Red Imported Fire Ant

Polymorphic workers ranging from 1.6 to 6 mm in a single colony, reddish-brown with a darker abdomen, two petiole nodes, a ten-segmented antenna with a two-segmented club, and a prominent stinger. Mounds are dome-shaped, fluffy, and have no central entry hole, workers enter through subsurface tunnels. Disturbing the mound triggers a fast, aggressive swarming response with thousands of workers boiling to the surface, the single most reliable field test against the look-alike native fire ants (S. xyloni, S. geminata).

Colonies may be monogyne (one queen, territorial, ~150–200 mounds per acre) or polygyne (many queens, non-territorial, 400–800+ mounds per acre). Mature colonies hold 100,000–250,000 workers, mate in flight after warm rains, and disperse new queens up to a mile. Floods trigger floating 'rafts' of interlocked workers carrying the queen and brood to new ground, which is one of the most effective dispersal behaviors of any pest ant.

Medically important: stings cause pustules, secondary infection, and anaphylaxis in sensitized individuals; multiple fatalities per year in the U.S. Damages electrical equipment (HVAC, traffic signals, well pumps, irrigation controllers) where workers chew insulation and short contacts. Suppresses native ground-nesting wildlife, displaces beneficial arthropods, and injures livestock, pets, and ground-nesting birds. Federally regulated: nursery stock, sod, hay, and soil-moving equipment from quarantine counties require certification.

Texas A&M's 'Two-Step Method' is the operational standard for residential and turf settings. Step 1: broadcast a fire-ant bait over the entire property in late spring and early fall when soil temperatures are 70–95°F and ants are actively foraging (test with a potato chip). Step 2: treat individual problem mounds 7–10 days later with a contact mound treatment. Avoid disturbing mounds before bait uptake. In large pastures or sensitive sites use IGR-based baits (methoprene, pyriproxyfen) for slow but durable suppression; in commercial sites combine fast-acting metabolic baits with non-repellent perimeter sprays.

Product names are representative of the active-ingredient class and intended for licensed PMPs. Always read and follow the label; rates, sites, and restrictions vary by formulation and state registration.