Solenopsis invicta has officially arrived in Europe. Commonly known as fire ants, this species among the most invasive in the world was detected for the first time in nature on European soil by a team of Spanish and Italian scientists, who report it in an article published by the journal Current Biology on Monday, September 11.
"We first received photos of a resident of the Syracuse region of Sicily who complained of being bitten by an ant and the attached photos looked like fire ants," says Mattia Menchetti, a researcher at Barcelona's Institute of Evolutionary Biology and lead author of the paper.
About 100,000 fire ants around Syracuse
He and his team then went there at the end of 2022 to determine if it was indeed Solenopsis invicta, a red-brown ant, up to 5 mm in size and with a stinger feared around the world.
No doubt: a total of 88 fire ant nests were found. Knowing that a single nest can easily have more than 1,000 individuals, "it is estimated that there must have already been about 100,000 ants on an area of 4.7 hectares," says Mattia Menchetti.
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This first contact does not mean that the invasive species had just put its paws on Italian soil. "Testimonies from locals suggest a presence that could date back to 2019, which we have not been able to confirm," says this specialist in evolutionary biology.
This confirmation of the presence of fire ants in Europe "is worrying when we observe the very negative impact of this species elsewhere in the world," says Olivier Blight, a specialist in invasive species at the University of Avignon.
Native to South America, this tropical insect is ranked in the top 10 most harmful invasive species for humans, in the recent landmark report of the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) published in early September 2023.
Before making its first nests in Europe, Solenopsis invicta has largely taken its ease, for a century, in North America, Asia and Oceania. Its presence costs billions of euros every year "both because of its direct impact on the economy and in spending to try to eradicate it or control its proliferation," notes Olivier Blight.
If in their original habitat in South America, these little ants face other species that have learned to defend themselves against them, this is not at all the case in the new regions where they settle. They encounter little competition and "wreak havoc on local biodiversity by imposing themselves at the expense of other species," says Mattia Menchetti.
These losses to biodiversity entail high economic costs, as highlighted by the OECD in a 2019 report. But the fire ant "also has an important health impact because of its stinger which contains a powerful poison," says Gema Trigos-Peral, a specialist in biodiversity and ants at the Museum and Institute of Zoology of the Polish Academy of Sciences.
"Their sting is not only very painful, but every year there are cases of anaphylactic shock [sudden allergic reaction, editor's note]," adds this expert.
And humans are not the only ones concerned. "These ants are capable of seriously injuring or even killing small livestock," notes Gema Trigos-Peral. This is why agriculture and livestock are often seen as major victims of their proliferation.
So many reasons to try to get rid of these little invasive beasts as quickly as possible. But success stories in this area are rare. The United States and Australia spend hundreds of millions of euros a year without managing to get rid of them. Only the New Zealanders managed to eradicate them, but "only because they did it in time," says Olivier Blight.
Indeed, this species can proliferate very quickly without prompt action to block its way. On the one hand, it is a type of ant "capable of forming supercolonies," notes Olivier Blight. In most non-invasive species, two nearby nests compete until one triumphs over the other. This is not the case with fire ants. "The energy thus saved can be used to multiply," summarizes the specialist of the University of Avignon.
These supercolonies can become very impressive. In the case of the Argentine ant - also present in Europe but less devastating - there is one that extends over 6,000 km.
On the other hand, Solenopsis invicta accepts the presence of several queens in a single nest, which is far from being the case in most ant species. Again, it is a formidable accelerator of settlement.
Finally, fire ants can also disperse naturally over several kilometers. That is, they do not necessarily need to be transported by humans for their spread to be assured. The fault lies with queens who make nuptial flights, while in other species they mate in the nest. Thus, the "queens of fire" can go laying eggs miles from their original lair... and build a new nest on site.
When this species is detected, it is therefore a race against time because "it is a classic case of situation where inaction costs more than action," says Olivier Blight.
In the city while waiting for global warming
Europe has long believed itself safe from an invasion of these tropical insects that would need, to survive, a climate warmer and wetter than that which dominates over a large part of the Old Continent. But, due to global warming, there would now be 7% of European lands where the fire ant could feel comfortable, and nearly 50% of urban areas, including cities like Paris or London.
But the experts interviewed by France 24 ensure that we must not blame everything on global warming. "The arrival in Europe is above all due to the globalization of trade - fire ants usually arrive by commercial boat - and global warming only facilitates their establishment," says Mattia Menchetti.
For his part, Olivier Blight specifies that cities represent the "bridgeheads" of proliferation in regions that are not yet climatically acceptable for these tropical insects. Indeed, urban centers are "microclimates" suitable for these ants: when it is too cold in winter, they find refuge in the building, and if the summer is too dry for their taste, they just have to find pockets of moisture. All they have to do is wait between two buildings for global warming to turn the whole of Europe into a playground.
In this respect, it is probably "a chance that the first nests were discovered on an island like Sicily," says Gema Trigos-Peral. There are fewer large urban centres and water can slow the natural spread. "If the presence in Europe is limited to this area, eradication based on pesticides is still quite possible," says Olivier Blight.
But it is still necessary that the surroundings of Syracuse are really the beginning of the European adventure for this invasive species. "Generally, when you start hearing about the bites of these ants, it is because they have already been there for some time," says Gema Trigos-Peral. They probably had time to expand their domain.
Above all, "this is not actually the first time we have seen fire ants in Europe," says Olivier Blight. These have been seen in shipments of exotic plants arriving in ports, including the Netherlands. Each time, they were intercepted.
But some may have gone unnoticed. In which case, the discovery of Syracuse would be more of a confirmation. But it is urgent to know which foot to dance on: is there still time to eradicate the insect or should we try to control its spread? For this, it is essential, according to Mattia Menchetti, to "appeal to the populations" by asking them to report their bites and to send any photo of ants with a reddish or suspicious look.
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