Weighing in at to up two kilos (4.4 pounds), the unwanted anuran has extended its range to more than a million square kilometers (386,000 square miles) in tropical and sub-tropical Australia, crushing native species in its relentless advance.

A team of University of Sydney toad watchers positioned themselves on the front line of the invasion, 60 kilometers (35 miles) east of the city of Darwin, and for 10 months caught toads, some of which they radiotagged and let loose again.

They were astonished to find that the creatures can hop up to 1.8 kms (1.1 miles) a night during wet weather, a record for any frog or toad.

But even more remarkable was the discovery that the first toads to arrive at the front invariably had longer hind legs than those which arrived later.

by comparison, the toads which are living in the long-established Queensland colonies have much shorter legs.

The case is being seen as a classic example of Darwinian evolution -- animals that are stronger, faster or smarter are able to stake out new territory and defend it against those that are weaker, slower or less astute.

The findings also neatly explain a puzzle surrounding the cane toad.

From the 1940s to 1960s, the critter expanded its range by only 10 kms (six miles) a year. Today, though, it is advancing at the rate of more than 50 kms (30 miles) annually.

The reason: with longer legs, the mutating species is able to travel further, faster.

The authors, led by Richard Shine of the university's School of Biological Sciences, say the cane toad is a chilling lesson for governments to combat invasive species as soon as possible, "before the invader has had time to evolve into a more dangerous adversary."

The paper appears on Thursday in Nature, the weekly science journal.

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