Invasion of the toads

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Toxic and invasive, the Asian toad is a recent arrival to Madagascar. It poses a grave threat to the country’s unique native species.
Credit: James Reardon

In early 2014, biologist Jonathan Kolby was working with a group of amphibian researchers in Madagascar when they received a surprising email from a man living outside of Toamasina, the country’s major port city. He’d attached a picture of a brown toad never before seen on the tropical island nation known for its rich biodiversity. Intrigued, the researchers found the man’s house, just next to a nickel refinery, but they didn’t expect to find the toad. The man assured them that wouldn’t be a problem. “Wait 10 minutes,” he said.

Shortly afterward, as dusk fell, they stepped outside and immediately saw half a dozen Asian toads. “Big, fat breeding-size adults,” recalls Kolby, a PhD candidate who studies amphibian diseases at Queensland’s James Cook University. “We were like, ‘Shit, this is bad’.”

Two years on, that’s still the scientific consensus. This bumpy, toxic toad from Southeast Asia, Duttaphrynus melanostictus, is disrupting Madagascar’s fragile ecosystems, imperilling its unique wildlife and threatening its people. The poison in the toad’s skin can kill animals and even children. If it continues to spread, the toad could spell serious trouble for some of the island’s most iconic species of lemur and fossa (the lemur’s predator, which looks like a small puma), animals already threatened by habitat loss.

Now a group of herpetologists and invasive species experts is pushing to eradicate the rapidly reproducing toads before it’s too late. With some four million toads to kill, it would be one of the largest attempts ever made at stomping out an invasive amphibian. The campaign would likely cost anywhere from US$2 million to US$10 million, money the scientists don’t have.

They’ve asked for help from a mining company whose shipping containers may have provided the pathway for the invasion, but the company – while generally co-operative, and helpful in first identifying the toad as a problem – has declined so far, citing a lack of hard evidence that it was at fault and choosing to defer to the government on a direction forward.

Even if the scientists raise the funds, there’s no guarantee the eradication campaign will work. But experts say failing to take action would have even greater costs.

“I cannot imagine how decision-makers in Madagascar could sleep at night if they simply said, ‘Sorry, it’s going to cost too much to deal with this. The cat’s out of the bag already’,” says Pete Lowry, a biologist at the Missouri Botanical Garden and a board member of Madagascar Fauna and Flora Group, which is helping to co-ordinate the eradication effort.

“The potential consequences are devastating,” he says. “Madagascar is one of the hottest biodiversity hot-spots.” About 70% of the island’s roughly 250,000 plant and animal species live nowhere else on Earth.

Earlier this year, the group released a feasibility report that makes the stakes clear. “Eradication is the only option that has a definitive end point,” the report explains. “All other responses would need to be carried out in perpetuity.”

The threat has special resonance because of what happened 9,000 km away in Australia, starting in 1935 when 100 cane toads were imported from Hawaii by sugar farmers hoping to control beetles that were destroying their crops. The toads ran amok, spreading across much of the continent and causing severe reductions in the populations of some predators who died after eating them.

In many habitats, cane toads have contributed to the decline of lizards such as the goanna, and marsupials such as the quoll, which are top-of-the-food-chain predators that keep ecosystems functioning. Eight decades on, Australians are still working to contain the toads.

Scientists are developing fences that keep the toads away from breeding grounds and chemicals that trap the tadpoles. Backpackers touring Australia can even earn visa points helping to fight the toads’ spread.

The Asian toads could turn out to be just as destructive as the cane toads have been in Australia, according to James Reardon, a zoologist with New Zealand’s Department of Conservation and co-author of the report. “I absolutely know that if we could go back to a time when cane toads were limited to a small area in Australia – as Asian toads currently are in Madagascar – that we would throw everything at an eradication attempt,” he says.

In Madagascar, the matter is urgent because scientists expect the toads to spread quickly. Currently they occupy about 120 km2 near the Pangalanes Canal, a perfect conduit for amphibians that runs down the tropical east coast of the island.

Lemur expert Patricia Wright of Stony Brook University worries the toads will travel down the canal to the city of Mananjary and then move inland to Ranomafana National Park, a biodiversity haven she has worked to protect for more than three decades.

The toads may already have arrived on a narrow strip of water leading into the canal, the scientists worry. Letting the toads reach the main body of the canal is “like building them a highway to the rest of the country”, says Christopher Raxworthy, a herpetologist at the American Museum of Natural History.

