transition asked us to investigate what was happening with rats in Spain, since in other EU countries and even worldwide, individuals were appearing with mutations that made them more resistant to anticoagulant rodenticides. In 2026 we are doing the study again. There are at least eight first and second generation active substances that can be used. These studies generate information to control these populations, see how it works and learn to control growth,” says Azucena Bermejo, INIA-CSIC researcher.
What species are there on the Peninsula? Well, there are two: the sewer rat (Rattus norvegicus) and the black rat (Rattus rattus). While the first moves through sewers and underground areas, the second is also called roof rat because it usually makes its burrows in roofs or trees, such as the base of an olive tree or the top of a palm tree. «The black rat is that of the bubonic plague, it has been in Europe for the longest time. It is native to the Indian subcontinent and is the most widely distributed throughout the world, because it has adapted remarkably to living with us. The sewer rat arrived later in Europe, at the end of the 18th century, and it is the one that gives us the most headaches today because it is more distributed, has a larger population worldwide and is more aggressive and capable of displacing its cousin,” comments the director of Anecpla. For her part, Azucena Bermejo clarifies: «Since 2018, the presence of black rats has been confirmed in Madrid and the center of the peninsula. For decades there were no records of their presence; It was limited to Levante in Spanish. “Either it was not in the center or it could be that we did not notice its presence.”
Rats act as mechanical vectors. In reality, the bubonic plague is caused by a flea that uses the rat as mere transportation. Here we remember that of the Middle Ages, but “there are still specific outbreaks in other regions of the world. They also transmit salmonella. However, the most dangerous disease is, for me, leptospirosis, a pathology whose incidence is increasing and which is transmitted through the urine of these rodents. “Historically it has affected livestock farmers the most,” says Manuel García, director of Anecpla. These days, the technician participates as a speaker at the annual Environmental Health Congress of the Canary Islands, where, among other topics, the increasing presence of vectors such as mosquitoes capable of transmitting diseases such as dengue, until now unknown in Europe, are addressed. «There is a combination of factors behind it, such as human globalization. We are moving and we are moving merchandise like we have never done before and, clearly, there is a risk that some animal from a region that is not ours arrives, adapts and, if it adapts, then there is a reservoir of new diseases. These diseases can also appear, even though we live in healthier conditions. We have seen it with bed bugs in France or Italy. And climate change also influences,” says Manuel García, from Anecpla.
Rat tourism
Increasingly milder winters are combined with the enormous volume of waste generated in cities. In fact, a recent publication in The Guardian newspaper states that this year New York City has seen rat populations decrease due to the severe winter that the city has suffered (in February the Big Apple was buried in half a meter of snow in a historic snowfall). “The city has spent years and millions of dollars trying to reduce the rat population,” says the outlet, which alludes to the increase in the number of containers – to prevent New Yorkers from abandoning bags directly on the street – and the appointment of a “rat czar”, a figure specialized in the control of these rodents that the mayor invented back in 2022.
It sounds like a joke, but through social networks you can find tourist routes on foot to see rats (walking rat tours) around the city. For about $45, John Kenny Bollwerk tours the city with groups of curious people who want to film or spot these animals. Users rate the experience with a 5 on Tripadvisor.
Integrated management
►In Europe, according to a media specialized in community politics, it is expected that a new biocidal regulation will appear in 2027. “The Center for Wild Animal Welfare, based in the United Kingdom, has asked the European Commission to explore ways to reduce fertility,” the outlet commented in a piece a few weeks ago.
The question that arises when thinking that rats are “getting stronger” is not something minor. Are there alternatives for managing these rodents? From Anecpla, its director, Manuel García, explains precisely that the trend in pest control is to use fewer chemical components. «Integrated pest management seeks to minimize the use of chemicals and also avoid resistance as much as possible. What he proposes is to use the chemical only if you are not able to avoid the pest with other measures: educational or physical, through traps; with biological control through predators or fungi. And, if you do introduce the chemical, what you have to consider from the beginning is to rotate. “You cannot always carry out the control in the same place with the same active material.” From the INIA, Bermejo advises equipping ourselves with mechanical traps in the event that we see a rat at home and leaving the active substances for the professionals who act at the city level. It also asks for collaboration for its new data collection campaign to city councils.