The end to backyard play? Red imported fire ants in Sydney

Feral Herald |

A colony of red imported fire ants was discovered in Port Botany, Sydney, in November.

If they have spread and are not eradicated, life in Sydney and other large parts of Australia will be irrevocably changed.

Imagine not being able to walk around in thongs or children not being able to play in backyards, and councils paying millions of dollars each year to keep the ants out of parks. Imagine ground-nesting birds and lizards and other wildlife being stung to death by thousands of tiny ants. Baiting red imported fire ants and repairing the damage would cost billions of dollars annually.

This is the fifth time these ants have established in Australia. The Queensland government has been attempting to eradicate them from South East Queensland (parts of Brisbane and to the south and west of Brisbane) and Gladstone.

Biosecurity officers are baiting the Port Botany colony and searching within a 2 kilometre radius for other nests. Winged ants were found in the  nest, so it is possible they have spread into other areas. Queens fly an average 500 metres to set up a new nest.

Fire ants are up to 6mm long and reddish-brown in colour. Report suspected sightings to the Exotic Plant Pest Hotline on 1800 084 881. Photo: April Noble,,
Red imported fire ants (Solenopsis invicta) are very small ants between 2 to 6mm long, reddish-brown in colour with a dark abdomen. Report suspected sightings to the Biosecurity Hotline on 1800 084 881 (NSW) or 13 25 23 (Queensland).
Photo: April Noble,,

Sydneysiders in the vicinity can help by checking if the ants they find in their backyards and on footpaths and in parks are red imported fire ants.

This incursion and the others in Queensland show there are major gaps in biosecurity.

It is thought the Sydney ants arrived at least 6 months ago, probably on a cargo ship. Their discovery was a stroke of good luck – not due to regular surveillance but in response to checks for another recent unwelcome arrival (of a giant African snail).

How many more colonies might be out there – breeding and spreading – due to a lack of systematic surveillance?

About red imported fire ants

Red imported fire ants are native to South America, but have spread to the United States, China, Taiwan, the Philippines and Australia.

Red imported fire ants are omninvores, preying on invertebrates and vertebrates and also eating plants and honeydew. They are highly aggressive, with a venomous sting used to kill their prey and defend their nest, and they swarm in large numbers to attack any animal disturbing their nest. Although they are tiny (2-6 mm), their sting and high numbers enable them to overwhelm and kill prey much larger than they are.

Red imported fire ants colonies typically contain 200,000 to 400,000 workers, although some super colonies have many millions. There are two forms – colonies with a single egg-laying queen (monogyne) and those with multiple reproductive queens (polygyne). The multi-queen colonies (sometimes with several hundred queens) reach higher densities than single-queen colonies – up to 50 million ants per hectare. They mostly spread by budding – a new queen mates within the nest and then walks a few meters with a few workers and brood to set up a new nest. In the single-queen form, the virgin queens and the males mate in the air, and the queens fly 500 metres or so to build a new nest.

The ants discovered at Port Botany were in a single-queen colony while Queensland has both forms.

Eradicating red imported fire ants 

The Port Botany colony is the fifth time red imported fire ants have established in Australia. Two colonies were discovered in the Brisbane area in 2001 and two in Gladstone in 2006 and 2013. Genetic studies show they have each resulted from separate arrivals.

There are currently three eradication programs in Australia for red imported fire ants: in South East Queensland (which is officially a containment program), Gladstone and, now, Port Botany. The costs for the programs are shared between state and federal governments. So far, the Queensland programs have cost state and federal governments about $300 million, and achieved the eradication of the 2001 Port of Brisbane and the 2006 Gladstone incursions.

Location Year detected Extent Current status
Port of Brisbane 2001 470 known colonies, >12,000 hectares Eradicated (2005)
South East Queensland 2001 Initially discovered in Wacol southeast of Brisbane and spread over >300,000 hectares. Containment (with view to eradication)
Gladstone 2006 14 known colonies (but possibly 100), >1000 hectares treated. Eradicated (2007)
Gladstone 2013 80 known colonies spread over 4600 hectares Eradication underway
Port Botany, Sydney 2014 1 colony detected Eradication underway

To achieve eradication requires detecting all colonies (as early as possible), destroying those colonies and preventing red imported fire ants spread to new areas by humans. In Queensland, methods used to detect colonies include aerial photography (with high definition visual, near infrared and thermal cameras to detect mounds), and ground searching, including with sniffer dogs, which are sensitive enough to detect single ants. Educating the community to check for and report suspicious ants and avoid spreading them (eg. by moving soil) is essential.

