Bad attitude ants

[Aussies-Online]

Scientists describe it as a case of ecological meltdown.

The yellow crazy ants that invaded Christmas Island not only decimated its famous population of red land crabs by spraying formic acid into their eyes and then devouring millions of them.

The tiny ants also caused a cascade of events on the island that led to the death of rainforest canopy trees within only two years, new research shows.

Dennis O'Dowd, one of the authors of a study on the devastation, said it showed how an invader could alter an entire ecosystem. "This is one bad ant."

Earlier this year, infestations of crazy ants were discovered on the mainland, in Arnhem Land, raising fears they could spread across Australia, devastating communities, forests, agriculture and native wildlife.

The ants - referred to as crazy because of their erratic behaviour when disturbed - are thought to have been introduced to Christmas Island about 70 years ago.

Dr O'Dowd, of Monash University, and his colleagues first noticed the invaders' numbers were increasing dramatically in 1997. When they disturbed the crabs' burrows, ants came pouring out. "There were lots of dead crabs inside," Dr O'Dowd said.

The ants used the crabs' homes to build supercolonies that could expand by up to three metres a day, eventually taking over about a quarter of the rainforest and killing 10 to 15 million crabs.

For the study, published in the journal Ecology Letters this month, the team compared infested and unifested areas.

They found that the extermination of the crabs, which had fed on the forest floor, led to a build-up of ground litter and a change in the number and kind of seedlings, which in turn affected the birds living there.

The ants had also swarmed up the trees, where they eat honeydew secreted by scale insects.

In return, they protected the insects from predators so their numbers swelled. This led to an increase in sooty moulds that live on the honeydew. As the mould spread, its dark colour blocked photosynthesis by the canopy trees, causing dieback and death.

An aerial bombardment with poisonous bait late last year, overseen by Parks Australia and Monash University, wiped out 99 per cent of the ants.

[laurenz]

it is interesting to see how even the tiniest "blind passengers" can wreak havc when brought to another eco-system.
Presumably, the price we have to pay for human mobility...
Still, it's a pity that the consequences of our behaviour could only be corrected by poison bait.

Australia has been the victim of such "invasions" before - we introduced quite a few foreign species there: the rabbit, the hare, the feral cat, rats, the fox, the cane toad and even camels.

Laurenz