The social insects that become even more social away from home

There's a curious story going the rounds about a super-colony of ants in Melbourne, Australia. It's being described as a single colony 100 kilometres across.

Ranked amongst the top 100 of worst invading species, these ants arrived from Argentina in the 1930s. They usually exist in smaller groups but in Australia have merged to form one massive colony that is thought to threaten the area's biodiversity.

Elissa Suhr, from Monash University, Melbourne, said the introduced pest's natural aggression kept numbers under control in its native country.

But the lack of genetic diversity in the ants found in Australia has allowed them to build a super colony.

"In Argentina, their native homeland, ant colonies span tens of metres, are genetically diverse and highly aggressive towards one another," Dr Suhr said.

"So population numbers never explode and they are no threat to other plants and animals.

"When they arrived in Australia, in 1939, a change in their structure occurred, changing their behaviour so that they are not aggressive towards one another. This has resulted in the colonies becoming one super colony."

The ants have also been found in California.