Red Imported Fire Ant

RED IMPORTED FIRE ANT Integrated Pest Management for Home Gardeners and Landscape Professionals Although the red imported fire ant fire ant, for instance, are usually irreg- two nodes (Solenopsis invicta) is common in 12 ular and consist of scattered soil with southern states, it is new to California multiple obscure entrances. Unlike and has recently been found infesting the other ant species mentioned, red numerous residential and commercial imported fire ants tend to build nests areas in Orange, Los Angeles, River- stinger in open, sunlit, grassy areas that are mandible side, San Bernardino, and to a lesser ten-segmented typically irrigated. They will readily antenna extent, San Diego counties. The spread of these ants has largely been a result run up any object that touches their mound, whereas the other species Figure 1. Adult red imported fire ant of the movement of infested soil to worker. uninfested areas. are much less aggressive. Because red imported fire ants often build their LIFE CYCLE IDENTIFICATION nests in turfgrass areas in California, The fire ant life cycle, like that of other Red imported fire ant workers (Fig. 1) frequently the mounds have been social Hymenoptera (ants, bees, and 1 1 are variable in size ( ⁄16 to ⁄ 5 inch long) mowed and are nearly flat, appearing wasps), consists of four main stages: and dark reddish brown. Unlike our as soft, loose dirt that obscures the egg, larva, pupa, and adult (Fig. 3). The native southern fire ant (Solenopsis grass and looks like a bald spot in the egg, larval, and pupal stages occur xyloni) and harvester ant (Pogonomyr- turf. within the underground nest and are mex californicus), the red imported only seen when nests are disturbed or fire ant can quickly produce many In some instances red imported fire when they are being carried to a dif- nests and colonize a yard. Harvester 1 ants do not build mounds but nest ferent location by workers. The eggs ant workers are all the same size ( ⁄ 5 inch long) and are red in color. Many in places such as rotten logs, walls of are almost too small to be seen with people refer to these as “red ants.” buildings, or under sidewalks. the unaided eye. They hatch into the The most common ant around homes mound in California is the Argentine ant, Linepithema humile, a small grayish 1 black ant that is uniform in size ( ⁄10 foraging tunnel nest chamber inch long) and is seen moving along in long trails. While there are several physical characteristics that distinguish red imported fire ants from other common ant species found in California, one way to recognize this pest is to observe its aggressive behav- ior when its nest or food source is disturbed or to experience its painful bite and sting. In areas that are not disturbed, red tunnels to water table imported fire ants typically make tunnels to water table dome-shaped mounds (Fig. 2) that are about 18 inches across and about 8 to 12 inches tall. They resemble large gopher mounds or look like crumbly earth with small holes; these mounds readily distinguish red imported fire ant colonies from other California ant colonies. Nests of the native southern Figure 2. Cross section of a red imported fire ant mound. PEST NOTES Publication 7487 University of California Agriculture and Natural Resources July 2007 July 2007 Red Imported Fire Ant DAMAGE adult worker The red imported fire ant’s sting is a (all are females) serious concern to people and their pets. Venom injected into the skin causes a burning sensation (hence the name “fire adult ant”). Both southern fire ants and red queen imported fire ants become very agitated when their nests are disturbed, but red imported fire ants are much more aggressive and can quickly climb onto the object or person causing the distur- bance and begin stinging. A single red imported fire ant can bite and sting its victim repeatedly (Fig. 4). Symptoms start as a burning and itching sensation followed by the formation of a white pustule, which takes several weeks to pupa disappear. The pustules can become eggs infected if not kept clean and may leave permanent scarring. A small percentage of the human popu- larva lation is allergic to these stings. If a person experiences chest pains, nausea, Figure 3. Life cycle of the ant. dizziness, or shock, they should seek emergency medical assistance imme- grublike larvae that are fed by the color and have a smaller head and diately after a stinging incident. Avoid workers. There are four larval instars larger thorax than female reproduc- medical emergencies by teaching chil- (stages); the fourth larval instar is par- tives. During a mating flight, the dren and visitors about fire ants. ticularly important because it is the winged males and females