After a 69-year migration from tropical Queensland in eastern Australia, an infestation of poisonous cane toads is only a short hop away from crossing the eastern borders of Western Australia state. Dire predictions of an environmental holocaust for native wildlife have been uttered as barriers have been thrown up on outback desert roads and remote beaches and waterways in northeast Australia.                                                                      The giant leathery toads (bufo marinus), which can weigh up to 3 kg, were imported from Hawaii and released in Queensland in 1935 in a bid to tackle sugar cane beetles that were destroying about 12 percent of the crops. Unfortunately, the beetles could fly and the toads couldn't, so the former still munch away at the cane plantations, and the latter set forth, at first slowly but in recent years at an alarming and accelerating rate, to multiply in almost every conceivable habitat they could find.    Australia got an idea of the ecological impact the toads could wreck three years ago, when they swept through the World Heritage listed Kakadu Wilderness area on the eastern side of the top of the Northern Territory, almost wiping out quolls [native marsupial predators], as well as snakes, birds and even some salt water crocodiles.       The territorial quolls attacked and ate the toads, which are poisonous. The venom, in glands behind each ear, is sufficiently potent to have killed large crocodiles the same way. As to snakes and birds, the toads either stalk them or sit still looking like a lump of dung before jumping on and eating them. They have also been seen to squirt the venom over their victims from up to a meter away. Although thought to pose little risk to humans, fatalities have been recorded in remote communities where food became contaminated with their poisonous eggs.    The fear is that the more expansive water courses in the north of Western Australia state will prove to be the most favorable habitats yet reached by the toads, where they could wipe out the native goannas, a large meaty lizard that is a staple part of the traditional diet of Aboriginal groups. In the short term, plans are in hand to establish a joint task force to head off any potential incursion by strengthening border patrols and pinpointing areas where floodwaters could carry the toad spawn, which can be attacked with chemicals.    But these measures will only slow down the cane toads until science can come up with a better answer. Currently, the Commonwealth Scientific and Industrial Research Organization says it is about 10 years away from perfecting its preferred answer, a genetic virus that will kill cane tadpoles before they turn into toads.    However, not all scientists believe the march of the cane toads will permanently damage native species. Some argue that they will rebound or adapt just as they did to the arrival of the dingo from China 4,000 years ago. Professor Rick Shine, an evolutionary biologist at the University of Sydney, sees the toads' passage across Australia as “a massive experiment in natural selection.”     Both Shine and government biologist Bill Freeland have pointed to a “learned response” to the toads by some native birds, which in the space of a few years have started to turn them on their backs before eating them, avoiding the poison glands. But no one can say for sure what the long-term environmental impact of the toads will be.