Red imported fire ant

bites

stings

harms crops

harms people

harms wildlife

lives on ground

day active

different sizes

Red imported fire ant worker (© Mario David Bazan, Creative Commons License)

Red imported fire ant mound (© Alex Wild)

Scientific name: Solenopsis invicta

Size: 2-6 mm

Colour: reddish-brown, black gaster

General description: workers come in a large range of sizes (polymorphic). These ants are very aggressive and will bite and sting when disturbed. They may also make large mounds up to 40 cm high with no apparent openings in the top. It can be difficult to identify the difference between red imported fire ants and tropical fire ants. Red imported fire ants are much more aggressive their stings are more painful and result in blisters after 24 hours.

Habitat and nesting: the red imported fire ant is a ground dwelling species that builds it nests in mounds of earth up to 46 cm diameter in open pasture. In urban environments, the ant may nest under concrete foundations, paving, driveways or slabs. The ants’ excavations beneath such concrete slabs may cause them to sink or collapse causing damage. The ants have also been found nesting in electrical boxes. During periods of heavy rain, the ants may abandon their nests to seek higher ground, which may include movement into homes and other buildings.

Rate of spread: 10-40 m/year in Texas.

Distribution: see our invasive ant distributions page for the worldwide distribution of the red imported fire ant.

Red imported fire ant workers come in a large range of sizes (© Dini Miller, Virginia Cooperative Extension, Virginia Tech, and Virginia State University)

Red imported fire ant biting and stinging (© Alex Wild)

Global distribution of the red imported fire ant (© Pacific Biosecurity)

A winged red imported fire ant queen preparing to fly away to begin a new colony. Queens can build new colonies up to 2 km away from the nest where they were born (© Johnny N. Dell, BugwoodWiki)

PIAkey: Solenopsis invicta (see diagnostic characters tab)

AntWeb: Solenopsis invicta

eXtension.org: Identifying Fire Ants

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Fire ant stings are extremely painful (© State of New South Wales through NSW Department of Industry)

Social

These ants are well known for their extremely painful sting, which may cause a severe allergic reaction (anaphylactic shock) in some people. This species can make parks, beaches and other public areas they inhabit unusable and unsafe for children. 

More than 5 million people are stung every year in the United States and about 1% of those stung require medical attention due to an allergic reaction. More than 80 people have died as a result of red imported fire ant stings (usually due to an allergic reaction) in the United States alone.

Agricultural

Red imported fire ants collect and eat seeds and may attack fruits, new shoots and roots of plants, reducing crop yield. A single farmer from Alabama lost 200 citrus trees in one year.

Their painful sting makes harvesting some crops difficult as well. In China some rice paddies and orchards have been abandoned altogether due to these stinging pests.

The nest mounds they build may interfere with farm equipment and undermine the concrete foundations of buildings.

Environmental

Red imported fire ants appear to be responsible for the decline of many bird, reptile, amphibian and small mammal species, as well as many invertebrate species (insects and spiders).

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Red imported fire ants foraging on peanut butter in North Carolina, Vimeo video (© Eli Sarnat, Creative Commons Attribution, Share Alike CC BY-SA Licence)

Red imported fire ants can prevent pollinators from visiting crops (© Phil Lester)