Fire ants, known for their aggressive nature and painful stings, are a concern across the United States. While not native to California, these invasive pests have established populations in certain areas, prompting efforts to manage their spread and impact.
Fire Ant Status in California
The red imported fire ant (Solenopsis invicta) officially arrived in California in 1998, initially detected in residential and commercial areas across Orange, Los Angeles, Riverside, and San Bernardino counties. Infestations were also found in almond groves in the Central Valley, likely introduced through honey bee hives from Texas. This species, native to South America, has since spread to other parts of southern California, including the Coachella Valley, and sporadically into San Diego, Santa Barbara, Sacramento, Madera, Merced, and Stanislaus counties. The movement of infested soil and container plants has been a primary means of their spread to new, uninfested locations.
Spotting Fire Ants
Red imported fire ants are identifiable by their reddish-brown bodies and darker abdomens, with workers varying in size from about 2.4 to 6.0 mm. Unlike many other ant species, their colonies contain workers of different sizes. A key physical characteristic is their two-segmented waist (petiole) and 10-segmented antennae with a two-segment club.
Their nests are distinctive, often appearing as dome-shaped mounds of loose, crumbly soil, typically without a visible central entrance hole. These mounds can reach up to 30 cm high in undisturbed areas, though in irrigated turf, they might be flatter and resemble gopher mounds. When disturbed, these ants exhibit aggressive behavior, swarming quickly and stinging anything touching their mound. The sting causes immediate burning pain, followed by itchy red welts that develop into pus-filled blisters (pustules) within 24 hours, a nearly diagnostic symptom.
Impacts of Fire Ants
For humans and pets, while most reactions are localized, some individuals may experience severe allergic reactions, including anaphylaxis, which can be life-threatening. Multiple stings can also lead to systemic symptoms like vomiting, diarrhea, and shortness of breath.
Beyond health impacts, fire ants cause significant damage to agriculture and infrastructure. In agricultural settings, they can damage crops such as soybeans, corn, and eggplant, and infest almond and citrus groves. Their mounds can interfere with farm machinery and irrigation systems, leading to equipment damage. They also pose a threat to electrical equipment, nesting in control boxes and chewing through wires, which can cause short circuits and malfunctions. Fire ants can also outcompete native ant species and prey on other wildlife, affecting local ecosystems.
Addressing Fire Ant Issues
If you suspect a fire ant infestation on your property, do not disturb the mound or attempt to treat it yourself. The California Department of Food and Agriculture (CDFA) has established a toll-free hotline (1-888-4FIREANT or 1-888-434-7326) for reporting suspected fire ant sightings. The hotline is available 24/7, with operators assisting during business hours.
California has an ongoing program focused on eradicating red imported fire ants within the state. State personnel will identify the ants and, if confirmed, may provide approved treatments at no cost or recommend appropriate actions. In areas where fire ants are established and eradication programs are not in place, management involves using fire ant baits, which worker ants carry back to the colony to eliminate the queen and the entire nest. Professional pest control services are often recommended, as they have access to effective products and expertise in managing these pests.