Cane toads that were buried alive in WA's north are essentially "baked to death" in the hot conditions, which according to zoologist Peter Mawson, is not a humane way of killing the pest.
The invasion of poisonous amphibians into Western Australia has reached Lake Argyle in Kununurra, on the Northern Territory boarder, prompting the Department of Environment and Conservation to conduct trials into the humane killing of the toads.
The DEC and the Kimberley Toad Busters, which works to eradicate the toxic animals from the area, sealed 376 cane toads in bags to gauge how long they had to be exposed to carbon dioxide before they died.
Dr Mawson said groups like the Toad Busters often dealt with thousands of amphibians each night and prior to the study, some had been inadvertently buried alive.
"You have a situation where they were burying between 1000 and 10,000 toads each day in soil that could reach temperatures of 40 degrees," Dr Mawson said.
"If only one or two per cent of those weren't dead when they were buried, that's 100 that slowly bake and have a horrible death, or they dig themselves out and carry on doing what they were doing."
The trials revealed the pests could survive for three hours when exposed to carbon dioxide because of their ability to hold their breath for up to an hour and were able to distribute chemicals and gasses like CO2 around their body so it did not poison them, Dr Mawson said.
"In our first trial we found that after carbon dioxide gas was pumped into a properly sealed bag containing cane toads, all of the animals were dead within four hours," he said.
"During the second trial, it was determined that up to 20 cane toads per bag could be euthanized by exposure to carbon dioxide gas."
He said once the "very tough animals" were bagged and exposed to the gas they became placid.
"They just go very quiet, they draw their legs up close to them and then the next thought they have is in heaven - that's if cane toads go to heaven," he said.
"The only real change is the skin on the belly goes a lovely pink colour."
Last month a male cane toad was found in a Bayswater front yard, sparking an investigation to find out how it arrived.
Dr Mawson said the amphibian had most likely been in the garden for a long time because it didn't show any damage from a long trip.
"But there are people planting palms in their gardens in the area and toads have been buried in potting material and transported that way in the past," he said.
"The particular garden he was found in was lush and had ground lighting, which is great for them because they attract insects so the toads tend to just park themselves under them and have a feast."
Under the Animal Welfare Act all animals, including pests like cane toads, must be killed in a humane manner.