Since the island has no other toads, its predators and prey are particularly vulnerable to the unfamiliar invader, the report warns. The tenrec, a hedgehog-like creature found mainly in Madagascar, is one of many animals that could eat the toad and die from the toxins.

The voracious Asian toads are also likely to prey on the hundreds of colourful frogs and other amphibian species on the island – 99% of which are found nowhere else – and they could eat leaf chameleons or hatchlings from any species, says Raxworthy.

The threat is just as real to people. Children in Laos have gotten sick and, in at least one case, died from consuming the Asian toad, and the risk to Malagasy people, less familiar with the toads, may be even greater. The report also says that snakes are dying after eating the toads; a decline in snake populations could cause black rat numbers to surge, and more rats could mean more sanitation issues in a country that already battles the plague.

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Researchers gather intelligence on the age and gender of Asian toads to aid eradication efforts.
Credit: James Reardon

Scientists have three important reasons to hope that an environmentally friendly eradication is possible. First, the infested area contains no rare or native species that could be harmed during the attempted eradication. Second, male toads convene around bodies of water at night, calling females, so there’s a convenient place to capture or kill them. Finally, recent testing reveals that spraying a citric acid solution – with a concentration similar to lemon juice, according to Raxworthy – kills toads through rapid dehydration without doing serious harm to other animals.

As a next step, members of the working group hope to do a “mini-eradication” along the southern edge of the incursion zone, in order to restrict the toad’s expansion into the canal and further refine killing methods. But even this small effort would cost about US$400,000, and the scientists are still looking for the funding.

“We’re essentially operating on a shoestring budget,” Reardon says. “It’s been a sort of ragtag collection of donations from the international conservation community.”

This raises the question: who should pay to handle invasive species such as the Asian toad in Madagascar?

To invoke corporate responsibility, scientists like to refer to the transport of invasive species as “biological pollution”. A seminal 1998 study led by David Wilcove, now an ecologist at Princeton, cites invasive species as the second leading cause of extinction in the US after habitat loss.

James Carlton, a marine biologist at Williams College in Massachusetts, has proposed that a “polluter pays” model be adopted for invasive species control. Petroleum companies have used such a system since the Exxon Valdez disaster: when their tankers take to the water or their pipelines begin pumping crude, they pay a few cents per barrel into a fund for future cleanups. But right now, companies at risk of shipping and transporting invasive species pay no such fee, so there is no fund for control or eradication.

Calling the current system “ecological roulette” because of the lack of regulation, Carlton writes, “Industries that play a fundamental role as vectors transporting non-native species should bear more of the costs of prevention, control, and research.”

In the absence of such a comprehensive system for dealing with invasive species, experts are left to sort out responsibility on a case-by-case basis – a difficult task. Scientists in the working group suggest that nickel and cobalt company Ambatovy may have accidentally transported the toad to Madagascar in a shipping container. The company was bringing equipment and supplies into the incursion zone to construct a large refinery about the same time the working group believes the first toads arrived.

Sherritt International, the Canadian mining corporation that owns 40% of Ambatovy and operates the plant, says that 170,000 containers pass through the port in Toamasina every year, many from Asia, and less than 5% are for its business. “In terms of identifying a specific container or a specific entry point, it’s incredibly difficult to do that,” company spokesman Scott Tabachnick says.

However, Reardon, the New Zealand zoologist, says statistics from the port are not relevant because the toads were not released at the port – in fact, they still haven’t reached it. (But, as with the canal, he worries the toads will soon reach the port, a domestic and international shipping hub, and hop into another container.)

“We’ve got no hard proof, but it’s highly likely the toads are in Madagascar because of Ambatovy’s activities,” Reardon says. The company has a direct rail link from the port to its plant, where containers are unloaded.

But it’s impossible to know for sure how the toads arrived, especially since there are two other importers of goods in the area: Malgapro, a general import/export business based in the core of the incursion zone, and SolCiment Callidu, a company located on the periphery.

“From the point of view of managing Madagascar’s biodiversity and managing this crisis, it doesn’t make any difference who introduced the toad,” says Pete Lowry, who also has an unpaid position on Ambatovy’s scientific advisory panel. “The point is not to look back and say who’s guilty. Time that gets spent doing that is time taken away from acting on this critical issue.”

No matter how the toad problem arose, Lowry hopes Ambatovy will be part of the solution. “There’s a ticking clock,” he says. “Everybody who has something to contribute needs to step up to the plate and get started – now.”

