Solenopsis invicta has officially arrived in Europe. This species, commonly referred to as fire ants, which is among the most invasive in the world, was discovered in the wild on European soil for the first time by a team of Spanish and Italian scientists, who report it in a paper published in the journal Current Biology on Monday , September 11.
“We initially received photos from a resident of the Syracuse region of Sicily who complained about being bitten by an ant, and the attached photos looked like fire ants,” says Mattia Menchetti, a researcher at the Institute of Evolutionary Biology in Barcelona and lead author of the article.
About 100,000 fire ants around Syracuse
At the end of 2022, he and his team traveled there to determine whether it was actually Solenopsis invicta, a brown-red ant, up to 5 mm long and equipped with an arrow feared worldwide.
There is no doubt: a total of 88 fire ant nests were found. Since we know that a single nest can easily contain more than 1,000 individuals, “we estimate that there must have already been around 100,000 ants in an area of 4.7 hectares,” says Mattia Menchetti.
* © Studio Graphique France Médias Monde
This first contact does not mean that the invasive species had just arrived on Italian soil. “Statements from locals suggest a presence that could go back to 2019, but we were unable to confirm this,” explains the evolutionary biology expert.
This confirmation of the presence of fire ants in Europe “raises concern when we observe the very negative impacts of this species elsewhere in the world,” says Olivier Blight, an invasive species specialist at the University of Avignon.
This tropical insect, native to South America, is ranked among the ten most harmful invasive species to humans in the latest reference report of the Intergovernmental Science and Policy Platform on Biodiversity and Ecosystem Services (IPBES), published in early September 2023.
Before Solenopsis invicta built its first nests in Europe, it spent a century largely at home in North America, Asia and Oceania. Its presence costs billions of euros every year, “both because of its direct impact on the economy and because of the expenses incurred in trying to eradicate it or contain its spread,” notes Olivier Blight.
If in their original habitat in South America these small ants encounter other species that have learned to defend themselves against them, this is not the case at all in the new regions where they settle. They have little competition and “cause devastating damage to local biodiversity by asserting themselves at the expense of other species,” emphasizes Mattia Menchetti.
Strong poison
These losses inflicted on biodiversity result in high economic costs, as the OECD highlights in a 2019 report. But the fire ant “also has a significant impact on health, as its stinger contains a strong poison,” points out specialist Gema Trigos-Peral in biodiversity and ants at the Museum and Institute of Zoology of the Polish Academy of Sciences.
“Not only is their sting very painful, but anaphylactic shock also occurs every year. [réaction allergique brutale, NDLR]“, adds this expert.
And it’s not just people who are affected. “These ants can seriously injure or even kill small livestock,” notes Gema Trigos-Peral. For this reason, agriculture and livestock farming are often considered major victims of their spread.
So there are many reasons to get rid of these invasive little creatures as quickly as possible. But success stories in this area are rare. The United States and Australia spend hundreds of millions of euros every year without managing to get rid of them. Only the New Zealanders managed to eradicate them, but “only because they did it in time,” emphasizes Olivier Blight.
In fact, this species can reproduce very quickly without being immediately blocked. On the one hand, it is a species of ant “capable of forming super colonies,” notes Olivier Blight. In most noninvasive species, two neighboring nests compete until one triumphs over the other. This is not the case with fire ants. “The energy saved in this way can be used for reproduction,” summarizes the specialist from the University of Avignon.
These super colonies can become very impressive. In the case of the Argentine ant – which is also found in Europe but is less devastating – there is one that stretches over 6,000 km.
On the other hand, Solenopsis invicta accepts the presence of multiple queens in a single nest, which is far from the case with most ant species. Again, it’s a fantastic population accelerator.
Finally, fire ants can also spread naturally over several kilometers. This means that they do not necessarily have to be transported by people to ensure their spread. This is due to the queens performing their nuptial flights while mating in the nest of other species. This allows the “Fire Queens” to lay their eggs miles away from their original lair… and find a new nest there.
When this species is discovered, a race against time begins because “it is a classic case of a situation in which inaction costs more than action,” assures Olivier Blight.
In the city while waiting for global warming
Europe long believed it was safe from invasion by these tropical insects, which require a warmer and wetter climate to survive than that prevailing in much of the old continent. But due to global warming, there would now be 7% of European land where the fire ant could thrive, and almost 50% of urban areas, including cities like Paris and London.
However, the experts interviewed by France 24 assure that we should not blame everything on global warming. “The arrival in Europe is primarily due to the globalization of trade – fire ants usually arrive on merchant ships – and global warming only makes their settlement easier,” explains Mattia Menchetti.
For his part, Olivier Blight specifies that cities represent the “bridgeheads” of the spread in regions that are not yet climatically acceptable for these tropical insects. In fact, urban centers represent suitable “microclimates” for these ants: when it is too cold in winter they find refuge in buildings, and when summer is too dry for their liking they just need to find pockets of moisture. All you have to do is wait between two buildings until global warming turns all of Europe into a playground.
In this respect, it is probably “lucky that the first nests were discovered on an island like Sicily,” says Gema Trigos-Peral. There are fewer large urban centers and water can slow natural spread. “If the presence in Europe is limited to this area, eradication with pesticides is still entirely possible,” believes Olivier Blight.
However, it is still necessary that the outskirts of Syracuse truly represent the beginning of the European adventure for this invasive species. “When we hear about the stings of these ants, it is usually because they have been there for a while,” says Gema Trigos-Peral. They probably then had time to expand their domain.
Above all, “it is actually not the first time that we have seen fire ants in Europe,” affirms Olivier Blight. These have been observed in shipments of exotic plants arriving at ports, particularly in the Netherlands. Each time they were intercepted.
But some may have gone unnoticed. In this case, the discovery of Syracuse would be more of a confirmation. However, it is urgent to know what to do: is there still time to eradicate the insect or should we, above all, try to contain its spread? For this, according to Mattia Menchetti, it is essential to “appeal to the population” by asking them to report their stings and to send any photo of an ant that looks reddish or suspicious.