California's Blight

Ants are also very important structural pests. In the western United States, they are considered the No. 1 pest, ahead of cockroaches and spiders, which are reported as No. 2 and No. 3, respectively. A recent survey conducted by Pest Control Technology/Service Technician magazines reported that ants were considered the No. 1 perimeter pest by 47.8% of respondents. Edward O. Wilson, the world’s foremost myremecologist (ant specialist), attested to the international importance of ants as structural pests when he stated that the question most often asked of him is “What do I do about the ants in my kitchen?”

In Southern California, ants account for a significant portion of revenues generated by structural pest control operators, and the Argentine ant is the No. 1 structural pest ant. It is the most persistent and troublesome of all of the house-infesting ants in this area. The Argentine ant is also established across the southeastern states, and localized infestations have been found in Hawaii, Nevada, Arizona, Missouri, Maryland, Oregon, Washington, Illinois and Michigan. They are commonly found in some extremely harsh environments in the West and Southwest where they could not survive without moisture provided by man. Examples of these arid areas are Palm Springs, Calif., Las Vegas and Phoenix.

Although it is especially fond of sweets, the Argentine ant will seek out almost every type of food. It is an ant that thrives in the urban environment where moisture, one of its fundamental requirements, is provided liberally via irrigation of lawns and other landscaped areas. Excessive irrigation often results in lush vegetation which supports high populations of honeydew-producing insects. Honeydew is the primary food of Argentine ants in Southern California. It is a highly preferred food for Argentine ants because it provides them with carbohydrates and water — two of their major requirements for survival, especially in arid environments.

With almost all of its requisites continuously supplied by man, it is no wonder that the Argentine ant dominates the environment around structures in Southern California. This fiercely competitive species is capable of displacing native ant species. It has extirpated (caused localized extinction) and in some cases exterminated other species of ants, including several native species.

Controlling this ant is especially difficult. In Southern California, bait products have proved to be of little help, and in fact the key to controlling the Argentine ant here is to find and destroy its nests. This too is extremely difficult, because Argentine ant nests have been found in some very unlikely places.

UNUSUAL ARGENTINE ANT INFESTATIONS. During 20 years of applied structural myrmecology work in Southern California, Nevada and Arizona, I have encountered numerous Argentine ant populations in some of the most unusual situations in and around structures. A list of some of the most unusual problems which I have encountered with Argentine ants in Southern California is presented here. These situations are described to assist structural PCOs in their efforts to locate and treat Argentine ant nests and to obtain control of this ant in and around structures. Most of the situations described here are the result of actual experiences in the field.

1. Empty soda cans held indoors for recycling purposes have often been responsible for causing infestations of Argentine ants within structures. Also, people collecting soda cans for recycling along streets, roads, highways, freeways, parking lots, etc. have often found themselves attacked by Argentine ants which were infesting the cans. Trash receptacles within structures, even those in high rise office buildings, often serve as magnets for Argentine ants, especially if they contain soda cans and scraps of human food.

2. Argentine ants protect and tend honeydew-producing Homopterous insects (such as aphids, mealybugs, whiteflies and scale insects) in such an aggressive manner that they prevent natural enemies (such as ladybird beetles or parasitic wasps) from exercising any appreciable control over these pestiferous insect populations.

Argentine ants are commonly found tending Homopterous insects in backyard fruit trees in such large numbers that they make the harvesting of fruits an unpleasant experience. They will also infest hummingbird feeders as well as honeybee colonies.

3. Argentine ants are capable of carrying pathogenic bacteria in hospitals and food handling establishments (Ipinza-Regla et al. 1981, 1984). It can be assumed that this ant is also capable of transmitting disease organisms in convalescent homes, urgent care centers, dental offices and anywhere food is prepared, handled, processed, sold or displayed for sale. During the course of investigating outbreaks of Listeriosis associated with cheese in California, scientists with the Food and Drug Administration recovered Listeria monocytogenes from Argentine ants which were present in cheese manufacturing facilities (Gorham 1991). Argentine ants were also found in sterile surgical kits in storage at a medical facility.

