Red imported fire ant

Red imported fire ants are tiny and difficult to distinguish from other tiny ants. The purpose of this page is not to identify them definitively but to rule out enough alternatives that an approach to the authorities is justified. Look for the following characteristics:

• The heads and bodies are reddish or coppery-brown with darker abdomens.
• The ants come in various sizes rather than one size only, or two. The size differences are not necessarily dramatic but are noticeable when many ants are present.
• The ants are aggressive, and sting in groups if a nest is disturbed. This is very telling characteristic.

The next two features are not especially important and require a microscope or strong hand lens to be detected:

• The thorax is separated from the bulge of the abdomen by two small narrow segments.
• The thorax has no spines.

The nests are useful for identification – see under Behaviour and Location.

The fire ant thorax lacks spines and there are two small segments with knobs separating it from the bulge of the abdomen. Photo: Eli Sarnat, PIAkey: Invasive Ants of the Pacific Islands, USDA APHIS PPQ, Bugwood.org

Workers vary from 2-6 millimetres long. Most people who learn about fire ants expect them to be large because the problems they cause are large, but they are very small.

The nests usually have no obvious entry or exit holes. They often appear as domes of bare earth. They can be up to 40 centimetres high, but may also be flat and look like a small patch of disturbed soil. They are usually placed in sunlit open areas such as lawns and pastures, or on road sides and fallow cropland. Open ground near water is a favoured location. If nests are kicked or poked with a stick the ants usually teem out to attack.

Fire ants will also nest under logs, garden materials, or in hay or mulch.

They readily use home gardens and sometimes enter houses where they are attracted to electricity, so they will crawl inside computers, air conditioning units and electrical switch units. The ants also gather inside outdoor infrastructure such as meters and pumps.

Fire ant nests can be flat, with only a subtle entrance. Photo: Leslie J. Mehrhoff, University of Connecticut, Bugwood.org

Fire ant nests can appear as mounds in lawns. Photo: Jake Farnum, Bugwood.org

When people are attacked they typically receive multiple stings, which burn or itch, and usually produce a weal and flare followed by a pustule a few hours or days later. These can last up to 10 days. People can be stung in parks, their own gardens, and in the home.

Pustules form after fire ant stings. Photo: USDA APHIS PPQ, Bugwood.org

Fire ants are established in South east Queensland where a massive eradication campaign is underway. Small populations have been eradicated from Sydney, Fremantle and Gladstone. They are regularly intercepted at Australian ports. In future they could turn up anywhere in Australia. They are especially likely to establish near ports and industrial zones in which international goods are unloaded. The community has an important role to play in detecting them. Around Brisbane many infestations have been detected by diligent (or besieged) members of the public.

Many small ants can be confused with fire ants, though most of them do not sting. Two introduced species are shown here, one because it is very common and one because it stings.

Argentine ants (Linepithema humile) are small (under 3 millimetres long) all the same size. Their abdomens are not darker than their heads and they do not sting. They march in trails several ants wide.

Argentine ants. Photo: Whitney Cranshaw, Colorado State University, Bugwood.org

Electric ants (Wasmannia auropunctata) sting, but they are smaller (under 2 millimetres long) and all the same size. Their abdomens are not darker and they do not produce earthen nests from which they launch attacks when disturbed. They are another invasive ant of grave concern that should be reported to authorities. See our electric ants profile page.

Electric ants. Photo: Eli Sarnat. Cite as: Eli Sarnat, PIAkey: Invasive Ants of the Pacific Islands, USDA APHIS PPQ | Bugwood.org

Fire ant stings cause burning or itching sensations that can last an hour. The sting of a single ant is usually mild, but victims of multiple stings can feel as if they are on fire. In rare cases an allergic response occurs, and this can be life threatening, requiring urgent medical attention.

It is not necessary to collect fire ants if you strongly suspect you have found them.

Think you’ve found red fire ants?

If you are in Queensland notify Biosecurity Queensland on 13 25 23 or complete the online fire ant notification form.

Elsewhere in Australia phone the Exotic Plant Pest Hotline: 1800 084 881.

Fire ants are very effective predators because they reach very high densities and sting prey in large numbers. In the United states they prey on hatchling alligators, freshwater turtles, sea turtles and ground-nesting birds. Deer produce more young in places where fire ants are controlled, and the ants can remove 75 per cent of invertebrates from invaded land, leaving behind far fewer insects for hungry birds and lizards. They do harm both as predators and competitors, displacing other ant species over wide areas. In Australia one high-level report warned in 2016 that ‘iconic birds like the bush stone-curlew, plumed frogmouth, rufous scrub-bird, superb Iyrebird and black-throated finch are at significant risk,’ and it mentioned as well the tiger quoll and echidna, reptiles, frogs, freshwater fish and butterflies. Animals not killed outright can experience ‘reduced weight, loss of digits, obscured vision or blinding and an inability for normal movement’. The ants do not invade intact forest, but they will forage up to 40 metres from forest edges.

On American farms they do some good, consuming pesky insects and weed seeds and aerating soil, but their downsides are enormous. They tunnel inside fruits and prey on seeds, sometimes destroying whole crops. Potatoes, eggplants, sunflowers and citrus are some of the crops hit hard. They swarm over and punish farm workers, who receive penalty rates to contend with them, if they are willing to contend with them. The ants rob bee hives. They ruin sprinkler systems and hoses. Their mounds damage harvesting machinery. Worst of all, they attack newborn livestock, sometimes killing foals, calves and chickens. Sluggish or immobile animals are stung around the eyes and blinded. Farmers have to poison ants in pens where stock give birth. In the USA, the ants cost $US7 billion each year in impacts and control.

In the United States, which acquired them decades ago, other problems they cause include computer failures, fires, potholes, uninhabitable parks, crop losses, More than 80 people have died from the stings, mainly of anaphylactic shock. In nursing homes a growing problem is elderly patients killed in their beds. One woman died in a house fire after the ants caused a short circuit. Electrical currents attract them and when one is zapped the pheromones it releases attract its comrades, until the masses of dead bodies trigger failures of light switches, air conditioners, traffic lights, pumps, meters, even car electrical systems. Americans spend more than $6 billion a year on the problems they cause.

Modelling by the Queensland Government indicates that in southeast Queensland alone fire ants would impose costs of about $45 billion over 30 years. In Australia they could cause an extra 140,000 medical consultations and 3000 anaphylactic reactions a year.