Red imported fire ants walk along stone.

Red imported fire ants originate from South America, and form large colonies which can include hundreds of thousands of individuals. Image © OMG_Studio/Shutterstock. 

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Invasive red fire ants found in Europe for the first time

One of the world’s most damaging invasive species has arrived in Europe.

Efforts to understand how the insects, known as red imported fire ants, arrived in the continent and how they can be removed are already underway.

An invasive species of ant has been discovered in Europe for the first time.

Nearly 90 nests of the red imported fire ant, or Solenopsis invicta, were found near the city of Syracuse, Italy, according to a new report published in the journal Current Biology. While the ants have occasionally been found in imported products in Europe, this is the first time they have become established in the wild.

With a painful sting and a voracious appetite, the ants are known to pose a risk to native ecosystems, farming and human health. Globally, it’s estimated that as much as $32 billion is spent every year to deal with the insects, a cost that will only increase if the ants spread to a new continent.

Mattia Menchetti, a PhD student who was the lead author of the new research, says, ‘Solenopsis invicta is one of the world’s worst invasive species, and can spread alarmingly quickly.’

‘However, despite the vast number of alien ant species establishing in Europe, the absence of this species came as a relief. However, we’ve always feared that it would arrive, and now this day has come. We could not believe our eyes when we saw it.’

While it might be possible to eradicate the fire ants before they spread further into Europe, there are concerns that climate change may help them to spread before they can be removed.

An aerial photograph of Mobile, Alabama with a port on the left and city on the right.

The ants are known to have invaded Mobile, Alabama in the 1930s through its port, and have since spread across the USA. Image © George Dodd III/Shutterstock. 

Where do red imported fire ants come from?

Red imported fire ants (RIFA) are native to South America, where a variety of insects, spiders and birds prey on them and help to keep their populations in check. When they spread beyond this region, however, they’re much harder to control.

The first red fire ants to establish outside of their home range are believed to have arrived in Mobile, Alabama, in the 1930s. It’s thought that soil containing the ants was used as ballast for the ships arriving at the port city, allowing the ants to gain a foothold in a new continent.

Since then, the ants have spread across much of the USA, where it is estimated they cost around $6 billion to deal with every year. Genetic studies of the ants have shown that the subsequent spread of the ant to countries including China, Australia and New Zealand all come from North American populations, likely through the shipping of contaminated goods.

What are the impacts of red imported fire ants?

Red imported fire ants have a painful sting, which they use to defend themselves and their colony. If a human or animal accidentally disturbs them, the ants will respond by injecting venom into the unfortunate victim.

For larger animals, including humans, a single sting is about as painful as a bee’s, and while it might cause a pustule to form around the wound it is otherwise harmless. However, in some people the sting can cause a severe allergic reaction which can be life-threatening if not treated quickly.

Smaller animals, such as birds, lizards and some mammals, are at much greater risk of serious harm from the ants, especially if the insects feel threatened. This can encourage them to release pheromones that cause them to swarm and sting in a group which can prove fatal.

The most prolific impacts, however, tend to come as the result of their relationship on much smaller animals.

Suzanne Ryder, the Senior Curator in Charge who looks after the Natural History Museum’s ant collections, says, ‘Arthropods like spiders and other ant species are a big source of food for the red imported fire ant.’

‘While some ant species can live alongside them, many can’t, and this means the fire ants have quite an impact on the ecology of the areas they live in.’

This can prove especially problematic if the ants move onto farmland. As well as threatening the wildlife which live there, they can also eat seeds and damage the shoots of young plants, leading to reduced yields for farmers.

Fire ants are also able to live in urban areas as they can build their nests under concrete and other artificial materials, which can cause structural issues with buildings. They are also known to attack electrical equipment after being shocked.

The collective impact of the ant meant that in the year 2000, the International Union for the Conservation of Species declared it one of the 100 worst invasive species in the world.

A foot covered in red stings from a red imported fire ant.

