In 2019, people living near the city of Siracusa, in southeastern Sicily, began reporting painful stings from ants in 2019. In November 2022 a man sent a picture of one of these ants to his friend, Antonio Alicata, an ant expert who collaborates with the University of Catania. Now a study in Current Biology1 by researchers, led by Roger Vila, of the Institut de Biologia Evolutiva (IBE) in Barcelona, and including Alicata, confirms that the ant belongs to the species Solenopsis invicta.
Commonly called the red fire ant, it is the fifth most damaging invasive species in the world in harm wreaked on the environment, agriculture, and human health. It can destroy crops, outcompete other insects, cause structural damage to buildings, and its painful sting can be dangerous for humans. “The need for an eradication campaign is urgent”, says Mattia Menchetti, first author of the study and PhD student at IBE.
Researchers found 88 nests spread across an area of five hectares. In mid-August 2023, a new observation was uploaded on iNaturalist, the citizen science platform, reporting a suspected red fire ant in a coastal area nearly six kilometers south of the infested zone.
The authors drew in all the available data to obtain a habitat suitability map, which shows that currently in 7% of Europe and the Mediterranean temperatures and soil properties would support the pest’s invasion. Considering climate change, this fraction could increase to 25% in 2050.
The social organization of red fire ant colonies may be one of the keys to their success as an invasive species. “Each colony has several queens that can fly, exploiting winds to facilitate the population dispersion”, explains Menchetti.
Further, ants belonging to different colonies do not compete, as with many other ant species. “The nests we found form a single supercolony, with a dense population that can exert a high toll on the biodiversity of the area,” says Enrico Schifani, a PhD student at the University of Parma, and co-author.
In their native habitat in South America, red fire ants do not exhibit this cooperative behavior across colonies. They developed it invading other territories, such as the United States. “It may have been favoured because of the lower genetic variability of imported populations, that originated from very few individuals”, Schifani observes.
Genetic analyses indicated that the United States, China and Taiwan are the three most probable introduction sources. Ships arriving from these locations could have carried the ants to the port of Augusta, less than 20 kilometers north of Siracusa.
The researchers have alerted regional authorities, which are now required under EU regulations to tackle the problem. Eradication has been accomplished in the past, in some parts of Australia and New Zealand. “The successful eradications there were mainly in ports, which are an easier setting to work in,” says Menchetti.
In Australia, where two eradication campaigns are underway outside ports, members of the public are asked to monitor gardens, report suspected ants, and carry out insecticide treatments. “Eradication efforts will largely depend on the institutions’ ability to engage with citizens and obtain their cooperation,” says Menchetti.