Natural aggression kept numbers under control in the ants' native country

The ants, which were imported from Argentina, are ranked among the world's 100 worst animal invaders.

Although they exist in their usual smaller group size in their homeland, the colonies have merged in Australia to create one massive super colony.

Experts fear that the invasion poses a threat to biodiversity in the area.

Introduced pest

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."

Dr Suhr said the Argentine ants have killed native ants, and consumed many other insects, posing a major threat to biodiversity.

Taking over

She said Argentine ants could even displace native species by taking over local habitats and preying on insects commonly eaten by Australian ants.

Australia is not the only country to be invaded by Argentine ants, according to Dr Suhr.

"In California, they have displaced native ants, decreased the diversity of other native insects, affected the dispersal of seeds and even decreased lizard numbers," she said.

Australian scientists are studying colonies in Perth and Adelaide to see if they share the same genetic structure and behaviour as the Melbourne ants.

If they do, a super colony several thousand miles wide could spread across southern Australia.

Your comments

I live in Melbourne, and was unaware that our local ant problem had reached such behemoth proportions. For several months now, ants have had the run of our property, invading everything from the downstairs kitchen to the upstairs bathrooms. Thick black trails of insects are now a common site in every room of our abode, something that had never happened until the beginning of this year. I thought this problem was localised and was shocked to find out that the colony spread out over 100kms.
Anthony Hill, Melbourne, Australia

We have them in the wine area of Barossa Valley and once in the house they are worse than white ants. Ant trap poisons have limited effect.
Graham York, Nuriootpa, South Australia, Australia

We live in a house very close to the city centre in Melbourne, and we have certainly noticed an increase in the number of ants during the last year! They appear in odd places, even where there doesn't appear to be anything for them to eat there. If some food does get left out accidentally, then within a short period there will be a swarm of ants.
Douglas, Melbourne, Australia

I'm not from Melbourne but Perth, Western Australia and I live in a residential block of 8 units and I've noticed them on our property for the past 12 months. Their nests are everywhere. You can always tell an Argentine ant by their small size and the fact that when you crush them they do not leave behind that characteristic "ant" smell. They are incredibly invasive as you will find them in their hundreds on your kitchen side. I have also noticed that the other native ant colonies that were around are no longer so.
Gavin, Perth, W.A.