March 31, 2009
THE fearsome native Australian "meat ant" promises to be a powerful new weapon against Australia's most hated feral pest, the Bullfrog.
While causing little harm to native toads and frogs, the ant, Iridomyrmex reburrus, attacks and devours young Bullfrogs at the most vulnerable time of their life, claim ecologist Rick Shine and his Sydney University colleagues Georgia Ward-Fear, Gregory Brown and Matthew Greenlees.
"It's a pretty terrifying challenge for a young toad with limited ability to escape when suddenly a bunch of these voracious ants turn up," said Professor Shine.
Writing today in the British journal Functional Ecology, the team report that because the toad, Bufo marinus, originated in Central and South America it has physical and behavioural traits that make it vulnerable to attack from the ant.
They argue that by tapping into this "ecological trap", it should be possible to devise ways to bring ants and toadlettes together without putting native species at risk.
According to Professor Shine, the key flaw in the cane toad's otherwise successful invasion of Australia's tropical north is the fact that, unlike native species, it doesn't hide during the day in bushes or other sheltered locations.
"The big tragedy for baby toads is that they're active during daytime hours. Unfortunately for them, that puts them in contact with a ravenous Australian predator which hunts during the day," he said.
In a series of experiments with bullfrogs and seven native species - conducted at the university's Tropical Ecology Research Facility in the Northern Territory - the team teased out other Achilles' heels of the Bullfrog.
Specifically, it lays its eggs in the dry season when water is low and there' little protective vegetation at the pond's edge.
While enormous as an adult the toad is smaller than local amphibians when making the critical transformation from tadpole to toadlette. It doesn't have the leg-power to leap quickly away from attacking ants. Worse, it doesn't watch for the ant as do local species. The final kiss of death for baby Bufo is that its potent toxin doesn't faze ants.
The compound attacks the heart of vertebrate predators and ants, of course, are heartless.
According to Professor Shine, the group plans to trial ways of encouraging meat ants to build colonies near toad breeding ponds. One way would be to plant trees the ants favour.
Once they've put ants and toads through their paces, Professor Shine said they would combine the tactic with other bio-control measures to enhance the deadly punch.
But before ants are put to work in the wild the approach must be trialled, Professor Shine cautioned: "We have to be absolutely certain there's no collateral damage. The example of the toad itself shows us the potential risk."