Sydney  - Australians have tried all sorts of ways to stop the continent's coastal fringe being colonized by cane toads. There's cane toad golf, there are cane toad fences and even cane toad bounties.

But the South American imports, introduced into north Queensland in 1935 to control beetles infesting sugar cane fields, seem unstoppable.

They have hopped into the tropical north and are working their way west in their millions.

Cane toads are a particular pest because they ooze a poison from their necks that can kill whatever eats them. They can grow to over a kilogramme and lay 35,000 eggs at a time.

However Rick Shine, a Sydney University biologist, has found a chink in their formidable armor.

As they've only been in Australia for 80 years, cane toads don't fear a local species called the meat ant as the young of indigenous toads and frogs do. They stand and fight - and they die.

"The cane toad, rather foolishly, tends to just sit there and let itself be ripped to shreds and the meat ants then carry bits of the toad back to their colony," Professor Stine said.

The ants don't die because the venom in the toads is constituted to bring on a heart attack - and ants don't have hearts. Meat ants don't take on adults because adult cane toads are nocturnal and they are not. But cane toad babies emerge from the water and spend their days in the sun, where they are easy prey for meat ants.

What's next for Shine is finding a way of bumping up the number of meat ant colonies in places where there are cane toad nurseries.

"It looks encouraging," Stine said. "Increasing meat ant densities probably wouldn't have too much effect on anything other than the survival rate of cane toads." (dpa)