After a December meeting, Lowry’s advisory panel – a group of scientists separate from the one that completed the feasibility report – recommended the company “take the lead” on toad eradication efforts, acknowledged Ambatovy spokesperson Vony Ramahaleo in an email. But the company points out that it already sits on the committee set up to deal with the invasion, along with government ministries and conservation organisations. “As the government of Madagascar has appointed a committee to lead this fight, we cannot substitute for them,” writes Ramahaleo.

Without major donations, eradication efforts are on hold. But local people are still eager to get rid of the toads, which they call radaka boka (“leprous” or “scaly” frogs) or radaka Dynatec (which translates roughly to “frogs from Ambatovy’s refinery”). Mikahely, a side project of the popular Malagasy music group Mika & Davis, recently released a song, Radaka Boka, about the invasion. Even the country’s three telecom companies have teamed up to help; they’ve started a free text message system so people can report toad locations.

Still, Kolby regrets that more has not been done in the two years since he first spotted the toad. “Right now it’s still worth going forward with eradication,” Kolby says. “At some point it will become infeasible. The longer it’s delayed, the less likely it is to succeed. Without a doubt, we’re running out of time.”

Credit: This feature was adapted and reprinted with permission from Ensia magazine. View the original at


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The South American cane toad was a solution that became the problem.
Credit: edelmar / Getty Images

Lesson from Australia: Know your enemy

For 80 years, Australia has waged a war on cane toads. Now it’s winning some minor victories that may help Madagascar defend against its own amphibian invader.

It began innocently enough: In 1935, Australian officials brought in a hundred South American cane toads to control Queensland’s sugar cane beetles. But this “solution” quickly became the problem. The toads multiplied and marched westward to colonise new tropical habitats, covering 45 kilometres per year. By the time officials realised there was a problem, it was too late. Australia had invited in an enemy, and nothing could conquer it: not trapping, poisoning or a burgeoning market for toad leather. Many of Australia’s unique native species suffered, mostly large ones with catholic appetites. The largest and fastest-moving toads broke new territory in the richly biodiverse wetlands of Kakadu National Park. Toads grow disproportionately more poisonous as they get bigger. Predators big enough to eat them, like goannas and quolls, had no chance to get an education. They dined and died.

The good news is that while their numbers plummeted – the goanna population dropped by more than 90%, for example – these species did not go extinct. Following the initial incursion, toads bred and toadlets appeared – distasteful to predators but not deadly. As predators have grown wiser, numbers have started to recover.

That’s just one of the surprises revealed in the Australian invasion. “It underlines the first rule of warfare: know your enemy,” says evolutionary biologist Rick Shine at Sydney University.

Two successful control strategies have emerged from that knowledge.

It turns out that cane toads gravitate to disturbed environments – farmers’ ponds rather than natural waterholes. A female lays a clutch of up to 40,000 eggs, creating an instant crowd. So cane toads are their own biggest competitors. Shine’s lab discovered that tadpoles dine on newly-laid egg sacs. Poisons seep out of the sac, repelling every other type of tadpole, but attracting cane tadpoles who are resistant to its effects.

The discovery is the basis of a safe new eradication strategy. Traps laden with the poison are placed in dams, attracting and snaring tens of thousands of tadpoles. By developing a commercial product readily available in local shops, Shine hopes to see a large impact on toad numbers.

Melbourne University biologist Ben Phillips has made use of the toads’ natural dependence on seasons to plan his strategy. The next area under threat is the Pilbara, an arid region of immense biodiversity on Australia’s northwest fringe. To reach it, the toads must use farmers’ stock dams as their highway, their only chance of survival in the dry season. That’s when Phillips’ campaign to make the dams toad-proof will roll out.

Will any of this war history be useful for fighting Madagascar’s Asian toad invasion?

At last count, there were four million Asian toads spread over 100 square kilometres. Compared to Australia’s 1500 kilometre sprawl, it sounds containable.

But in Madagascar, it’s a different toad and a different ecosystem. What works in one place may not work in another. “You can’t cut and paste”, says Phillips.

One thing the Australian scientists are sure about is that more research must be done, and quickly. They’ve discovered that every generation of invading cane toads gets faster and faster: the individuals at the leading edge of the invasion are the speediest, and they tend to breed with each other.

Madagascar had better get moving. — Elizabeth Finkel

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