Red Imported Fire Ant (Solenopsis invicta)

Identification

Red imported fire ants are small — workers range from 1/16 to 3/16 inch, and a single colony contains multiple worker sizes (polymorphic). Color is reddish-brown to dark brown. They are hard to tell from native ants by sight alone, so the reliable test is behavioral. Disturb a mound and fire ants boil out aggressively, running up anything that touches it and stinging again and again. Carpenter ants, by contrast, scatter. Native ants scatter; fire ants attack.

Fire ant mounds are dome-shaped soil structures with no visible entrance hole on top — workers enter and exit through underground tunnels. Mounds can reach 18 inches tall and 24 inches across in established colonies, though many active mounds are smaller and less conspicuous.

Colony Behavior in the Rio Grande Valley

Fire ant colonies in Cameron and Hidalgo counties are active 365 days a year. Brownsville — and agricultural communities like Weslaco surrounded by irrigated groves — never gets the sustained hard freezes that kill fire ant queens in northern states. A mature colony contains 200,000–500,000 workers and can have multiple queens (polygyne form), making eradication of individual colonies through mound treatment extremely difficult without broadcast bait.

After rain, mounds rebuild within hours. After flooding, common during hurricane season, entire colonies raft on the water surface as a living mat, floating until they contact dry ground and re-establishing immediately. This behavior explains why fire ants survive every flood event the Valley throws at them.

Sting Reaction

Fire ant stings produce an immediate burning pain followed by a raised red welt. Within 24 hours, a characteristic white pustule forms at each sting site — this is a sterile pustule (not infection) caused by the venom. Multiple stings are typical because fire ants grip with their mandibles and sting repeatedly in a circular pattern. For 1–2% of the population, fire ant stings trigger systemic anaphylaxis requiring emergency medical treatment.

Why Professional Treatment Works

Home remedies, boiling water, gasoline, baking soda, grits, either kill only surface workers (the queen survives underground) or are dangerous to apply. Professional broadcast bait distributed across the entire yard is carried underground by foraging workers and shared with the queen through the colony's food-exchange system (trophallaxis). This kills the queen and collapses the colony from the inside — the only method that produces lasting results.