How to Manage Pests
UC Pest Management Guidelines
Red Imported Fire Ant
Scientific names: Solenopsis invicta
(Reviewed 8/17, updated 8/17)
In this Guideline:
Description of the pest
Red imported fire ant is an invasive species that is not currently present in California almond orchards. However, growers should be aware of this pest and watch for it, particularly after bloom in orchards that rented bee hives from areas of the country that are known to be infested.
Fire ants are characterized by having a 2-segmented petiole (the narrow waist between the thorax and abdomen), 10-segmented antennae with a 2-segment club, and a stinger. There are two native fire ant species likely to be encountered in California that can be confused with the red imported fire ant. The more common one, the southern fire ant (Solenopsis xyloni) is 0.1 to 0.18 inches (2.5 to 4.5 mm) in length and found in coastal and inland regions. It is very similar in appearance to the red imported fire ant. The southern fire ant differs from the red imported fire ant in that it is bicolored, with a reddish head and thorax and a dark brown abdomen. By contrast, the red imported fire ant is an almost uniform dark reddish-brown and 0.12 to 0.24 inches (3 to 6 mm) long. Both species have workers of mixed sizes.
Red imported fire ant mounds are frequently built up into domes, while the southern fire ant mounds are irregular craters. Mounds produced by red imported fire ants can reach 10 to 12 inches in height: however the size of mounds will vary with soil types, and mounds may be absent. A characteristic difference between these species is the aggressiveness of the workers. Although they will both sting, the ferocity of the red imported fire ant is notable. Any object touching their mound is immediately attacked and stung, and the workers will quickly run up a stick that touches the mound. It is still uncertain whether the red imported fire ant colonies in California have one or multiple queens per colony. This could have a significant impact on the selection of treatment strategies.
Red imported fire ants can chew on soft plant tissue and growing buds. Their stinging behavior can be hazardous to people and pets. Their sting is noxious and produces a pustule on the skin that can scar if it gets infected. They can clog irrigation lines and short-circuit electrical systems.
Although red imported fire ants are not present in all areas of California, they are a serious pest and are subject to quarantine regulations. In Southern California, state and federal officials have placed Orange County and portions of Los Angeles County and Riverside County under quarantine that limits the movement of regulated items including plants and soil. The California Department of Food and Agriculture (CDFA) has established the Red Imported Fire Ant hotline (1-888-4FIREANT or 1-888-434-7326) to report any suspected occurrence of red imported fire ant in California. This hotline is available 24 hours a day, 7 days a week to provide current information on the red imported fire ant. An operator is available Monday through Friday, 8:00 a.m. to 8:00 p.m.; after hours, callers may leave a message. All calls reporting suspected red imported fire ant mounds will be answered and the information will be referred to the appropriate agency for response. Border programs exist to ensure that red imported fire ants do not hitchhike on beehives brought into California for almond pollination.
There are no commercial biological control agents presently available. The U.S. Department of Agriculture and the University of Texas have begun the first biological control program to control fire ants using a tiny South American fly, called a phorid, which is a natural parasite of fire ants. These flies are being mass-reared and released in Florida and Texas for evaluation. Researchers are also investigating other parasitic insects and even protozoa from South America.
If you suspect a colony is red imported fire ant, use four or five small plastic vials baited with Spam meat as monitoring stations placed at 50-foot intervals around the colony. The sample should then be sent to your nearest cooperative extension advisor for identification.
In areas not known to have red imported fire ant, contact CDFA or your county agricultural commissioner's office for information on approved treatments. RIFA Hotline: 1-888-4FIREANT (1-888-434-7326). In areas with established red imported fire ant populations where there are no eradication programs in place, see treatment guidelines for ants.
UC IPM Pest Management Guidelines:
Insects and Mites
F. G. Zalom, Entomology, UC Davis
Acknowledgment for contributions to Insects and Mites:C. Pickel, UC IPM Program, UC Cooperative Extension, Sutter and Yuba counties
W. J. Bentley, UC IPM Program, Kearney Agricultural Center, Parlier
R. A. Van Steenwyk, Insect Biology, UC Berkeley
R. E. Rice, Kearney Agricultural Center, Parlier
L. C. Hendricks, UC Cooperative Extension, Merced County
R. L. Coviello, UC Cooperative Extension, Fresno County
M. W. Freeman, UC Cooperative Extension, Fresno County