Like any good biologist, Rick Shine of Australia never ventures into the field without some essential tools: a notebook, a camera, containers for samples — and cat food. It’s not an odd choice of snack on Shine’s part, nor is it bait for some elusive wild cat with a domestic palate. Cat food is actually the latest weapon in the battle against Australia’s most infamous pest: the cane toad.
Spread a little Whiskas “Ocean Platter” cat food around ponds where invasive cane toads breed and you’ll soon attract omnivorous meat ants, who relish baby toad flesh. The ants attack the young toads just as they’ve left the safety of their ponds for land, still undergoing metamorphosis towards true adulthood. Shine, a University of Sydney evolutionary biologist, described the new strategy in a study published this month in the British Ecological Society’s Journal of Applied Ecology.
First introduced from Hawaii to Australia in 1935 to help control beetles that were threatening Australia’s sugar cane crops, cane toads have grown over two million strong in only 75 years. In the absence of any natural predators or parasites, poisonous cane toads have spread across the Australian continent at an alarming rate, killing many native frog-eating predators who mistake the toads for a non-toxic frog. Such predators include lizards, crocodiles, marsupials, and dingoes.
“We’ve seen 70 to 90 percent of some of these large predators die at the invasion front as the toads come through,” Shine said. “Any predators in Australia have no exposure to the toads’ poisons.”
Cane toads also compete with native species for food and may spread diseases to Australian amphibians, not to mention the occasional poisoning of both pets and humans who handle the toads too closely. Australians have tried everything to curb the toads’ rampant expansion, from beating them with golf clubs and cricket bats, to more humane methods like sticking them in freezers or suffocating them with carbon dioxide.
Shine’s new approach has proven remarkably effective. After sprinkling cat food around the ponds, Shine observed swarms of meat ants attack 84 percent of the emerging toads. 50 percent of those attacks were immediately fatal and, of the toads that escaped, 88 percent died from their injuries within 24 hours.
The aggressive meat ants and young toads are around the same size (less than half an inch) and the toads tend to reflexively freeze when attacked, permitting the ants an easy picnic. Unlike most of Australia’s native predators, meat ants are immune to cane toad poison and regularly prey on the emerging toads. Cat food simply encourages them, increasing toad mortality rates.
The fact that meat ants are native to Australia is especially appealing to many biologists concerned about further tampering with the continent’s ecology.
“That’s brilliant,” said James Danoff-Burg, an invasive species expert at Columbia University. “Instead of introducing another species into an ecosystem, take advantage of local species.”
But Shine is still wary. He doesn’t think his new technique — or any other — will truly solve the cane toad problem.
“I’m encouraged that our work is showing a range of vulnerabilities of toads that potentially we can use to control them,” Shine said. “But we are very keen not to repeat the mistake that people made when they brought cane toads to Australia. We can make life for cane toads more difficult in Australia, although we will never get rid of them.”
For a fascinating exploration of the relationship between cane toads and Australians, you’ve got to check out the popular documentary Cane Toads: An Unnatural History and its sequel, Cane Toads: The Conquest, which just premiered at the 2010 Sundance Film Festival to positive reviews. Most Australians despise the unstoppable hoppers, but—as the films show—others are enchanted by them.
As Shine says, “Toads are a desperately impressive animal.”