The Asian species Lasius neglectus is resistant to domestic ant treatments and has a fatal attraction to electricity.
A colony has been discovered at the National Trust's Hidcote Manor Gardens in Gloucestershire.
It is the first UK recording of Lasius neglectus, known as the Asian super ant, which is believed to have migrated from the Black Sea area, gradually spreading across Europe over the past 20 years. One colony recorded in Warsaw, Poland, covers more than 4ha.
Like the American fire ant, Lasius neglectus ants are attracted to electricity as the current makes them produce a pheromone which attracts other ants.
According to English Heritage entomologist and senior architectural conservator Brian Ridout, the compulsion to follow it is stronger than their need for food and drink.
This can create fire hazards as thousands of the ants congregate and die close to electrical sources.
The species was first identified in Budapest 20 years ago. It looks just like a black garden ant and as a result may have gone unrecognised at Hidcote for decades.
Ridout said: "The behaviour of the ants didn't agree with that of any known UK species. Our suspicions were confirmed when samples were sent to the Universitat Autonoma de Barcelona, which has been studying major infestations of them in Spain. They look just the same as the common black garden ant although there will be 10 to 100 times as many of them. Where they differ dramatically is in their behavioural patterns, in particular their social structure within the colony."
The super ant can form super colonies with many queens and interconnected nests stretching over up to at least a hectare.
The queens can breed with males from their own nest quickly and set up self-sufficient nests even when separated from the main colony.
The species is highly dependant on aphid honeydew and is associated with a wide range of tree species.
The trust estimates there were almost 35,000 ants in one electrical junction box based on the weight of the dead ants.
Nature conservation adviser for the National Trust in Wessex Simon Ford said: "The ants themselves pose little direct threat to us as they don't bite people or pets, but their habit of creating super colonies means they pose a threat to native species by out-competing them for food and space, and their attraction to electrical circuitry means they could pose a fire risk.
"Researchers have feared for several years that this species would make it to the UK, and while the Hidcote colony is the first case recorded, it's not clear if it is the first in the UK or indeed that it's the only one. It's very likely the ants are more prolific."
It's believed the Asian super ant is most often moved from site to site through plants and plant pots. Speculation has attributed the European spread to ants moving with plants and pots from Turkey.
The ant has so far proven to be resistant to domestically available treatments.
The National Trust is now considering how to tackle the colonies and is working with Bayer to investigate options; among them are bait systems and controlling aphids — the ants' food source.
Anyone who suspects they have an infestation of the Asian super ant should contact their environmental health departments within their local authority.
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