PARIS — It all started with a video shot late last year on the banks of the Seine, between the Musée d'Orsay and Pont Royal bridge in the French capital. The video, which has gone viral around the world since first being posted by the daily Le Parisien, shows garbage collectors discovering with horror dozens of hungry rats crawling at the bottom of a garbage bin. The footage kicked off a controversy over the "proliferation" of rats in Paris, and the deplorable working conditions of the city's garbage collectors.

There are now between 4 and 6 million rats in Paris, according to different sources. "But in reality, it's impossible to know precisely how many of them there are," says Georges Salines, who heads of the city's environmental health service. "Their number varies according to the amount of food available and their living conditions. Rats are complex social animals that can stabilize their population according to vital resources. That's why I think it's wrong to talk about a proliferation of rats in our city. Despite the appearances, their population remains stable."

The swollen Seine, bursting its banks after weeks of rain, has made things even worse.

And yet, for several months now, in the early morning or as soon as night falls, alone or in small groups, rats seems to be more abundant and less and less fearful. They leave their holes in search of food, sometimes in front of passers-by. They gather around garbage cans, criss-cross grassy areas in the city's parks, and scramble around the Champs-Elysées and in the streets where open-air markets are held. They can even be seen in the square in front of the Notre Dame cathedral, much to the dismay of tourists, who much prefer the friendly cartoon rats of Disney's Ratatouille to the real flesh and blood variety.

The swollen Seine, bursting its banks after weeks of rain, has made things even worse. "Their burrows on the river banks and in the sewers were flooded and many colonies were forced to migrate elsewhere. But it doesn't mean they've invaded Paris," says Pierre Falgayrac, a rat specialist and author of several books on the topic. Just because the rats or more visible, in other words, doesn't mean they're more numerous.

"We should even expect to see increased mortality and reduced reproduction in the near future," Falgayrac predicts. "What's more, major construction products in Paris — the expansion of the tramway, for example — keep driving them out of their holes, and their population is constantly weakened. This, in my opinion, could explain the sporadic concentrations of hungry and unusually aggressive rodents we're currently seeing."

The specialist says that under normal circumstances, sewer rats are quiet and timid animals that spend the most of their time hidden and only come out of their burrows to eat and drink. "The real problem, in my opinion, is the risk that they could provoke electrical accidents," Falgayrac explains. "European standards now require that the plastic sheathing traditionally used to cover electric cables be replaced with materials made from corn starch, which rodents love. The situation ought to be taken very seriously."

Signs near the Eiffel Tower warn people about the risks of leaving garbage on the ground Photo: Danielle Shields/Facebook

Even before the now-famous rat video made the rounds, mayors in some of the city's arrondissements chided what they called a lack of action on the issue and called for a Paris-wide crackdown on the rodents. Adding to the sense of concern is a study carried out by INRA, VetAgro Sup and the Pasteur Institute suggesting that some rats have become "genetically resistant" to the poisons used to control their population. Researchers believe that by regularly consuming the anticoagulant products, but in small doses, rats are gradually developing an immunity.

"Above all, city authorities should eliminate rats from future construction sites before work actually begins. That way they prevent the rats from moving elsewhere," says Falgayrac. The specialist also advocates filling up some sewers with concrete, particularly ones that are in areas with lots of restaurants, and requiring restaurateurs to clean up their terraces in the evening, before closing, rather than in the morning.

"Similarly, garbage cans should not stay on the sidewalks for too long," he adds. "But let's not forget that rats are also allies for the sanitation services — provided that their numbers are under control — since they prevent certain sewers from clogging up."

A centuries-long invasion

Rats are right up there with spiders and snakes on the list of animals we humans most despise. They remain linked, in our collective consciousness, to the black plague that devastated medieval Europe, and according to a the INRA/VetAgro Sup/Pasteur Institute study, rats are hosts to at least "eight species of worms, three species of fleas, one protozoan and four bacterial geni." The parasites include tapeworms, the tularemia germ, and bacteria responsible for leptospirosis. We also think of them as fierce, aggressive animals, and associate them with darkness and the abyss. Indeed, they seem to come straight out of hell.

The black rat (Rattus rattus), also known as the roof rat or house rat, is still considered to be one of the main carriers of plague in Africa and Central Asia. In Europe, though, it was gradually replaced from the 18th century onwards by the brown rat (Rattus norvegicus), also known as the sewer rat — the same species that now proliferates in our cities.

A petition entitled 'Stop the Rat Genocide' launched in 2016 gathered more than 25,000 signatures.

Originally from Asia, brown rats spread throughout Europe starting in the 9th century, courtesy of infested ships used for Viking expeditions. Present on all continents except Antarctica, the brown rat likes to live in contact with humans, who provide shelter and food in abundance. An extremely prolific nocturnal and omnivorous animal, and organized in highly hierarchical groups dominated by alpha males and older females, it nests mainly in sewers and subway tunnels, which provide large nesting areas protected from predators — and humans.

"We are well aware that it is impossible to totally eradicate rats," explains Georges Salines. "This is why we have adapted our de-ratization methods together with all the Parisian arrondissements. Our main goal is to prevent rodents from coming out of the sewers, to eliminate them in the basements of the buildings where they nest, to fill up their burrows, and to continue to place secure boxes of anticoagulant bait in green spaces."

The other key, according to the city official, is raising public awareness: convincing people to clean up after themselves, to put garbage where it belongs and not leave food scraps behind in picnic areas, for example.

Regardless, the brown rat is well established in Paris, where the brick sewers, which it can easily gnaw into with its teeth, allow it to dig cozy burrows. Moreover, some Parisians seem to have a strange relationship with their rodent neighbors. A petition entitled "Stop the Rat Genocide" launched in 2016 gathered more than 25,000 signatures to protest against "the extermination being carried out by the authorities."

Go figure. Sometimes things are so complicated you can't make head or tail of it.

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