Invasive 'smelly' ants spark concern across France

Concern is growing in France about an invasive ant, called tapinoma, which can cause damage to farms, homes, gardens and equipment, as well as biting humans.

The little black ants can be distinguished from others by their smell – they smell like rancid butter when crushed.

There are four sub-species of tapinoma, all originally from around the Mediterranean, but they cause problems when they move from their original territories.

“It is the great number of ants in a colony which is the problem,” Dr Jean-Luc Mercier, of the Institute de la recherche sur la biologie de insecte at Tours University, told The Connexion.

Read more: PHOTOS: Ants take over home in south-west France

Mass invasion

“They live in the ground and are able to eat just about anything, so in market gardens and fruit orchards they cause damage to roots, the plants and crops.

“In urban and peri-urban areas, there are so many that people are not happy in their gardens because of ants running over them and because the ants can bite – it is not a poisonous bite but still not very pleasant.

“In homes too, as well as being a problem in kitchens, the ants have been known to eat their way through electric cable insulation, and even fibre optic cables, destroying connections and increasing the risk of fires.”

He warned that although the health risk from ants was not great, care must be taken around hospitals to ensure they are kept away from medical waste containing pathogens.

Municipal waste disposal services should also be vigilant to prevent sorting centres from being invaded and to make sure they do not hasten the spread of the ants.

Other damage ants can cause in urban areas is to roads, and to infrastructure such as water and gas pipes.

Read more: Giant 800-metre ant colony beneath beach in the south of France

Queens rule

The ants have been in mainland France for at least 20 years, mainly in isolated colonies including in parts of Bordeaux, Albi, Saumur, and Strasbourg.

It is thought soil in pots from garden centres was the main factor in their spread.

In Saumur (Maine-et-Loire), one of the main areas of focus in Dr Mercier’s research, tapinoma magnum ants have established themselves over a 19-hectare area in one of the suburbs.

“They are difficult to eradicate because each colony has numerous queens, as many as a thousand, so you can never be sure you have destroyed all the queens,” he said.

“Old methods like finding the entrance to a nest and pouring boiling water down do not work well because with tapinoma there are multiple holes for ants to come in and out of.

“And if you try to use poison you also have problems. You might kill off some of the queens but the others will still be alive and breed more ants, this time with a stronger resistance to the poison.”

Invasive ant research

In Saumur, Dr Mercier and teams from other local government agencies are trying to better understand how the ants spread and the risks they pose.

“For termites, there are strict protocols to be followed, which have limited the problem,” he said.

“But for ants there is nothing, mainly because until now there has been very little research on invasive ants.”

In Corsica, the invasive ants have caused significant falls in crop yields, and in mainland France Dr Mercier has also received calls for help from farmers, both because of invasions in farm buildings, but also because of their effects on crops.

“Where crops are grown through plastic, such as melons and strawberries, they are a particular problem, because under the plastic it is warm and humid – ideal conditions for ants,” he said.

“In general, however, we have realised that the ants thrive where biodiversity has been weakened, and increasing biodiversity – so they have less space to establish themselves – is the best way forward.”