Red imported fire ants (Solenopsis invicta) are a highly invasive species of ant native to South America. Unlike other ants, which can be helpful decomposers and seed storers in our gardens, these small, reddish-brown ants are notorious for their aggressive behaviour and painful stings. First detected in Australia in Brisbane in February 2001, red imported fire ants likely arrived via shipping containers from the United States. Since then, they have spread across parts of southeast Queensland and northern New South Wales, posing serious threats to biodiversity, agriculture and public health.
Why Are Fire Ants a Problem?
Fire ants are more than just a nuisance; they are considered a ‘super pest’ and one of the worst invasive species globally. Their stings, said to resemble a burn, can cause painful pustules and, in rare cases, life-threatening allergic reactions or death. The ants’ presence can also force the closure of public spaces such as playgrounds and seriously disrupt our outdoor lifestyles, making BBQs, picnics and gardening unpleasant and risky.
Environmentally, the presence of red imported fire ants has a negative effect on native wildlife. When a nest is disturbed the ants swarm and attack on mass. Slow-moving animals including frogs, reptiles, koalas, echidnas and turtles are at particular risk. The threat in Australia is significant, as it is estimated that 95% of Australia’s land mass could provide suitable habitat for the pest.
How Do Red Imported Fire Ants Spread?
Fire ants spread through both natural and human-assisted means:
- Human transport: Soil, mulch, potted plants and machinery can unknowingly carry ants or queens to new locations.
- Nuptial flight: Fertile males and females are winged and can fly up to 5 km to establish new colonies. The flights usually occur after rain.
- Rafting: Fire ants can float on floodwaters, allowing them to travel and colonise new areas following heavy rain and flooding.
This mobility makes containment extremely challenging, especially in urban and peri-urban environments.
How to Identify Fire Ant Nests
Fire ant nests are typically found in open, sunny areas such as lawns, paddocks and on roadsides. Key features of the nests include:
- They are dome-shaped mounds up to 40 cm high.
- The nests have a ‘messy’ structure with no visible entry or exit holes (unlike the nests of other species of ants).
- The mounds often appear after rainfall or irrigation as the ants build them up to protect the queen.
Disturbing a mound can trigger a mass swarm of aggressive ants, so taking care when trying to identify the nests is essential.
How to Identify Red Imported Fire Ants
Red imported fire ants vary in size from 2 to 6 mm within a single colony, a unique trait among ant species. They have:
- copper-brown heads and bodies, with darker abdomens;
- two prominent nodes between the thorax and abdomen;
- aggressive behaviour, with ants swarming on mass and stinging rapidly when disturbed.
Their sting causes a burning sensation, likened to a burn, followed by white pustules that can become infected if broken.
Preventative Actions to Stop the Spread
Preventing fire ant spread requires both community awareness and responsible gardening practices. Under the Queensland biosecurity act, all Queenslanders have an obligation to make sure they do not spread fire ants. Resources are available for businesses who handle or transport soil, mulch and plant material.
Some actions that gardeners can take to help control the spread of red fire ants:
- Be aware of the current spread of imported red fire ants in Australia, and the fire ant suppression area.
- Inspect soil, mulch and plants before moving them between properties or when they arrive in your garden.
- Avoid disturbing suspected mounds.
- Seal cracks and crevices in buildings to prevent indoor nesting.
- Use targeted bait treatments rather than broad-spectrum pesticides to protect native ants; home treatment kits are available for home gardeners within the fire ant suppression area.
- Report sightings promptly.
What to Do If You Detect Red Imported Fire Ants
If you find a suspected red imported fire ant nest:
- Do not disturb the nest.
- Take clear photos or videos from a safe distance.
- Report immediately via the National Fire Ant Eradication Program:
- Call 13 22 68 (132 ANT).
- Submit a report online at fireants.org.au
Authorities will assess your report and may send a treatment kit or dispatch officers to manage the infestation. Prompt reporting helps prevent further spread and supports national eradication efforts.
Red imported fire ants are a formidable threat, and it will take government, industry and community vigilance to protect our gardens and wider environment from their effects.
Resources
https://www.youtube.com/watch?v=RHxjEJURSW0
Photo credits: National Fire Ant Eradication Program