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Australia

Poisonous cane toads mating with mangoes, snakes and killing crocodiles: Australia battling an infestation of ‘epic proportions’

  • The amphibian, native to the US and Americas, was introduced to control a beetle outbreak, but the experiment failed spectacularly
  • The animal has spread almost uncontrollably, and now covers 1.2 million sq km of the continent
PUBLISHED : Wednesday, 02 January, 2019, 6:34pm
UPDATED : Thursday, 03 January, 2019, 5:39pm

A group of cane toads made headlines when they were caught hitchhiking on a python to escape an overflowing dam in Kununurra, Australia. But experts say these venomous amphibians were actually trying to mate with the reptile, and are a serious threat to Australia’s biodiversity. The toad has taken over more than 1.2 million sq km of the continent, devastating native species as they rapidly spread across the country.

How the cane toad invasion began?

Cane toads, which are native to the southern US, Central America and South America, were introduced into Australia in 1935 to control beetle attacks on Queensland’s sugar cane plantations. Instead of killing the pests, the 102 cane toads – 51 males and 51 females – brought from Hawaii reproduced prolifically and became pests themselves.

“The experiment failed spectacularly,” said Robert Capon, professorial research fellow at the University of Queensland’s Institute for Molecular Bioscience. “Cane toads showed no interest in the beetles whatsoever, and instead launched a global invasion of epic proportion.”

Adrian Bradley, honorary senior lecturer at the University of Queensland, said cane toads have become a successful species because they arrived in Australia without most of their native parasites, which help control their numbers.

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How poisonous are cane toads?

Cane toads are highly poisonous at all stages of their life cycle: as eggs, tadpoles and adults. And they become more dangerous as they get older.

The toxin in their parotoid glands – located on the side of their heads – can kill large reptiles in around 90 seconds, according to Peter White, professor in microbiology and molecular biology at the University of New South Wales.

Native predators, such as the northern quoll, goannas and snakes, have evolved to eat non-poisonous native frogs but are fatally poisoned when they try to eat cane toads. The deadly poison has even killed freshwater crocodiles.

Cane toads’ poison can be fatal to humans if the toxin enters the body through the mouth or the eyes, for example.

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How have they spread so quickly?

A healthy female toad can lay 30,000 eggs that hatch into tadpoles.

“Cane toads can be so keen to grab on to a female of their own species to mate, that they grab on to a wide variety of other things, such as frogs of different species or human boots [if someone happens to walk through a pond with frogs breeding],” said Jodi Rowley, senior lecturer in biological sciences at the University of New South Wales.

“I’ve seen an excited male cane toad in amplexus [the mating position] trying to mate with a rotting mango, and I’ve seen photos of toads trying to mate with empty beer cans and cameras!

“They usually realise their mistake and release after a short time. It may seem strange, but it’s a strategy to avoid missing any female cane toads coming to a breeding site to breed. If the toad is too slow, another male might hop on and get to fertilise her eggs! It’s an extremely competitive environment!”

What’s being done to stop them?

For many years, Toad Busting – hand capture of adults – has been the only option for reducing cane toad numbers.

The problem has become so widespread that some Australians have even resorted to beating the notorious pests with golf clubs and cricket bats.

Recently, a taste aversion conservation strategy programme was launched by Richard Shine of the University of Sydney. The strategy trains native animals not to eat the toads by feeding them sausages that cause vomiting and an aversion to both the taste and smell of the toad.

New research developed by the University of Sydney, in collaboration with the University of Queensland, shows the cane toad’s poison can be used as a weapon against itself – the toxin can be used as “bait” to catch toad tadpoles, which are highly attracted to the poison.