James Randerson, guardian.co.uk 3 Dec 08;
An ant species that forms huge supercolonies and infests gardens and parks is marching rapidly across Europe and will soon invade the UK, according to entomologists who are monitoring its spread.
The colonies can swell to 10 or 100 times the size of those of common garden ants and scientists warn that they can cause significant damage to plants.
"When I saw this ant for the first time, I simply could not believe there could be so many garden ants in the same lawn," says Prof Jacobus Boomsma at the University of Copenhagen, one of its co-discoverers almost 20 years ago.
"We reckon it's only a matter of time before [it invades the UK]."
The invasive garden ant or Lasius neglectus was first identified in 1990 when it was found infesting an entire neighbourhood in Budapest, Hungary.
"This ant basically looks like the garden ant that everybody knows, so you don't really become suspicious if you see a few of those crawling around because they are everywhere," he said. It has since become a major pest in central Europe and has spread as far as Jena in Germany, Ghent in Belgium and Warsaw in Poland.
Boomsma and his team think it is moved around by the horticultural trade because it hides inside plant pots. "That is the most reasonable hypothesis for how these ants get transported because the ants themselves have lost the ability to fly so they are very poor disbursers," he said.
In research published today in the journal PLoS One, the team used genetic techniques to work out where the ants originated and what makes them so successful at taking over new regions. One reason is that they are able to form super-colonies.
The ants occupy many interconnected nests with many queens. Because they are related, the ants in these nests do not show territorial aggression. When they reach new locations the parasites that usually keep the ants in check are no longer there, so they are able to expand their colonies rapidly.
"We found that invasive garden ants developed from species in the Black Sea region that have natural populations with small networks of interconnected nests with many queens that mate underground and don't fly.
"It is now becoming clear that rather many ant species share this lifestyle, so it is no surprise that a number of them have become invasive pests with giant super-colonies based on the same principles," said Dr Sylvia Cremer, at the University of Regensburg.
Dr Jes Pedersen, a co-author at the University of Copenhagen, said: "The future will therefore see many more ants become invasive, so it is about time we understand their biology. This study is a major step in that direction."
Much of the damage that the invasive garden ant causes is connected with the herds of aphids that it tends. The ants have a symbiotic relationship with the aphids in which the aphids provide sugary food while the ants provide protection from predators.
With the ants around, aphid populations expand to large numbers causing damage to plants and releasing sticky secretions that create a mess on parked cars. Because the ant colonies are so large they can cause a nuisance by invading homes and spoiling food.
Invasive ants have caused much more significant damage in other countries. The imported red fire ant, which has a nasty sting, causes $750m (£500m) of damage in the US each year to crops and livestock. The Argentine ant has spread along 6,000km of coastline in southern Europe, exterminating many local insects.
