- Over the last two decades, Indigenous rangers in Australia’s Tiwi Islands came together with scientists, government actors, NGOs and private enterprise to eradicate the invasive tropical fire ant species from Melville Island.
- The species threatens small animals, vulnerable sea turtle hatchlings and nesting birds, according to some studies.
- The eradication program included locating the ant nests, poisoning them at small-scale with Amdro, an insecticide bait, and then monitoring sites to ensure the eradication was complete.
- A member of the eradication effort hopes lessons of the Tiwi eradication program could be replicated in other regions of the country, like Ashmore Reef.
DERBY, Australia — While Spanish sailors packed in dirt to stabilize the bottom of ships sailing from the Americas in the 16th century, they were unaware that they were also helping tiny stowaways aboard. Research suggests that tropical fire ants sailed across the Pacific Ocean, joining Europeans over the centuries as they landed and colonized landmasses across the world.
Then, in the early 2000s, tropical fire ants (Solenopsis geminata) were detected on Melville Island in the Tiwi Islands, a picturesque archipelago off the coast of Darwin, the capital of Australia’s Northern Territory. Here, they were able to flourish, according to researchers, and have since become naturalized in parts of the Australian tropics while dominating the environment, eating small mammals, and potentially deterring nesting birds.
“The ants have a huge impact on native birds and animals on the Tiwi Islands,” said Stanley Tipungwuti, a ranger on the islands where most identify as Aboriginal or Torres Strait Islander.
But after two decades of effort, and the work of the Tiwi Ranger team, tropical fire ants are deemed no more on Merville Island: In 2025, the species was completely eradicated, according to Ben Hoffmann, who was part of the eradication program from its inception. That same year, the Tiwi Island Rangers received the Territory Indigenous Natural Resource Management Award in Darwin for their efforts.
Hoffmann, principal research scientist at Australia’s national research agency, CSIRO, now runs Myrmex, a consultancy specializing in biosecurity, especially invasive ants. He told Mongabay that the impacted area this project addressed — at 1,535 hectares (3,790 acres) — is large even on a global scale.
“There have been very few tropical fire ant eradications around the world, and when they have been done, they have been incredibly small, from one nest to one hectare [2.47 acres] or so,” he said. “After we began, we realized we had to change our methods from broadscale treatment to painstakingly locating individual nests and poisoning them … It is an amazing feat.”
Nigel Andrew, an entomologist and chair of science at Southern Cross University in Australia who was not involved in the project, echoed these sentiments when speaking to Mongabay.
“This is one of the top three eradications of any invasive ant species worldwide,” Andrew said. “For something like this to be successful, there needs to be complete, one hundred percent eradication, and a guarantee that all the nests have been destroyed, which can take years as you systematically move through the sites. Only a concerted effort over a long time can make something like this possible.”
Investing in rangers
There was no ranger team in the Tiwi Islands at the time of the tropical ant incursion, and the invasive species problem was initially addressed by the local council and housing operations.
However, throughout the past two decades and with the assistance of the government’s Indigenous Rangers Program, which assists First Nations peoples in managing their lands, the Tiwi Ranger team was born and grew. Over time, more than 40 rangers were involved in identifying and eradicating tropical fire ant sites.
Tipungwuti was one of them.
“[The ants] form huge colonies and can really impact the native birds, the small mammals and also sea turtle hatchlings,” Tipungwuti told Mongabay. “They can do a lot of damage and they also can cause red, itchy lumps on the skin if they bite you. Some people can have allergic reactions and can get sick very quickly.”
Studies on the environmental impacts of the ants in the Tiwi Islands and similar landscapes in Australia are scarce. What is available shows that tropical fire ants target and attack the hatchlings of both birds and reptiles where they have colonized around the world.
In the Tiwis, newly hatched tiny sea turtles struggling out of the sand to make their way to the ocean are at risk, said rangers. Each year, the islands play host to the nesting of four sea turtle species, all of which are considered endangered or vulnerable by the Australian government: The olive ridley (Lepidochelys olivacea), the green (Chelonia mydas), the flatback (Natator depressus) and the hawksbill (Eretmochelys imbricata). The hawksbill, while considered vulnerable in Australia, is categorized as critically endangered globally in the IUCN Red List. IUCN is the global wildlife conservation authority.
Tipungwuti said that the Territory Indigenous Natural Resource Management Award was a recognition of all the rangers who have taken part in the eradication. “We all felt so proud, because all the hard work of all those rangers over twenty-two years paid off. It was an amazing achievement.”
Combing through backyards and insecticide
Tipungwuti said that one of the key challenges during the project involved locating the ant nests, poisoning them with Amdro, an insecticide bait and then monitoring sites to ensure the eradication was complete. An all-community effort was essential, he explained, and included input from the Tiwi Plantations Corporation, the largest Indigenous agricultural venture in northern Australia, which is also owned by the Tiwi people.
