Experts say riverbank infestations of fire ants are exploding south of Brisbane, and there’s a risk the venomous pests could spread further through flooding.
Reece Pianta from the Invasive Species Council said the “very dense infestation” is growing along parts of Logan River, with thousands of nests discovered by Cedar Grove Landcare Group while undertaking recent restoration works.
The fire ant hotspot was recently discovered by a Landcare group working in the Logan region. (Supplied: Invasive Species Council/Cedar Grove Landcare)
He’s warning heavy rain this summer could exacerbate the “serious problem” because, not only can fire ants fly through the moist air in mating season, but they also have the ability to join together and create a floating raft to survive.
“[They] can lock their legs together and form a big raft — a ball of fire ants — and basically carry the queen and the brood downstream with the floodwaters,” he said.
“When they find dry land, as the water recedes, they can essentially establish a new colony.”
Fire ants are only about 2mm to 6mm in size and have a reddish-brown colour. (Supplied: Invasive Species Council)
He said that makes the Logan River infestations — between the suburbs of Cedar Grove and Allenview — so dangerous, with heavy rain opening the door for “whole mature colonies” of fire ants to spread into new places.
How do fire ants survive flooding?
Cedar Grove Landcare president Rachel Hughes said the “tricky little creatures” will rotate around in the raft to keep the queen safe as they travel along the top of the water.
A raft of fire ants on the Gold Coast, pictured in January last year. (Supplied: Invasive Species Council)
“[With] so many thousands of nests on the Logan River at the moment, it’s a really scary thought,” she said.
“All those nests could move further in [and] flush downstream toward the city and Moreton, and infest new areas.”
While other ants exhibit similar rafting techniques, fire ants are especially good at it because of their South American homeland.
Fire ants are a threat, even in wet weather, because they can build rafts to float on floodwaters. (Supplied: stevenw12339)
Mr Pianta said they’ve been found over there “forming massive, multi-colony-sized rafts”, with the pests adapting to survive flood events.
“Inadvertently, we’ve found a species that is almost perfectly evolved to infest and spread on the continent of Australia,” he said.
“This is why they’re such a problem.”
Reece Pianta said fire ants can hitch a ride in carrier materials, as well as an ability to band together to float through floods. (Supplied: Invasive Species Council)
David Brennan runs a rural livestock business over several properties, including one on a junction linking Logan River to a smaller creek, and has been battling the pests for years.
“I first reported fire ants in 2015, but believe I was poisoning them before this time,” he said.
“I recall that the response by fire ant officers at that time was excellent — they’d be out here in a flash.”
The property sits on the junction of a smaller creek and Logan River, meaning floodwaters will back-up and sit stagnant for days. (Supplied: David Brennan)
In the 2017 and 2022 floods, water rose up then sat “very still”, with Mr Brennan’s land proving “to be an ideal drop-off zone for fire ants”.
“Remarkably, the water just backs up and stays there for days,” he said.
Fire ants, which grow colonies inside their nests, are an invasive species. (Supplied: Invasive Species Council)
Mr Brennan saw a huge increase in fire ant nests, recounting the painful blisters he suffered for several days as a result of their bites.
“I have been stung several times,” he said.
A huge fire ant nest found in south-east Queensland, sitting next to a jerry can for scale. (Supplied: Cedar Grove Landcare)
How do they spread?
Mr Brennan had to stop moving hay around his property when fire ants began nesting on-site.
Similar action has been mirrored in northern NSW, where a three-month ban has been imposed on turf imports from parts of south-east Queensland.
Mr Pianta said that’s because turf and hay are “high-risk carrier materials”, making it easy for fire ants to spread if they manage to nestle inside.
Fire ants, pictured here feeding on a dead grasshopper, can hitch a ride inside carrier materials. (Supplied: Invasive Species Council)
He said landowners, as well as a number of businesses operating near the river, will need to remain vigilant.
“It was pretty alarming to hear about the intensity of those infestations, and its closeness to the riverbank,” Mr Pianta said.
He said it shows how important suppression zone work is, and that “ultimately fire ant eradication means we’ve got to treat every hectare of land”.
Fire ants’ ability to handle wet weather could also impact how quickly they spread, with heavy rain usually followed by a mating season.
Rachel Hughes takes bait with her when walking her dog, treating fire ant nests as she goes. (Supplied: Cedar Grove Landcare)
“The next thing you know — three, 10, 20 kilometres away — you’ve got fire ants, because they go up into the air to mate and drop down into an open area that’s appropriate,” Ms Hughes said.
“Residential development, construction sites, sports fields and school grounds are perfect places for fire ants to establish and spread.
“We really need to be on the front foot.”
Why are fire ants dangerous?
Fire ants pose a threat to both humans and animals, with reports of nests attacking horses that drink from the Logan River.
There have been reports of nests attacking horses that drink from the Logan River. (Supplied: Invasive Species Council)
“We see this a lot with larger animals, and they can have the same kind of anaphylactic reaction that humans can, but we know that fire ants are also pretty devastating to insect life, lizards, frogs and other smaller animals,” Mr Pianta said.
“They’re an ecosystem changer, in terms of how they [impact] the ecology of an area.”
Fire ant venom can be severe and, in overseas cases, has proved fatal in the past.
A person monitoring fire ant baits near an open nest. (Supplied: Johan Augustin)
Scientists from the government’s eradication team have aerial technology and on-site researchers working on Mr Brennan’s farm, where different treatments are being trialled to eradicate the hotspot.
“They may still be here in twelve months’ time,” he said.
“[You should] report suspect mounds to 132 268 [and] look out for each other, especially children, because fire ants are bloody serious if they bite you.”
Fire ant venom can be dangerous for both humans and animals. (Supplied: Invasive Species Council/Murray S. Blum)
Fire ant infestations don’t “look like the traditional volcano-shaped ant’s nest”, making them difficult to identify, according to Ms Hughes.
She said the pests are “everyone’s problem”.
It’s important to know what a fire ant nest looks like, so locals can report sightings and the area can be treated. (Supplied: Invasive Species Council)
“If we don’t do something now, the Australian way of life is over — and I know that sounds dramatic but it is actually possible, these fire ants could colonise nearly the entire country because the conditions are right,” Ms Hughes said.
How to treat fire ants
Free bait, which Mr Pianta said has been specially designed to target fire ants, is available from the government.
Free bait has been specially designed to target fire ants. (Supplied: Johan Augustin)
But he and Ms Hughes both want to see more support rolled out for larger landholders, particularly primary producers living along the Logan River, to develop more systematic suppression strategies.
“We want to eradicate these things over the next decade,” Mr Pianta said.
“[Some landholders] are not aware of the infestation, so it’d be really helpful if they could get some assistance to have fly-overs to tell them how many nests are on their property [and] in actually treating it,” Ms Hughes added.
“If we take our foot off the pedal now, we’re going to lose the battle.”
