| Native ant may stop toad in its tracks|
|A ferocious native ant may help save wilderness areas in northern Australia after ecologists discovered it is an effective killer of the feral cane toad.|
In a paper published today in Functional Ecology, Professor Rick Shine of the University of Sydney and colleagues reveal that meat ants, which are common across northern Australia, are deadly predators of baby cane toads.
He says the meat ant has huge potential as an environmentally friendly, low-risk solution to the toad plague because it poses no threat to native frog species.
The 1935 introduction of cane toads (Bufo marinus) into North Queensland to control sugar cane beetles has been an ecological disaster for Australia.
Native animals fall prey to its deadly poison and the ecology of World Heritage-listed wilderness areas, such as Kakadu National Park in the Northern Territory, are under threat.
As part of the new study, the team compared cane toads and seven native frog species by examining where they lived, when they were most active and how good the frogs and toads were at avoiding the meat ants.
They also measured maximum hop distance, and in a purpose-built runway compared sprint speed and endurance.
On every comparison, says Shine, the toads were in a more vulnerable position.
The cane toads were not only slower and hopped shorter distances, but they were most active at the same time and place as meat ants - near hot, sun-exposed edges of water bodies.
"All of the sensible frogs run around at night, however for the young cane toads the risk of cannibalism by larger, older toads is so great the metamorphs emerge on the water's edge during the day," he says.
"This means the baby toads are encountering this large and voracious ant."
He says only one native frog species, Opisthodon ornatus is active during the day and it is "paranoid" of meat ants, constantly scanning for them and moving away when they approach.
Shine says, the cane toad's defence is to stand still.
"Toads, like a lot of toxic animals, rely on just freezing and allowing the predator to realise it's poisonous," he says.
"If you are a cane toad in Australia, poison doesn't work on ants and so stopping when someone gets hold of you is a bad idea."
In field trials, study lead author, Georgia Ward-Fear found the meat ants were very effective predators, in some instances killing up to 90% of the baby cane toads near the water's edge.
Shine says the cane toad's "Achilles heel" is the result an "evolutionary trap".
Because the cane toad evolved in South America where large, predatory ants do not exist it has not evolved traits or behaviours to deal with this threat.
Shine and his team believe this trap could be harnessed as a weapon to fight the invasive pest.
Meat-ant numbers could be manipulated to increase mortality rates when baby cane toads are emerging from the water.
But, he says more research is needed on how this might impact on native fauna and whether the numbers of metamorph toads killed would have an impact on overall population.
"The example of the toad itself shows that when you talk about biological controls you've got to tread very carefully."