The active ingredient in Amdro is hydramethylnon, which has been shown to negatively affect other insects, such as cockroaches if used in a broadscale manner. A 2010 study in Hawaii showed that use of the poison can also lead to a decline in non-target ant species. To mitigate risk to the wider ecosystem in the case of the Tiwis, baits were concentrated in certain areas and rangers closely monitored sites.
Andrew said that although pesticides like Amdro can affect non-target species, their use in the Tiwis has been at a relatively small scale, allowing populations of non-target species to recover.
“In most cases, removing fire ants allows native insects that were competing or predated on by fire ants to recolonize affected areas over a few years,” he said.
Moreover, given that most granular bait was applied by hand, Andrew said that the risk of pesticides entering the groundwater is significantly reduced. “Any runoff would be limited and localized, as treatments are targeted to known nesting areas,” he said.
Hoffmann said that while in most circumstances a project like this would not have been achievable, there were some key elements that favored the Tiwi project.
“The first thing is that the tropical fire ant finds it difficult to survive in natural, or undisturbed habitats,” he explained. “In the case of the Tiwis, this meant the focus was on disturbed areas, such as around communities and along roadsides. The nice thing is that Melville Island is a largely intact environment.
“Secondly, public support meant we could cover every square inch of ground for years. There were the yards of some homes that we went through up to fifty times,” Hoffmann said. “You need a lot of public goodwill to be able to access people’s properties like this.”
Lessons for the rest of the world
Hoffmann said that some of the lessons of the Tiwi eradication program could be replicated in other parts of the country, like Ashmore Reef.
The Ashmore Reef Marine Park, lying in the Timor Sea with islands classed as a RAMSAR site, are an important breeding ground for sea turtle species, especially the green turtle. Here, tropical fire ants have colonized the reef’s land areas and a preliminary assessment suggests they are causing damage to migratory seabirds and turtle nests through predation of turtle hatchlings and vulnerable birds like the red-tailed tropicbird (Phaethon rubricauda).
“There is already work underway [to eradicate them], but it is a much more delicate situation than the Tiwis as you cannot drench the ground with chemicals because of the risks to the groundwater,” he said. “All the area also needs to be treated simultaneously, because tropical fire ants are across the entire landmass.”
As an alternative, he said, there is research being done by groups such as Australia’s Commonwealth Scientific and Industrial Research Organisation into developing genetic-based baits that will aim to target specific species; in this case, tropical fire ants.
Back on the Tiwis, Tipungwuti said that the focus of the now 15-strong ranger team is turning to other feral animals such as pigs (Sus domesticus) and cats (Felis catus); both of which have impacted native species through predation and the destruction of habitat.
The team will also undertake constant observation and monitoring to prevent another fire ant incursion. In this, they will be supported by a biosecurity officer employed by the Tiwi Land Council to ensure that any freight coming to the islands is checked for invasive species.
Hoffmann said that this role is essential to ensuring that the tropical fire ant, or any other species, is kept from the Tiwis. “Tropical fire ants arrived on the Tiwis, because there was no biosecurity,” he said. “If we had something like this in place then they may not have ever arrived there.”
Andrew, the chair of science at Southern Cross University, said the key in any eradication is to get in early, have sound biosecurity measures, and excellent communication and partnership with the local community
“There needs to be constant vigilance to ensure there is no future incursion,” he said.
Banner image: Tropical fire ants (Solenopsis geminata). Image by Francois Brassard.
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Citations:
McGlynn, T. P. (1999). The worldwide transfer of ants: geographical distribution and ecological invasions. Journal of Biogeography, 26(3), 535–548. doi: 10.1046/j.1365-2699.1999.00310.x
Plentovich, S., Swenson, C., Reimer, N., Richardson, M., & Garon, N. (2010). The effects of hydramethylnon on the tropical fire ant, Solenopsis geminata (hymenoptera: formicidae), and non-target arthropods on Spit Island, Midway Atoll, Hawaii. Journal of Insect Conservation, 14(5), 459–465. doi: 10.1007/s10841-010-9274-6
Mott, R., Hodgson, J. C., Herrod, A., & Clarke, R. H. (2020). Nest-site didelity in Red-tailed tropicbirds informs costing a localised ant baiting strategy at Ashmore Reef. Emu-Austral Ornithology, 120(3), 269–273. doi: 10.1080/01584197.2020.1787847
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Cite this article
Nick Rodway (2026). Tiwi rangers eradicate invasive tropical fire ants in Australia’s Melville Island. Mongabay Conservation news. DOI: https://doi.org/10.66709/news-321598Credits
