Dead Cane Toads Are Deadly

The deadly-when-eaten invasive amphibians that have been plaguing Australian wildlife for years continue to poison even after they’re dead.

Jul 5, 2011
Edyta Zielinska

Cane toads collected in AustraliaBRENDAN BORRELL

The classic example of an introduced-species-gone-awry gets even worse. Not only do living cane toads regularly kill many of Australia’s endemic predators that hunt and eat the hopping meals, dead toads—common roadkill along Australia’s highways—are threatening local aquatic fauna.

Cane toads have blighted Australia every since the animals were introduced to the continent in order to control beetles that were damaging sugar cane crops.  In addition to being largely unsuccessful in controlling the beetle population, the toads bred prolifically, decimating natural predators such as snakes and lizard, which were poisoned by toxins produced by the toad called bufatoxins.

Researchers had assumed that dead toads, which line highways and find their way into streams and ponds, wouldn't pose a threat to aquatic organisms because bufatoxins are not water-soluble. But according to a new study published in Biological Invasions, even dead toads can kill. Researchers collected dead and dried toads from roadsides and soaked the amphibians in water, together with several native aquatic organisms such as fish and tadpoles. Most of animals died within a day, suggesting that the toads produce other deadly toxins that have yet to be identified.

"Previously you thought, 'Well, okay, a dead cane toad is an ex-toad. It's no longer any problem,' " Michael Tyler, a herpetologist at the University of Adelaide, North Terrace, in Australia told ScienceNOW. "What these guys have done is to demonstrate that it remains a very serious conservation problem."

(Read The Scientist's feature article on the controversial genetically-engineered virus being designed to Stop the Cane Toad.)