LESSON FROM AUSTRALIA: KNOW YOUR ENEMY

FOR 80 YEARS, Australia has waged a war on cane toads. Now it’s winning some minor victories that may help Madagascar defend against its own amphibian invader.

It began innocently enough: In 1935, Australian officials brought in a hundred South American cane toads to control Queensland’s sugar cane beetles. But this “solution” quickly became the problem. The toads multiplied and marched westward to colonize new tropical habitats, covering 45 kilometres per year. By the time officials realized there was a problem, it was too late. Australia had invited in an enemy, and nothing could conquer it: not trapping, poisoning or a burgeoning market for toad leather. Many of Australia’s unique native species suffered, mostly large ones with catholic appetites. The largest and fastest-moving toads broke new territory in the richly biodiverse wetlands of Kakadu National Park. Toads grow disproportionately more poisonous as they get bigger. Predators big enough to eat them, like goannas and quolls, had no chance to get an education. They dined and died.

The good news is that while their numbers plummeted -- the goanna population dropped by more than 90%, for example -- these species did not go extinct. Following the initial incursion, toads bred and toadlets appeared – distasteful to predators but not deadly. As predators have grown wiser, numbers have started to recover.

That’s just one of the surprises revealed in the Australian invasion. “It underlines the first rule of warfare: know your enemy”, says evolutionary biologist Rick Shine at Sydney University.

Two successful control strategies have emerged from that knowledge.

It turns out that cane toads gravitate to disturbed environments – farmers’ ponds rather than natural waterholes. A female lays a clutch of up to 40,000 eggs, creating an instant crowd. So cane toads are their own biggest competitors. Shine’s lab discovered that tadpoles dine on newlylaid egg sacs. Poisons seep out of the sac, repelling every other type of tadpole, but attracting cane tadpoles who are resistant to its effects.

The discovery is the basis of a safe new eradication strategy. Traps laden with the poison are placed in dams, attracting and snaring tens of thousands of tadpoles. By developing a commercial product readily available in local shops, Shine hopes to see a large impact on toad numbers.

Melbourne University biologist Ben Phillips has made use of the toads’ natural dependence on seasons to plan his strategy. The next area under threat is the Pilbara, an arid region of immense biodiversity on Australia’s northwest fringe. To reach it, the toads must use farmers’ stock dams as their highway, their only chance of survival in the dry season. That’s when Phillips’ campaign to make the dams toad-proof will roll out.

Will any of this war history be useful for fighting Madagascar’s Asian toad invasion?

At last count, there were four million Asian toads spread over 100 square kilometres. Compared to Australia’s 1500 kilometre sprawl, it sounds containable.

But in Madagascar, it’s a different toad and a different ecosystem. What works in one place may not work in another. “You can’t cut and paste”, says Phillips.

One thing the Australian scientists are sure about is that more research must be done, and quickly. They’ve discovered that every generation of invading cane toads gets faster and faster: the individuals at the leading edge of the invasion are the speediest, and they tend to breed with each other.

Madagascar had better get moving.