BRISBANE, Australia — Australia's ambitious campaign to eradicate the invasive fire ant, one of the world's most aggressive pests, is facing growing scrutiny as new research suggests the very tactics being used could be accelerating the insects' spread across the continent.
The National Fire Ant Eradication Program, launched after the ants were first detected in a Brisbane suburb in 2001, has ballooned into the largest such effort globally, targeting an infestation that now spans more than a million hectares in South East Queensland. Authorities have relied on broadcast baiting, dispersing pesticide-laced granules over vast landscapes to collapse fire ant colonies from within. But according to a recent analysis by ecologist Luke Shoo, published in The Conversation, this scorched-earth approach may be creating ecological vacuums that allow the resilient fire ants to thrive unchecked.
Fire ants, scientifically known as Solenopsis invicta, originated in South America and earned their name from the intense burning sensation of their stings, which can cause severe allergic reactions in humans and pose significant threats to native wildlife. The pests have infiltrated Australia via cargo ships on at least nine occasions, with officials successfully quashing eight early detections. The ninth, uncovered in 2001 near the Port of Brisbane, has proven far more stubborn, expanding rapidly through urban, rural, and industrial zones.
"These aggressive South American ants... pose risks to many native species – and to human health," Shoo wrote in his article, highlighting how the ants disrupt ecosystems by outcompeting local insects and preying on small animals. Since 2001, Queensland authorities have treated affected areas multiple times with insect growth regulators like pyriproxyfen and S-methoprene, chemicals embedded in corn grit and soybean oil baits. Worker ants carry these back to nests, where larvae ingest them and unwittingly distribute the toxins through liquid feeding, leading to colony collapse over several weeks.
This method has shown success in smaller outbreaks, limited to under 10,000 hectares, where comprehensive coverage ensures no nests escape. However, Shoo's research indicates that over larger scales, the indiscriminate nature of broadcast baiting wipes out not just fire ants but also their natural competitors and predators, paving the way for easier expansion. "When large areas are baited, the result is an ecological vacuum. Competitor species are wiped out and hardy fire ant survivors can press forward," he explained.
Fire ants, described by Shoo as a “weedy” species, flourish in human-altered environments such as roadsides, paddocks, and industrial sites. When baits are applied along infestation edges, they decimate rival ants and invertebrates, leaving open territory for fire ant queens to establish new colonies. In undisturbed areas like dense forests with thick leaf litter, native species mount stronger defenses, making it harder for fire ants to gain a foothold.
Newly mated fire ant queens are particularly vulnerable during their dispersal phase, when they must fly, mate in mid-air, and land to found a colony. In natural settings, they face predation from meat ants (Iridomyrmex species), green-headed ants (Rhytidoponera metallica), the invasive coastal brown ant (Pheidole megacephala), spiders, lacewings, earwigs, birds, and beetles. "These defenders should be our key allies in the fight against fire ants," Shoo argued. Yet the broadscale baits harm these allies too, as many non-target species consume the granules.
Historical efforts in the United States, where fire ants have been combated since the 1950s, offer sobering lessons. In Georgia, a large-scale baiting initiative initially appeared successful, but fire ants reemerged within 14 months at higher densities and faster spread rates than native ants. Florida's experiences similarly show new infestations popping up in disturbed zones where competitors have been eliminated. "In southern US states, authorities tried broadcast baiting for decades before giving up," Shoo noted, underscoring the challenges of managing infestations beyond a certain size.
Queens add another layer of resilience to the problem. After mating, a fire ant queen burrows into the soil and seals her chamber for up to four weeks, surviving on fat reserves while laying her first eggs. During this claustral period, she and her nascent colony are impervious to surface-deposited baits. "While newly mated fire ant queens are vulnerable to predators, they are not vulnerable to baiting," Shoo pointed out, a quirk that allows undetected spread even amid intensive treatments.
At over a million hectares — 100 times larger than any previously eradicated infestation — South East Queensland's scale renders perfect bait coverage practically impossible. Officials must retreat areas repeatedly, but gaps inevitably occur, especially in sprawling urban-rural interfaces. Shoo's work suggests that continuing this strategy not only fails to contain the ants but may exacerbate their invasion by removing natural barriers.
The program's controversies extend beyond ecology. Some communities in affected areas, including suburbs around Brisbane, have expressed unease over the widespread chemical use, leading to tensions with authorities. Organic farmers face particular hardships; exposure to certain baits, including those with genetically modified components, can jeopardize their certifications. "The baiting program is becoming controversial. Some communities are not comfortable with the approach, causing tension," Shoo reported, while emphasizing the need for strategies that rebuild public trust.
In response to these challenges, Shoo advocates for an integrated pest management shift away from blanket baiting. One proposal involves targeting individual nests with precise methods, such as injecting boiling water or applying fipronil directly, which minimizes collateral damage. "When nests are found, they can be removed by injecting hot water into the nest, or by applying pesticides such as fipronil. These scientifically robust methods avoid the widespread collateral damage from broadcast baiting," he suggested.
Precision baiting could further refine efforts, using underground stations or fire ant-specific containers to deliver growth regulators without harming other species. Enhancing landscape resistance is another pillar: protecting shrub-covered areas and thick leaf litter habitats bolsters native defenders. Emerging technologies, including viruses for biocontrol, genetic modifications, and chemicals that disrupt ant communication, warrant swift evaluation for safe integration into the toolkit.
"There’s now no chance we can eradicate these ants using broadcast baiting," Shoo concluded, urging a pivot to multifaceted approaches. "A better option is to use a number of strategies for integrated pest management." Such changes, he argued, could reduce costs, preserve biodiversity, and foster community support for what remains a protracted battle.
As fire ants continue to encroach on new territories in Queensland, the stakes are high. The infestation threatens agriculture, recreation, and public safety, with stings sending thousands to hospitals annually in infested regions. Officials from the Queensland Department of Agriculture and Fisheries have not publicly responded to Shoo's critique, but program updates indicate ongoing refinements, including increased surveillance and community reporting hotlines.
Looking ahead, experts like Shoo stress that aligning eradication with ecological realities is essential. "If we fight against nature, we will lose," he warned, encapsulating the broader implications for invasive species management worldwide. With fire ants' potential to spread further south and west, Australia's response could set precedents for global pest control, balancing aggressive intervention with sustainable stewardship.