Backstory: Busting cane toads Down Under

Graeme Sawyer hardly looks like the manager of a multi-media company as he sloshes through a flooded mangrove forest in khaki shirt and shorts on a recent dark evening. The outfit may be vintage Crocodile Hunter, but unlike the late Steve Irwin, Mr. Sawyer has murderous intentions toward the animals he's stalking.

Sawyer is a top general in the defense against a literal amphibious assault – the invasion of the cane toad. The poisonous, warty enemy is legion; the defenders are desperate, resorting to traps, sniffer dogs, and sometimes taking up cricket bats and even hemorrhoid cream to do in the enemy. On this particular evening the strategy is to take as many toads prisoner – for later disposal – as possible.

"We won't be able to wipe them out, but by killing as many as we can, we can minimize their impact," he says, wiping away the sweat and warm rain streaking down his face on this oppressively humid night. "If you just let them breed up, then there'll be absolute devastation."

Sawyer is a founder of FrogWatch, the conservation group that has led the fight in northern Australia against the toxic invaders introduced in Queensland in 1935 to eat a beetle that was damaging the state's sugar-cane plantations.

The experiment was a disastrous failure – the cane toads (native to South America) ignored the beetles but began chomping their way through plenty of other wildlife, from frogs and tadpoles to small lizards. Worse, the poison glands on their backs made them deadly to the crocodiles, mammals, snakes, and birds that tried to eat them.

The toads adapted superbly to the heat and humidity of tropical Queensland, and within decades began pushing south into New South Wales and west into the vastness of the Northern Territory. A couple of years ago they overran Kakadu National Park – made world famous by the Crocodile Dundee movies – and now they're on the doorstep of Darwin, capital of the Northern Territory.

While the task of capturing and killing toads on the ground is left to unpaid volunteers, the federal government in Canberra spends a modest $740,000 a year on cane toad control research, largely through its scientific agency, the Commonwealth Scientific and Industrial Research Organisation. CSIRO scientists are trying to find pathogens and other deadly infectious agents that could be used to wipe out the pests.

Sawyer leads a grass-roots campaign that is trying to prevent toad numbers from building to the point that they'll wreak havoc on the city's wildlife and domestic pets (a mouthful of toad can be fatal to a dog or cat).

Sawyer had a broad interest in the environment when FrogWatch was founded in 1991, he says. "We were looking at frog populations and distributions. We found a new species – a whole bunch of stuff like that."

But gradually he turned his attention to the impending threat posed by the toads as they hopped and croaked their way in their millions across Australia's tropical north. "The closer they got to Darwin the more political and community concern there was," he says.

He started organizing toad "musters" – a word reflecting Northern Territory's status as cattle country. But instead of the motorbikes and helicopters used to herd bovines, toads have to be rounded up the hard way – one by one, by as many volunteers as can be persuaded to give up their evenings to stem the amphibian invasion.

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On tonight's muster, about 30 locals – adults and children – have gathered at the Casuarina Coastal Reserve, a strip of bushland on Darwin's fringe, armed with powerful flashlights and clear plastic sacks.

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