Battling Imported Fire Ants: Identification, Control, and Emerging Solutions

(Editor's Note: Originally published April 12, 2008. Comments welcome; authors may not respond promptly.)

Red imported fire ants (Solenopsis invicta) are incredibly aggressive. Disturb a mound and you're under attack. The FDA estimates $5+ billion annually in medical, damage, and control costs; $750 million in agricultural damage. Native to Brazil, they arrived in Mobile, Alabama via cargo ship in the 1930s and spread across the Southern and Southeastern U.S.

After heavy rains, mounds surface as workers move temperature-sensitive brood up. In dry conditions, they move deeper—mounds may be invisible but ants remain. Mounds extend up to four feet underground.

Fire ants bite to grip, then sting repeatedly—like a cigarette burn. Each sting forms an itchy, painful pustule. Hydrocortisone or Listerine may soothe. Severe allergic reactions (swelling, breathing difficulty) require immediate medical attention.

Control Strategies

Assess the problem: Widespread infestation? Broadcast fire ant bait with a spreader in dry weather (several dry days forecast).

Best bait: Spinosad (sometimes sold as 'Conserve')—a natural biological control originally for caterpillars, highly effective on fire ants. Safe for plants, pets, people. Available as granules or liquid. 16 oz covers 22 mounds or 10,000 sq ft. Use 4 tbsp per mound or ¾ cup per 1,000 sq ft broadcast.

Apply directly on and around mounds—workers carry bait to the queen. Her death dooms the colony. Takes ~6 weeks. Follow with orange oil drench (the "Texas Two-Step"). Boiling water kills surface ants but rarely reaches queens and destroys grass.

Ignore folk remedies: Grits, rice, aspartame, oatmeal don't work—colonies may move but survive.

Biological Hope: Phorid Flies

Scientists are developing Pseudacteon phorid flies—parasitoids that lay eggs in fire ants. Larvae consume the ant's head, which falls off as the adult fly emerges. Tallegeda County, AL and parts of Texas already have established populations. While not a silver bullet, it's a promising step.

Visit the Texas Imported Fire Ant Research and Management Project for more.