Most ants in San Diego County, including the common Argentine ant do not harm people and usually only have to be controlled when they enter homes. This is not the case with the red imported fire ant (Solenopsis invicta), a new invasive species in Southern California. These ants quickly climb on any person or animal when their nest or a food source is disturbed, and inflict painful bites and stings. White pustules that form at wound sites take several weeks to disappear, and may become infected or leave permanent scarring. People who have a severe allergic reaction to the venom can suffer anaphylactic shock and may die without prompt medical attention.
Red imported fire ants are a dark reddish-brown color. The workers in a colony are variable in size ranging from 1/16 to 1/5 inch in length. The ants usually live in lawns and other moist, irrigated areas where they build dome-shaped mounds of loose, crumbly soil up to 18 inches across. Our native southern fire ant (Solenopsis xyloni) and harvester ants (Pogonomyrmex californicus), also called red ants, tend to nest in drier, un-irrigated areas. These ants also bite and sting but they are much less aggressive than red imported fire ants.
Red imported fire ants and southern fire ants are similar in appearance. Harvester ants are all the same size, 1/5 inch long. If you don’t know what type of ant you have in your yard, you can obtain help with identification by calling a statewide toll-free number 1-888-4FIREANT, or 1-888-434-7326. In San Diego County call the San Diego County Department of Agriculture at 858-694-2739 to report a possible infestation.
Hiring a licensed pest control operator is recommended if you have red imported fire ants. Pest control professionals have access to the most effective management products and experience controlling fire ants. Local pest control companies can be found online and in the telephone yellow pages under pest control
The most effective way to control fire ants is with toxic bait which foraging ants take back to their nest and share with the entire colony. Some bait products labeled for fire ant control can be purchased at home improvement stores and garden centers. If you use one of these products, carefully read and follow directions on the label. Spraying foraging ants with insecticide will not eradicate a colony. Spraying a nest of red imported fire ants may cause the ants to disperse and make control more difficult.
For more information on ants see
UC Pest Note #7487 “Red Imported Fire Ant”: http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7487.html
UC Pest Note #7411 “Ants”: http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7411.html
and UC Pest Note #7416 “Carpenter Ants” http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7416.html
By V. Lazaneo, Urban Horticulture Advisor, Emeritus, UC Cooperative Extension, October 2012