Red imported fire ant stings can cause pustules and red welts on the skin. Image © gob_cu/Shutterstock. 

Red imported fire ants in Europe

The team were first alerted to the possibility of red imported fire ants in Europe after they saw photos of what appeared to be S. invicta in Sicily. After travelling to Syracuse, they found 88 nests stretching over an area of 47,000 square metres – about the same area as a football stadium.

‘The locals have been experiencing these painful things since at least 2019, so the ants have probably been there for a while,’ says Mattia. ‘And the true extent of the invaded area is probably larger.’

While it’s not quite sure how the ants arrived in Italy, it’s likely to be similar to their other invasions where the insects arrived in contaminated plants or the holds of cargo ships. As the ants are currently found in an isolated nature reserve, the team believe they probably spread from a nearby port.

Genetic analysis of the ants’ DNA suggests that whatever their route of arrival, they probably came from the USA or China. While there are no indications of any further colonies being established, the scientists have recommended monitoring for the insects over a wide area of the island.

How do red imported fire ants spread?

Red imported fire ants spread following the nuptial flight, where new queens breed with males in the air before dispersing to found new colonies. After finding a suitable spot, the queens lay their fertilised eggs which hatch to become the first worker ants of the new colony.

‘These ants are quite prolific, with the ability to breed and spread rapidly when they’re in a suitable environment,' says Suzanne. 'They form exceptionally large colonies that allow them to quickly dominate other arthropod species.'

‘These colonies come in two kinds, monogynic and polygynic. The former just has one queen, while the latter is a large ‘supercolony’ containing several queens working together.’

Similar to other invasive populations of these ants, the Sicilian colonies are polygynic. While there are no signs of them spreading further at the moment, the team wanted to predict where new colonies could establish.

To do this, they created models of how suitable different areas of Europe are for the fire ants to live in. At the moment, around 7% of the continent is thought to be suitable, mostly in agricultural land and in urban areas such as London and Paris.

The most suitable areas, however, were found along the coastline of the Mediterranean. Many of these cities contain large ports, which could increase the possibility that the ant could spread more widely across Europe and the world.

By 2050, the model predicts that the climate crisis will make more of Europe suitable for the ants. Areas of Italy, Belgium and the Netherlands are likely to become ideal breeding grounds for the ants if they can reach them.

However, while the situation is a cause for concern, there is still time to deal with the ants before their populations spread out of control.

A red imported fire ant nest under a tree log near a river.

A red imported fire ant nest found in Sicily, one of 88 found by the researchers. Image © Institut de Biologia Evolutiva.

How can red imported fire ants be dealt with?

While red imported fire ants are a concern, they can be successfully controlled. Generally, the best option is to ensure they never get the chance to establish colonies in the first place.

‘These ants are seen as a threat by various countries, so a lot of work has been done to prevent their arrival,’ Suzanne says. ‘While insecticides are still used to eradicate RIFA in some countries, quarantining imported plants products and soil is the most important method of control.’

Though the ants are more difficult to combat once they have established in a country, it’s not impossible. New Zealand, for instance, has eradicated the species on multiple occasions using a combination of insecticide and population monitoring.

Other research has looked at the possibility of using the ant’s natural enemies as a control. The use of viruses, parasitoid wasps, ant-eating flies and parasitic fungi are among the methods currently being investigated for their potential to kill the ant without harming native species.

In Sicily, the researchers hope to build on previous experience and research to plan the eradication of the ants. This will begin with the systematic inspection of location areas to uncover any more RIFA colonies that might have been missed, followed by a multi-year treatment plan to eradicate the nests.

The nests will then continue to be monitored after the treatment ends to make sure that the ants have been completely eradicated.

To help with this, the researchers hope to get local Sicilians involved as part of a community science project to track the spread of the ants and raise awareness.

‘There needs to be more awareness about this problem, and we need coordinated action,’ Mattia says. ‘We hope that, with the help of local people, we will be able to cover a wider area and help us to spot all the possible areas the ants have invaded.’