By Vincent Lazaneo.
As discussed in the previous installment of this column, a new invasive pest, the red imported fire ant (RIFA), is rapidly colonizing California. The dangerous and destructive ant now infests most of Southern California and colonies have been detected at several locations in the City of San Diego and Poway.
Left: Recognizing RIFA mounds may help homeowners avert possible harm to children, pets, and plants. Image courtesy of Insects Unlocked.
RIFA can build nests in lawns and other irrigated plantings, under adjacent pavement, in outdoor electrical and utility boxes, near buildings, and in the walls of homes. Colonies aggressively defend their nest mounds (spanning two inches to more than eighteen inches across), which resemble gopher mounds, but have much finer soil. The small (1/16" to 1/5” long), dark reddish-brown ants rapidly sting any person or animal multiple times when a colony is disturbed. Their stings are very painful and for a few people the venom can cause an allergic reaction that may be life threatening.
RIFA colonies also pose a threat to domestic and native animals. They can attack and kill confined pets, young livestock, poultry, and native wildlife—especially young birds in nests and ground dwelling animals such as lizards.
RIFA can feed on almost any plant or animal material. It feeds on a variety of food products, including sweets, grains, meats, butter, cheese, nuts, grease, and jellies and jams. Outdoors, RIFA feeds on the leaves, stems, and roots of agricultural crops, and damages lawns and ornamental plants. The ants feed on germinating seeds, young seedlings, plant buds, bark on young trees, and developing fruit and seeds. RIFA attacks other insects and disrupts biological control when it kills beneficial insects that help combat plant pests. The ants may also clog irrigation lines and can short circuit outdoor equipment such as irrigation controllers and pool pumps.
RIFA nests should be treated with a granular bait labeled for fire ants to safely eliminate the entire colony. In some areas, including San Diego and Los Angeles, this service is currently provided by the County Agricultural Commissioner’s Office (call 1-800-200-2337 in San Diego); the local vector control district provides this service in other jurisdictions (including Orange County and Coachella Valley).
Do It Yourself
Homeowners who want to treat a RIFA colony should use a granular bait labeled for fire ants containing hydramethylnon, such as Amdro®. This bait is sold at some retail outlets and a six-ounce container can be ordered online through Amazon. Only a small amount of bait is needed and fresh bait from an unopened container works best. The bait only remains fresh for about two weeks after a container has been opened.
Always read the entire label before you open the bait and carefully follow the directions. Fire ant bait is scattered lightly (about twenty granules per square foot) over an area when ants are foraging on the ground (day or night depending on temperature). To find out if RIFA are active, put out small pieces of greasy food such as potato chips or spam and check for ants in about thirty minutes. Apply bait on dry ground and wait at least two hours after irrigating turf. Never apply bait in piles or scatter it on pavement where it could be washed into a storm drain.
Vincent Lazaneo is UC Urban Horticulture Advisor Emeritus. He has a master’s degree in horticulture and a teaching credential in vocational agriculture from UC Davis. In 1983, Vince began the Master Gardener program in San Diego. Vince frequently contributes, or has contributed to, the San Diego Union-Tribune, Mira Mesa Living, and other publications. He enjoys growing specialty plants in his home garden, reading, hiking, and fishing.