There's more than one way to kill a cane toad. And in Australia, where they represent a persistent and dangerous invasive species, it's important to have at least one method at the ready. A new study promises that an old method -- currently condemned for supposedly causing pain -- is actually as humane as toad killing can get.
Because of Australia's isolation as a continent, it developed a rich ecosystem unlike any other. But when colonists showed up from Europe, the foreign species they brought with them had no natural predators and ran rampant. Cane toads were actually brought in to control pests -- the cane beetle, which eats sugarcane crops, specifically -- but with an estimated population of over 200 million, it's no longer a welcome guest. Plus the species is dangerous: They secrete a strong poison, so local animal populations have to learn not to eat them or suffer the losses. The poisons they secrete don't kill humans, but they can cause severe pain.
In the study published Tuesday in Biology Open, researchers led by Rick Shine of the University of Sydney's School of Biological Sciences measured the brain activity of cane toads as they were chilled in a refrigerator and then frozen.
"This procedure was a widespread method for humanely killing amphibians and reptiles for many years until about 20 years ago, but animal ethics committees decided it was inhumane because the animals' toes might freeze while their brains were still warm enough to detect pain," Shine said in a statement. "However, our work shows that in cane toads at least, the toad just drifts off into torpor as it cools down, and its brain is no longer functioning by the time its body begins to freeze."
Australia won't be dumping massive piles of cane toads into industrial freezers: When it comes to wide-scale extermination, there are chemicals better suited to the job. But most citizens don't have access to those pesticides, and the current suggestion is that they hit the toads over the head with a hammer.
"But a slight misjudgement may result in severe pain for the toad, and a splash of toxic poison up into the hammer-wielder's eyes," Shine said.
According to the brain activity recorded during his experiments, freezing is a safer way to go: The toads drift off into a hazy sleep long before any of their extremities register pain.
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