Invasion front: In 2007, biologists found the cane toad's range had expanded to 1.2 million square kilometres in a swathe across Queensland and the Northern Territory.
Credit: iStockphoto
PARIS: They've tried gassing it, freezing it, running over it in cars, whacking it with golf clubs and turning it into compost. But the cane toad, an insidious invasive species introduced to Australia nearly three-quarters of a century ago, has multiplied regardless.
Now, though, a new study suggests that Bufo marinus has a weak spot: it is vulnerable to a native Australian ant.
The cane toad, indigenous to Central and Latin America, was brought to Australia in 1935 to help control beetles that threatened sugar-cane crops.
Fiercely aggressive ant
The critter has now spread across much of northern Australia, killing native carnivores – including crocodiles, snakes and lizards – that cannot tolerate its toxins, and devastating native frogs and toads through habitat loss.
The Australian authorities have tried desperately to stop the invasion, including a "Toad Day Out" in the state of Queensland, which encourages people to hunt down the hated anuran.
In the study published this week in the journal Functional Ecology, a team led by the University of Sydney's Rick Shine report that the pest is vulnerable to the meat ant (Iridomyrmex purpureus) – a fiercely aggressive, omnivorous species found all over Australia.
In a special laboratory, the biologists compared use of habitat and behaviours between cane toads and seven native Australian frogs.
Cane toads are active during the day – when the meat ants themselves are busy – and live in open micro-habitats. Aussie frogs, though, are nocturnal and tend to hole up safely in vegetation during the day, when meat ants are on the prowl.
Evolutionary trap
In addition, the scientists found, the Australian frogs are warier of the meat ants than the imported intruder and also quicker and nimbler at avoiding them compared to the cane toad, whose hops are shorter and slower due to shorter shin bones.
Ants' nests could thus be used as a defensive tool against toad expansion, goes the thinking.
"The spread of cane toads through tropical Australia has created major ecological problems," Shine said. "The ideal way to control toad numbers would be to find a predator that kills and eats toads but leaves native frogs alone."