4. Male swarmers of Argentine ants are often attracted in large numbers to outdoor lights, particularly mercury vapor lamps. Many of these ants inadvertently enter structures via cracks, crevices, gaps and other points of entry around doors and windows. In one situation, an unusual problem resulted when numerous male Argentine ant swarmers were attracted to a mercury vapor lamp adjacent to a swimming pool. Large numbers of ants fell into the pool forming floating rafts. These “ant rafts” eventually clogged the pool’s filtering system. In another case, Argentine ants were found at several locations in the joint between the walls of an in-ground swimming pool and the overhanging tip of the pool. Male alates of Argentine ants do not resemble typical worker ants, and PCOs often misidentify these winged ants as midges or gnats because they are not familiar with male Argentine ants.

5. Researchers Suarez and Chase (1997) reported that the Argentine ant is forcing a dramatic change in the diet of the horned lizard, a species of special concern in Southern California. Populations of this lizard have been declining in this area for some time now. In its natural habitat, the horned lizard feeds almost exclusively on native harvester ants. In areas where harvester ants have been displaced by the Argentine ant, horned lizards are forced to feed mainly on beetles. Suarez and Chase claim that this dietary change is likely contributing to the lizard’s decline. This type of cryptic effect by exotic species in new ecosystems often goes unnoticed.

6. Argentine ant infestations have been found in buses, cars, trucks, trains, recreational vehicles, motor homes, mobile lunch vehicles and other forms of transportation. They will readily invade these modes of transportation when attractive food and water are present in them.

7. Argentine ants have been found nesting in soils of potted plants and they are often carried indoors this way. They are also often introduced into new geographic areas in nursery stock and sod.

8. An infestation of Argentine ants was found in a freshly cut Christmas tree which was placed in a mixture of water and 7-Up designed to prolong the tree’s freshness. The ants were accessing the tree via a limb which was touching a window sill and they were making their way down to the base of the tree where they were feeding on the water and 7-Up mixture.

9. An Argentine ant nest was found in accumulated wind-blown soil on the roof of a building adjacent to an air conditioning unit. This nest was accidentally discovered by a PCO while investigating a bird problem. He had repeatedly failed to control the ants in the building because he had assumed the Argentine ant is always a ground-nesting species.

10. Argentine ants were found in old, deteriorating wood shake roof shingles of a building. This area of the roof was heavily shaded by overhanging tree branches which helped to keep the shingles moist, and thus attractive to the ants.

In another situation, an infestation of Argentine ants indoors resulted from the ants ascending a power pole, trailing on a telephone line and descending into the building at the roof line.

11. In-ground subterranean termite bait stations are commonly infested with Argentine ants in Southern California. In some cases, as many as 70% of in-ground stations have been infested with this ant. This is a major deterrent to in-ground subterranean termite baiting programs in the Southern California area.

12. A bizarre incident involving Argentine ants occurred in 1993, in a Los Angeles County cemetary. A deceased person was taken to a cemetery for interment. When the cemetery workers attempted to lower the casket into the grave, they discovered that the casket was too large for the hole made in the ground. The deceased person was quite a large individual and apparently the workers were not informed that the casket was oversized. The casket was placed on the ground while interment personnel were trying to find a solution to the problem. It was claimed during subsequent litigation that the casket and bouquets of flowers were on the ground for two hours before it was decided that they had to remove the casket and flowers and return at a later date to bury the person in an appropriately prepared grave. From here on, this incident took a macabre turn. The family of the deceased could not locate a facility to store the casket over the weekend so they decided to leave the casket on a gurney in a nearby tool shed. They returned on Monday to properly inter the deceased.

Prior to interment at the new grave site, a relative of the deceased decided to open the casket for one last look and farewell before it was lowered into the grave. To their shock, horror, dismay and amazement, Argentine ants were found crawling around the inside of the casket. Someone videotaped the scene within the casket. A multi-million dollar lawsuit was filed. Lawyers for the defendants contended that the casket became infested with Argentine ants while it was in the tool shed adjacent to the mausoleum over the weekend. The plaintiff’s attorney claimed that the casket and/or flowers were infested with ants while on the ground for some two hours at the burial site. An expert who viewed the videotape testified at the trial that the ants in the casket appeared disoriented and confused, as they were wandering about aimlessly. He used this observation to conclude that the ants in the casket were a small contingent of workers which were disconnected from their colony when the casket was moved.

