The invasive toads continue their march across Northern Australia: will there ever be better tools to stem the tide?
I’m grossed out as I sneak through the backyard after dark, a torch in one rubber-gloved hand and a plastic bag in the other.
A rustle of dry leaves nearby alerts me to my quarry – Bufo marinus, or Rhinella marina, otherwise known as the common cane toad, one of an estimated two billion warty specimens spread across Queensland, New South Wales, the Northern Territory and Western Australia.
Wincing, I grasp the glowering toad and shove it in the bag, which already contains five of its mates.
Their writhing intensifies as they accommodate the new captive, bulbous eyes and webbed back toes pressing against the plastic.
It’s this, the getting up close and personal with toads, which grosses me out the most, I confess to Emily Vincent, from the Gold Coast-based environmental not-for-profit Watergum.
Vincent is leading the current Great Cane Toad Bust, a one-week go-for-broke citizen science project which aims to hand-collect and euthanise as many of the unwanted amphibians as possible.
“For a lot of people, it can be a tough thing to get over,” she says. “You just have to man up and think about all the positive effects you’re causing – for the environment, for native animals, for pets, for everything.”
I repeat her words like a mantra as I watch the old bar fridge shake and shudder, having tied off the plastic bag and deposited the night’s catch in there to chill.
Refrigerating toads in this way, says Vincent, sends them peacefully into a coma-like state.
After 24 hours, they can be transferred to the freezer, where they will, finally, croak.
This cool-and-freeze method is the most humane way to kill cane toads, she says, and it’s important not to skip the refrigeration step, because stashing toads straight into the freezer causes them immense pain through ice crystals forming in their veins.
“It’s not the toads’ fault they’re here. They didn’t ask to be on this continent and they’re just trying to survive like everything else,” she says.
I decide it’s the wrong moment to tell her that, as a child, I used to watch a friend’s father gleefully dispatch hordes of them by whacking them with the back of a shovel.
Cane toads first came to Australia in 1935 when an entomologist working for Queensland’s Bureau of Sugar Experiment Stations shanghaied 102 of the critters from Hawaii and let them loose in the state’s cane-fields, hoping they would help control pest beetles.
To say this biological control measure was an unmitigated disaster would be an understatement.
Not only did the cane toads fail to control the beetles, but they bred and ate voraciously, out-competing native animals for food and habitat as they spread up to 55 kilometres a year, according to a CSIRO submission to a 2019 federal parliamentary inquiry into the issue.
Their grim march across the country was effectively super-charged by the toxins in their parotoid glands – so potent that they could fatally poison anything which tried to eat them.
Cane toads have thus been found to negatively impact upon populations of frogs, fish, reptiles (including goannas, crocodiles and blue-tongue lizards) and mammals such as quolls.
For example, a 2021 Endangered Species Research paper looking at two populations of endangered northern quoll (Dasyurus hallucatus) in northwestern Australia found that the cane toads’ arrival led to the quolls “becoming undetectable in one gorge and barely detectable in the other”.
Off the back of a pandemic-led boost in pet ownership, toads are also a concern for the nearly 70 per cent of Australian households who own pets, considering that an adult cane toad contains enough toxin to kill an average-sized dog in 15 minutes, according to the RSPCA Queensland.
My own toad-busting efforts were motivated by a desire to protect a new puppy which has demonstrated uncanny skill at sniffing them out, dead or alive.
But as I venture out, night after night, it starts to feel like a Sisyphean task.
Vincent encourages me keep going.
“It’s a common question we get. Is it worth it? Is it worth trying to do anything about cane toads? Have we already lost that battle? And my answer is definitely not,” she says.
It’s a battle waged on many fronts.
The Cane toads on the march report released in the wake of the 2019 parliamentary inquiry remarked upon a range of biological and genetic solutions, such as modification of DNA to produce “daughterless toads” and a genetically modified virus, designed to interfere with cane toad tadpoles morphing into adults.
However, biologist Professor Rick Shine, who won the Prime Minister’s Prize for Science for his work on cane toads in 2016, stated in his submission to the inquiry that some of the risks of these approaches outweighed the benefits.
“Even if the technology were feasible, the dangers of releasing a self-disseminating GMO [genetically modified organism] would be difficult to justify given the minor ecological impact of cane toads in areas where they have already been present for several years,” he wrote.
“Not only is there a risk of transfer to other amphibian species, but also the risk that any genetic manipulation would find its way to the native range of the cane toad (and related toad taxa) where it could cause catastrophic collapse of an important subset of the world’s amphibians.”
One promising development that has just hit the market is the tadpole trap.
Harnessing research originally conducted by the University of Queensland and University of Sydney and commercialised by Watergum, the traps use lures made from cane toad pheromones, which are harvested from their parotoid glands.
(Just in case I needed another reason to loathe toads, it turns out that their tadpoles are cannibalistic, and can’t resist the lures because they smell exactly like cane toad spawn.)
Watergum has set up several fridge and freezer community drop-off points so toad busters can keep the organisation well-stocked with fresh toads.
The traps went on sale on the Watergum website today.
In another encouraging sign, Australia’s native animals are learning to safely consume cane toads, demonstrating considerable ingenuity in their methods.
For instance, native water rats extract toads’ hearts and livers with near surgical precision, freshwater crocodiles have changed their foraging strategies and crows and magpies flip the beasts onto their backs so as dig into their soft underbellies with their beaks.
“But my favourite is the ibis, the absolute bottom of the bird world in lots of people’s opinions, but they have the best method,” says Vincent.
“They pick up the toads and fling them around, getting them really stressed and causing them to excrete the toxin from their parotoid glands.
“Then they just take them down to the creek, wash all the toxin off, and swallow the toad whole.”
Toad busting, she says, helps reduce toad numbers, giving more native animals a chance to learn how to combat the threat.
Despite the unpleasant nature of the activity, people have also forged friendships and strengthened community and neighbourhood ties through toad busting.
“Toad busting can be something you do in your neighbourhood once a month, then after they’re all dealt with, and everyone’s washed their hands, you can have a big barbecue or a bonfire and get to know your neighbours,” Vincent says.
“You’re joining together to do important work that’s maybe a little bit hard, but it’s good fun.
“You can have competitions who can collect the most, and you’re all working together to make your neighbourhood a better environment.”
Vincent anticipates that the results of this year’s Great Cane Toad Bust will exceed last year’s event, which took 50,726 toads out of commission.
The Great Cane Toad Bust concludes on 29 January 2023.
Originally published by Cosmos as Getting a jump on cane toads
Denise Cullen is a Brisbane-based freelance writer who contributes to a range of local and international publications, including The Australian, The Guardian Australia and Narratively. She is also a registered psychologist.