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How to identify it
- Workers in one nest vary in size and are dark reddish brown. Sources give different ranges: UC IPM says 1/16 to 1/5 inch, Kentucky 1/16 to 1/4 inch, and APHIS (covering both imported fire ants) 1/8 to 1/4 inch. Queens are about 3/8 inch.[1][2][7]
- Two nodes at the waist and 10-segmented antennae ending in a two-segment club; telling species apart takes magnification.[1][2]
- Undisturbed mounds are dome shaped and can be a foot high; on mowed lawns they may look like gopher mounds of loose soil. Kentucky and APHIS say mounds can reach 18 to 24 inches tall, and Kentucky says there is no noticeable entrance hole.[1][2][7]
- The quickest sign is behavior: workers swarm up and sting anything touching the mound. Kentucky calls this boiling out.[1][2]
- The feature that separates the red imported fire ant from other fire ants is three teeth on the front edge of the head (the native southern fire ant has two), best seen under a microscope.[1]
Look-alikes
| Look-alike | How to tell them apart |
|---|---|
| Southern fire ant (native) | Similar size and color, but less aggressive, with irregular nests of scattered soil and many obscure entrances.[1] |
| Harvester ants | Workers are all the same size and red.[1] |
| Black imported fire ant | The other imported fire ant species. APHIS describes imported fire ants as reddish brown or black, and Kentucky says the two species can hybridize.[7][2] |
Where it lives
Infests most of 11 southern states and Puerto Rico and arrived in Southern California in 1998; it is spreading into new areas such as southern Kentucky, often moved in soil, nursery stock, mulch or hay.[1][2]
Biology and life cycle
Colonies have one queen or many; multi-queen colonies bud into new mounds nearby and can reach very high densities. Kentucky says single-queen colonies are more territorial, and UC says multi-queen colonies sometimes approach 1,000 mounds per acre in southeastern pastures.[1][2]
New queens may fly 2 to 3 miles from the home colony after mating flights. Kentucky says mating flights can happen when it is 70 to 95°F and may be more likely after rain.[2]
After mating, queens shed their wings, seal themselves into a small hole in the soil and begin laying eggs, and the first small workers develop in about one month. In California, reproductives are produced all year, most of them in spring.[1]
They feed on almost any plant or animal material, including insects, ticks, seedlings, plant buds, fruits and seeds. Kentucky notes they also prey on pest caterpillars, fleas and ticks.[1][2]
Fire ants spread naturally, including floating as rafts during floods, and are moved in soil, nursery plants, mulch, hay and earth-moving equipment. Kentucky reported new infestations in McCreary, Whitley and Knox counties in 2022.[2][7]
Damage and signs
Health risk
Fire ants grip the skin with their jaws, then bite and sting. CDC/NIOSH says the venom causes a burning sensation and red bumps that turn into white, fluid-filled pustules within a day or two. People who are allergic to the venom can have anaphylaxis, a severe and potentially life-threatening reaction that needs emergency care.[5][6]
Control
Prevention
Teach children and visitors to avoid mounds. CDC/NIOSH advises not standing on or near mounds, looking over an area before working in it, and taking care when lifting things off the ground, which may be covered in ants.[1][5]
Pesticides
Fire ant baits are the recommended approach: workers carry bait back to the colony. Apply when ants are actively foraging (about 70 to 90°F), on dry ground with no rain or irrigation expected, using fresh bait. UC adds that baits lose strength quickly in heat, water and sunlight, and an opened package may stay fresh for only a couple of weeks.[1][2]
Spraying foraging ants won't control the colony, and disturbing or spraying a mound can make it move and spread.[1]
Sources differ on mound treatments. UC IPM does not recommend mound treatments or broadcast granules that aren't fire ant baits, saying they mostly kill foraging workers and that pyrethroids from such products have been found in urban creeks at levels toxic to aquatic life. Texas A&M's Two-Step and Kentucky include labeled mound drenches, dusts and granules for individual problem mounds.[1][3][2]
When to call a professional
