Poisonous Cane Toads Threaten to Ravage Australian National Park's Ecosystem

Cane toads, which have become the plague of northern Australia, are now threatening one of the world's last unspoilt wildernesses. After making a first tentative appearance in the Kakadu national park last March, the large, ugly creatures are expected to take hold over the next few months in the favourable conditions of the wet season.

Each female cane toad lays up to 40,000 eggs a month, and half that number can expect to develop into tadpoles within three days. The toads' highly poisonous skin grants them freedom from any natural predators in Australia, and populations have boomed ever since the first creature was introduced from Venezuela in the 1930s.

The amphibians expert Professor Mike Tyler, of Adelaide University, believes that the problem will be particularly acute in Kakadu, where an abundance of fresh water and native wildlife will provide a nursery for burgeoning populations.

"You can now forget about Kakadu," he said.

"Kakadu is lost. They're going to be more prolific here than elsewhere, and they're going to get bigger. It will become the most dominant form of life in a little bit of Australia that we thought was pristine."

Biological intransigence

The toads have breeding populations across 400,000 sq miles of northern Australia, and are moving west and south along river valleys at speeds approaching 60 miles a year.

According to the Australian scientific institute Csiro, populations in the country are ten times denser than those in their native countries, and the toads are believed to number as many as 100m across the continent as a whole.

"Advance parties" have taken lifts on cars and in camping equipment to turn up in the suburbs of Sydney and Perth.

The creatures were introduced to northern Queensland in 1935 in an attempt to control the grubs of the cane beetle, which were infesting sugar cane crops.

In a famous example of biological intransigence, the toads refused to eat the beetle grubs but consumed just about everything else in their path.

Their arrival in Kakadu has sharpened concerns about their spread.

At 8,000 sq miles, the park is nearly half the size of the Netherlands, and it is one of the few areas of Australia which has remained relatively untouched by introduced species. It is home to 340 species of birds and mammals, 55 kinds of freshwater fish, 1,600 kinds of plants, and more than 10,000 insect species.

Dan Baschiera, a former ecotourism operator who has been tracking the spread of the toads across Australia's north, warned that the coming "blanket of amphibia" would devastate native wildlife.

"I have fears that we're going to be looking at probably two to three times the breeding rate we've seen elsewhere in Australia," he said. "My worst fear is that we're going to get such a substantial swarming of the cane toads throughout the region that it's going to kill everything in its path."

When the first cane toads were discovered in Kakadu last year, the Australian government immediately provided a A$1m (£360,000) grant to research gene technology to control the pest, but conservationists warned that the contribution was too little, too late. As yet, scientists have come up with no effective way of limiting the spread of the toads.

The first animals to feel the impact of the toads are expected to be turtles, snakes, goanna sand-monitors, and the quoll, a fox-like marsupial.

Even the feared freshwater crocodile is no match for the toad's poisonous skin. Last year more than a dozen crocodiles were found floating belly-up in the Katherine Gorge to the south of Kakadu after eating the toads.

Vulnerable

Australia's unique ecosystem, isolated from the world when the continent of Pangaea split 200m years ago, it is particularly vulnerable to introduced species.

Rabbits, which at one point numbered 200m in Australia, have been reduced to a tenth of that population after culls and the introduction of myxomatosis.

But few hold out any hope that the explosion in the population of cane toads can be similarly suppressed before they devastate Kakadu.

"They are going to conquer the whole of northern Australia," said the Northern Territory's parks and wildlife director, Bill Freeland. "That is a reality, and there really isn't a practical way of stopping them or doing anything about it."