The best method for destroying red imported fire ant colonies is a bait with delayed toxicity to allow the workers to take it to the queen. There are several toxins in use.

The consequences of failure

What would Australia be like if eradication fails or if more red imported fire ants arrive in Australia?

About one-quarter of Australia, including much of the populated coastal belt and wetter inland areas, is climatically suitable for red imported fire ants. If any of the eradications fail, the ant is likely to spread to these areas over subsequent decades through the regular movement of people and goods.

Environment: Fire ants have more ecological impacts than most ants because they reach extremely high densities. An assessment of their likely impact on 123 animals in southeast Queensland predicted population declines in about 45% of birds, 38% of mammals, 69% of reptiles and 95% of frogs. By reducing plant populations and competing with native plant- and insect-eaters they can affect entire ecosystems. Plants may face risks from red imported fire ants disrupting seed dispersal, pollination and germination.

Health and lifestyle: When a red imported fire ants mound is disturbed, thousands of ants swarm to the surface and repeatedly sting the intruder. This makes infested parks and gardens uninhabitable. In the US, 30 to 60% of people in infested areas are stung each year. The stings are painful and the alkaloid venom causes pustules and, in some people, allergic reactions. More than 80 people in the US have died of anaphylactic shock[1]. Some elderly people in nursing homes have died after mass stings.

Economic: By mid-2014, federal and state/territory governments had spent $300 million attempting to eradicate red imported fire ants. Additional costs have been borne by local governments, energy utilities, industry and others. Although expensive, this is far less than the costs of failing. Modelling by the Queensland government indicates that in South East Queensland alone fire ants would impose costs of about $43 billion over 30 years[2]. In the US the ant costs $7 billion a year in damage and control[3]. Among the costs are damage to infrastructure (roads, footpaths and electrical equipment) and to farming enterprises. red imported fire ants damage crops, rob bee-hives and kill newborn livestock. During dry times, red imported fire ants dominate the margins of dams and livestock cannot reach water without being seriously stung.

Biosecurity gaps

Of all the invasive species that should be kept out of Australia, red imported fire ants are one of the most serious and costly.

The increasing rate of red imported fire ants incursions and interceptions shows there are serious gaps in Australian biosecurity that undermine our chances of becoming red imported fire ant-free, putting at risk the more than $300 million already spent trying to eradicate them.

Timeline of incursion detections (bold) and interceptions 

2001 Port of Brisbane and South East Queensland
2006 Gladstone
2009 4 interceptions
2011 3 interceptions
2013 Gladstone
2014 Port Botany, Sydney

Risk assessment and planning: There hasn’t been enough being done to identify and close off pathways for red imported fire ant arrival and spread in Australia, assess the biodiversity that is at risk and how to protect native species from these ants.

Surveillance: The fact that many incursions are not detected until many years after they arrive shows that surveillance in high risk areas such as ports is inadequate. The first two incursions in 2001 were not detected probably for at least a decade, the second Gladstone incursion for probably 3 years and the Port Botany incursion probably for 6 months or more. Most are discovered by chance rather than through systematic surveillance.

Funding for eradications: The eradication programs in Queensland have suffered from too little and short-term funding. Eradication efforts tend to fail if the budget is tight. The southeast Queensland infestation was almost eradicated in 2003 but the failure to conduct broad enough surveillance allowed the infested area to double between 2004 and 2010. There is currently no guaranteed long-term funding for the eradication programs.

Public education: The community is a largely untapped asset for detecting invasive species such as tramp ants, and much more could be done to educate the public about what to do when unfamiliar species are encountered. Most tramp ant incursions are detected by chance by members of the public.

More info

Other sources

1 Rhoades R, Stafford C, James F. 1989. Survey of fatal anaphylactic reactions to imported fire ant stings. Journal of Allergy and Clinical Immunology 84(2): 159-162

2 Antony G, Scanlan J, Francis A, Kloessing K, Nguyen Y. 2009. Revised benefits and costs of eradicating the red imported fire ant, Queensland Department of Primary Industries and Fisheries, Brisbane.

3 Lard C, Schmidt J, Morris B, et al. 2006. An economic impact of imported fire ants in the United States of America. Texas A&M University.

Feature photo: Red imported fire ants on a 10 cent coin. © The State of Queensland (Department of Agriculture, Fisheries and Forestry) 2010–2014.

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