In areas where fire ants are new, report suspected mounds to the state agriculture department or extension office instead of treating them yourself; licensed professionals have the most effective products. APHIS quarantines regulate moving hay, soil, plants and soil-moving equipment out of infested areas.[1][2][7]
The Texas A&M Two-Step Method
For yards with five or more mounds per quarter acre, Texas A&M AgriLife recommends the Two-Step Method: broadcast a fire ant bait over the whole yard, sometime between late August and mid-October (baits can be applied any time in the warm season), then treat individual problem mounds.[3]
Baits are slow: they take weeks to months to reach 80 to 90 percent control. Use fresh bait, apply with a hand-held seed spreader when the ground is dry, no rain is expected for 24 to 48 hours and ants are foraging (test by placing a little bait by a mound and checking within 30 minutes), and reapply once or twice a year.[3]
For step two, use a mound drench, granule, bait or dust labeled for fire ants. Pouring 2 to 3 gallons of very hot water on a mound kills the colony only about 60 percent of the time and kills the surrounding grass.[3]
If fire ants sting you
Move away from the mound and rub the ants off briskly; CDC/NIOSH says they hold on to the skin with their jaws.[5]
Wash the area with soap and water. MedlinePlus suggests ice wrapped in a washcloth, 10 minutes on and 10 minutes off, repeated, and an antihistamine or anti-itch cream if needed. CDC/NIOSH says antihistamines may help but can cause drowsiness; follow the package directions.[6][5]
Over the next several days, watch for signs of infection, such as increasing redness, swelling or pain.[6]
Call 911 or get emergency care right away for severe chest pain, nausea, severe sweating, trouble breathing or wheezing, serious swelling, swelling of the face or mouth, throat tightness or slurred speech. If the person carries an epinephrine auto-injector, help them use it.[5][6]
NIOSH says people with a history of severe allergic reactions to insect stings should carry an epinephrine auto-injector and wear a medical ID, and MedlinePlus says anyone who has had a severe, bodywide reaction to a bee sting should be referred to an allergist.[5][6]
Common questions
- Should I pour something on the mound?
- UC IPM advises against disturbing or spraying mounds on their own because the colony can move; Texas A&M's Two-Step pairs a yard-wide bait with treatment of individual problem mounds using labeled products. Texas A&M says pouring 2 to 3 gallons of very hot water on a mound kills the ants only about 60 percent of the time and kills the grass around it.[1][3]
- What should I do if fire ants sting me?
- Rub the ants off, wash with soap and water, use ice wrapped in a cloth and an antihistamine if needed, and watch for infection over the next several days. Call 911 for chest pain, trouble breathing, swelling of the face or throat, or slurred speech.[5][6]
- Are fire ants in my state?
- APHIS lists imported fire ants in Alabama, Arkansas, California, Florida, Georgia, Louisiana, Mississippi, North Carolina, Oklahoma, South Carolina, Tennessee, Texas, Virginia and Puerto Rico, and Kentucky found new infestations in 2022. In areas where they are new, report suspected mounds rather than treating them yourself.[7][2][1]
Sources
- University of California Statewide IPM Program, “Pest Notes: Red Imported Fire Ant, Publication 7487 (December 2013).” ipm.ucanr.edu/legacy_assets/PDF/PESTNOTES/pnredimportedfireant.pdf (accessed 2026-11-11)
- University of Kentucky Entomology, “ENTFACT-469: Imported Fire Ants in Kentucky.” entomology.mgcafe.uky.edu/ef469 (accessed 2026-11-11)
- Texas A&M AgriLife Extension Fire Ant Project, “Two-Step Method.” fireant.tamu.edu/controlmethods/twostep/ (accessed 2026-11-11)
- iNaturalist, “Solenopsis invicta taxon page (order and family).” www.inaturalist.org/taxa/67598 (accessed 2026-11-11)
- CDC, National Institute for Occupational Safety and Health (NIOSH), “Insects and Scorpions at Work.” www.cdc.gov/niosh/outdoor-workers/about/insects-and-scorpions.html (accessed 2026-11-11)
- MedlinePlus, U.S. National Library of Medicine, “Insect bites and stings (Medical Encyclopedia).” medlineplus.gov/ency/article/000033.htm (accessed 2026-11-11)
- USDA Animal and Plant Health Inspection Service, “Imported Fire Ants.” www.aphis.usda.gov/plant-pests-diseases/ifa (accessed 2026-11-11)