Researchers with the University of Sydney found that a few tablespoons of cat food left next to ponds in the Northern Territory attracts fierce Australian meat ants, which then attack baby cane toads as they emerge from the water. The results of the study were published in the British Ecological Society's Journal of Applied Ecology this week.
It is the latest weapon in Australia's seemingly endless battle against the cane toad, which was introduced from Hawaii in 1935 in an unsuccessful attempt to control beetles on sugarcane plantations. The toads bred rapidly, and their millions-strong population now threatens many species across Australia.
Early cane toad killing methods included whacking the creatures with golf clubs or cricket bats. In recent years, most groups dedicated to fighting the pests have turned to freezing or gassing them with carbon dioxide. Still, the toads' population continues to explode.
Cane toads emit a poison that attacks the heart of would-be predators. But the University of Sydney researchers found that meat ants are impervious to the toads' poison, said Rick Shine, a professor of evolutionary biology at the University of Sydney who supervised the research.
"A single toad can have 30,000 eggs in a clutch, so there's a heck of a lot of tadpoles turning into toads along the edge of a billabong," he said. "You can literally have tens of thousands of toads emerging at pretty much the same time. They are vulnerable to meat ants if the colony discovers there is a source of free food."
Between July and September 2008, researchers studied tens of thousands of cane toads emerging from cat food-lined ponds and found that 98 percent of them were attacked by meat ants within two minutes. Of the toads that escaped, 80 percent died within a day from ant-inflicted injuries.
The baby toads are less than half an inch (1 centimeter) in size, about the same as a meat ant. The aggressive ants have strong jaws and can kill even larger animals by sheer numbers.
"It's a pretty unequal fight," Shine said. "The toads have this terribly stupid response to attack
-- which is just to freeze and do nothing."
Not all think the study is valuable. Graeme Sawyer, an official with Frogwatch, an environmental group dedicated to wiping out the toxic amphibian, said the cat food technique just isn't powerful enough.
"The impact of meat ants on cane toads can be significant with a small number of cane toads, but when you get areas where there are large number of cane toads it doesn't seem to make any difference at all," he said.
Australia's Royal Society for the Prevention of Cruelty to Animals said encouraging ants to attack cane toads is inhumane.
"RSPCA Australia recognizes that cane toads must be controlled, but urges researchers to concentrate on identifying effective methods that do not cause unnecessary pain or distress," the group said in an e-mail.
Shine acknowledged the study doesn't have all the answers.
"You'd have to be a desperate optimist to think that we'll ever see the end of cane toads in Australia," he said.