fly and only stage that can ingest solid food. mate in midair before falling back to Fire ants feed on almost any plant or Once the larvae finish their growth, the ground. Males die shortly after- animal material, including other insects, they molt into pupae, which look like ward; the mated queens remove their ticks, ground-nesting animals, young adults except that their legs and anten- wings and dig a small hole in the soil trees, seedlings, plant buds, developing nae are held tightly against the body. fruits, and seeds. In addition to their These pupae are initially white, but and seal themselves inside. In the stings, the red imported fire ant causes begin to turn darker as they mature. nest, the queens begin to lay eggs that problems by building its nests around In the final molt the pupa becomes an develop into small worker ants in a trees, yard plants, pipes, and in the adult. month or two. walls of structures. Colony-building Most larvae develop into sterile worker Some fire ant colonies have only one can damage plants, lawns, and outdoor ants, all of them female and wingless. queen per nest and are called “mono- electrical fixtures. However, some larvae in the colony gyne” colonies. Others can have many receive extra food during their devel- queens and are called “polygyne” opment and become much larger than colonies. The polygyne colony may be the larvae destined to become work- more difficult to control because all the ers. These larger larvae will develop queens must be killed to prevent the into reproductives. Large numbers of colony from surviving. Polygyne colo- reproductives are normally produced nies frequently expand by “budding”; once a year in the spring in prepara- tion for a mating flight, although flights i.e., some of the queens and workers can occur more than once a year if start a new mound nearby. This pro- conditions are favorable. The female cess accounts for much higher mound reproductives are future queens and densities for polygyne colonies than have wings. Male larvae develop into for monogyne colonies, sometimes Figure 4. A red imported fire ant attack winged adult males that are black in approaching 1,000 mounds per acre. involves both a bite and a sting. ◆ 2 of 4 ◆ July 2007 Red Imported Fire Ant MANAGEMENT the Vector Control Districts have active the rest of the colony. Most fire ant baits Because fire ants can sting en masse, fire ant eradication programs and will consist of a matrix of de-gelled corn most people will want to keep them assist residents with treatment. In Los grits that are coated with soybean oil off their property. This contrasts with Angeles County, the county agricul- containing the toxicant. Baits should be other common ant species, such as the tural commissioner may provide treat- put out when ants are seen walking on Argentine ant, where the primary goal ment in some areas. In other areas and the ground (temperatures from 70° to is to keep them out of homes. For man- in Riverside County, residents may be 90°F are best). In hotter weather, baits agement of household ants, see Pest responsible for their own treatment. are best applied in the evening. They Notes: Ants, listed in References. Hiring a licensed pest control opera- will then forage overnight on the bait. tor is strongly recommended because Baits lose their effectiveness quickly The red imported fire ant is a quaran- licensed professionals have access to with extreme heat, water, and sunlight. tined pest in California. If you suspect the most effective management prod- Fresh bait from an unopened container that the pest is on your property you ucts and experience in controlling this works best; an opened package may can call a statewide toll free number pest. remain fresh for only a couple of weeks. that has been set up by the California Furthermore, the ground should be dry Department of Food and Agriculture For professionals and residents car- to avoid further deterioration of the (CDFA) (1-888-4fireant or 1-888-434- rying out their own management baits. On watered turf, in most cases 7326) to help get the pest identified by programs, ant baits are recommended a couple of hours without irrigation someone in your area. There is also an because they are inexpensive, highly should be sufficient to allow the ants informative Web site, http://www.fire- effective, and safe for the environment. to take the baits to their nests Also, do ant.ca.gov. If you are in an area where Table 1 shows many bait products not apply baits if rain is expected. Fire the fire ant has not been previously labeled for use against fire ants in Cali- ant baits are broadcast at 1.5 lbs per established, contact CDFA for help and fornia.

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