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In 1935, agricultural scientists from the Bureau of Sugar Experiment Station near Cairns committed one of the great blunders of biological control history. They brought 102 cane toads from their adopted island of Hawaii to Cairns, and released their progeny.

Ignoring the beetles they were meant to eat, these warty South American interlopers have spread across more than one million square kilometers of tropical real estate, leaving a trail of environmental destruction in their wake.

The southern front is moving only slowly through northeastern New South Wales, but the western front accelerated as it moved through the Northern Territory. With the first wet-season rains of 2008, Western Australia will join the list of Australian states that are reluctant hosts to this most unwelcome invader.

Unstoppable?

So, are the toads unstoppable? Ecologically-based research has given us a new arsenal of weapons, such as toad-specific parasites and pheromones, providing a glimmer of hope for toad control.

The toad's high public profile and its predicted impact on biodiversity spawned millions of dollars in research funding, and enthusiastic community 'toad-busting', yet failed to slow the toads' invasion.

CSIRO was the primary recipient of funding, and spent several years researching toad biology and pathogens in the animal's native range in Venezuela, and several more years trying to construct a genetically-modified virally-vectored toad-killer.

The work hit technical snags and looks unlikely to continue – perhaps fortunately. Many have pointed to the risks of ecological catastrophe if a genetically-engineered toad-killing virus escaped Australian shores to massacre toads in their native range.

Community attempts at toad control have been equally frustrating – despite massive effort, the toad front has continued to sweep westwards. A single female cane toad can produce up to 30,000 eggs in a single clutch, so the mathematics of population reduction are formidable.

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