New report says there is a ‘diminishing window of opportunity’ to completely eradicate the Asian toad, which poses a threat to biodiversity, human health and the economy

Madagascar must wipe out an invasive, toxic toad immediately to save the country’s unique wildlife from disaster, scientists have warned.

A report published on Wednesday says that the Asian toad is spreading unchecked through the eastern part of the island, and poses a direct threat not only to the country’s biodiversity, but to human health and the economy.



The study, by eradication, invasive species and herpetology experts, examines the feasibility of a widescale eradication programme following successful controlled field tests but warns that there is a “diminishing window of opportunity” to take action.

The Asian toad (Duttaphrynus melanostictus) is thought to have arrived in Madagascar via freight containers travelling from south-east Asia between 2007-10, but it was not properly identified until 2014.



An estimated population of 4 million toads has established a foothold around the port city of Toamasina and is expanding at a rate of 2km a year. If the toads are not eradicated, or at least controlled and contained, they will continue to spread over the majority of Madagascar, the scientists warn.

“The Asian toad can spread across most habitats with no obvious barriers. However, it is currently restricted to about 110 sq km, which gives us hope that we can contain it, but only if we act now,” said James Reardon, an eradication expert with New Zealand’s Department of Conservation, and co-author of the report.

“If the toads become established in the Pangalanes canal system — one of the longest manmade canals in the world — eradication will no longer be an option, and they will likely cause ecological damage similar to that of the cane toad in Australia.”



The toads - also known as the Javanese, black-spectacled or black-spined toad - are long-living, rapid breeders that produce up to 40,000 eggs a year. They secrete a milky toxin that is poisonous to native birds, mammals and snakes that prey on toads.

“Madagascar is a wildlife haven, containing some of the planet’s richest biodiversity, including lemurs,” said Christian Randrianantoandro of Madagasikara Voakajy, and a co-author of the report. “Without swift action, we expect the effects of this toad to be devastating. It could disrupt food chains and cause native predators, prey, and competitors to decline or even go extinct.”



The arrival of the toad is the latest blow in the battle to preserve Madagascar, whose rainforests continue to be heavily logged and amphibians are already threatened by a global disease wiping out frog and toad populations.

Among the 300 species of frogs on Madagascar, nearly all are endemic, meaning they are found nowhere else in the world and have little defence against invasive species. Scientists are concerned that the Asian toad will spread diseases to these native amphibian populations.



“Despite its heavily degraded state Madagascar still has a large number of endemic species likely to be impacted by the toad. Toads will impact food chains from both the top and the bottom, either of which could eventually affect the ecology across much of the country,” warns the report, by Pete McClelland, James T. Reardon, Fred Kraus, Christopher J. Raxworthy and Christian Randrianantoandro and funded by conservation groups including the Amphibian Survival Alliance.

The report also warns of the “significant and lethal” threat that the Asian toad poses to human health, with reported cases of death and cardiac arrest in Laos. This is of particular concern in Madagascar, which has an extensive rural population where frogs are consumed as a regular part of the diet.

Failure to tackle the spread of the toad will also have economic impacts, the report warns. Loss of biodiversity could undermine the island’s valuable environmental tourism industry, and biosecurity concerns would affect trade through possible restrictions on exports.

The scientists also warn that a decrease in predators due to toad poisoning would lead to an increase in the numbers of black rats. This could have an impact on human health through the spread of disease, and also economic consequences as stored food supplies are lost and commercial goods and equipment damaged.

The report recommends a complete eradication of the toads from Madagascar, which would “eliminate all possible ecological, economic and social impacts the toads may have ... with no long-term cost implications other than ongoing biodiversity improvements.”



Facebook Twitter Pinterest Researchers and field technicians measure and sex the invasive and toxic Asian toad to understand the impact of different eradication methods. Photograph: James Reardon/ASA

A team of scientists has been working with local technicians, students and communities on small-scale eradication trials since January. Methods that have shown success involve manual removal, trapping with drift fences, tadpole trapping, removing the toxins from the toads and using them as a lure, and spraying them with citric acid, which has resulted in a 100% mortality rate.



They now want to roll these techniques out at a greater scale of around 20-30 square kilometres, to prevent the toads from reaching the Pangalanes system. At the same time, “rapid decisions” must be made on a more long-term, widescale strategy by government and leadership bodies, they say.

But the report acknowledges that the eradication of an entire amphibian species has never been achieved on this scale. Success would depend on three things: detection methods that would pick up every animal across the entire area; toads being captured and removed faster than they breed, and no further toads being brought into the country.

The report puts the cost of the programme at $2m-$10m. “Such an extreme eradication effort will be extraordinarily difficult to organise considering Madagascar’s limited resources,” the authors warn.

“Considering the broad range of biological and economic negative impacts that are expected from this toxic toad, future generations will be furious, should we not make an eradication effort now, while there is still a chance of success,” said Chris Raxworthy, herpetologist and co-author. “We do not want to look back 20 years from now and wonder what Madagascar would be like if we had addressed this issue properly.”