Inspections of the tool shed and surrounding areas at the mausoleum where the body was kept over the weekend did not reveal nests or trails of Argentine ants. However, inspections of the original burial site revealed pronounced trails of Argentine ants ascending and descending two large trees in proximity to the grave site. The plaintiff’s attorney argued that the casket and/or flowers placed on the ground at the original burial site became infested with Argentine ants at that location. A jury awarded the plaintiff a sum in the high six figures.

CONCLUSION. The Argentine ant is a persistent, pervasive and intrusive structural pest in most areas where it occurs. It is a polygynous (having many queens) and a polydomous (having many nests) species. Colonies are not antagonistic to one another, and they often coalesce to form super-colonies consisting of numerous queens and hundreds of thousands of workers. These large colonies forage over expansive territories and trails often extend well over 400 feet (Gulmahamad 1995). Queens are very prolific and each can lay more than 60 eggs per day (Vargo and Passera 1992).

Generation time from egg to adult averages about 50 days and adults live about 60 days. (Newell and Barber 1913).

The Argentine ant is a nomadic, opportunistic, tramp species with very aggressive foraging behavior. It will rapidly monopolize and exploit a newly discovered food source and it exemplifies the strategy of “the firstest with the mostest.” It can rapidly relocate a nest to escape unfavorable conditions or to capitalize on a food source. The Argentine ant lacks natural enemies in areas where it has been introduced and it is an exception to the universal statement made by the eminent myremecologist Auguste Forel that “the greatest enemies of ants are other ants, just as the greatest enemies of man are other men.” All of the above attributes have enabled the Argentine ant to become a widely distributed and extremely successful ant species.

The Argentine ant often nests and travels in very unusual places within structures (Gulmahamad 1996). In urban areas, these ants are often responsible for generating much stress, frustration, aggravation, etc. in pest management professionals who frequently fail to control these ants in structures after numerous attempts to do so (Gulmahamad 1997).

It is important for pest management professionals who conduct business in areas where the Argentine ant is prevalent to become familiar with the behavior and habits of this ant. Unlike other house-infesting species, the Argentine ant often displays very unusual behavioral characteristics. These behavioral patterns can frustrate even the most sophisticated pest management professional.

Hanif Gulmahamad is an urban entomologist with Terminix International, Los Angeles.

References

Crowell, K.L. 1968. Rates of competitive exclusion by the Argentine ant in Bermuda. Ecology 49:551-555.

Erickson, J.M. 1971. The displacement of native ant species by the introduced Argentine ant, Iridomyrmex humilis (Mayr). Psyche 78(4):257-266.

Gorham, R.J. 1991. Food pests as disease vectors. pp. 477-482. In: Gorham, R.J. (ed). Ecology and management of food-industry pests. FDA Technical Bulletin 4. Association of Official Analytical Chemists, Arlington, Va.

Gulmahamad, H. 1995. Argentine ant: The Ghenghis Khan of the ant world. Pest Management 14: 9-15.

Gulmahamad, H. 1996. Argentine ant control in Southern California. What have we learned? Pest Control 64(6):58-59,62,64.

Gulmahamad, H. 1997. Argentine ants find Southern California hard to resist. Pest Control 65(6):72-73,76.

Haney, P., P.A. Philips and R. Wagner, 1993. A key to most common and/or economically important ants of California with color photographs. Cooperative Extension, University of California, Division of Agriculture and Natural Resources. Leaflet No. 21433. 4pp.

Ipinza-Regla, J. G. Figueroa and J. Osorio. 1981. Iridomyrmex humilis “hormiga Argentina” como vector de infecciones intrahospitalarias. I.-Estudio bacteriolocigo. Folia Entomologica Mexicana 50:81-96.

Ipinza-Regla, J., G. Figueroa and I. Moreno. 1984. Iridomyrmex humilis (Formicidae) y su papel como posible vector de contaminacion microbiana en industrias de alimentos. Folia Entomologica Mexicana 62:111-124.

Newell, W. and T.C. Barber. 1913. The Argentine ant. U.S. Department of Agriculture Bureau of Entomology Bulletin 122:1-98.

Suarez, A. and T. Chase. 1997. Invasive Argentine ant is no picnic. Science News 152 (8/23/97), p. 116.

Vargo, E.L. and L. Passera. 1992. Gyne development in the Argentine ant, Iridomyrmex humilis: role of overwintering and queen control. Physiol. Entomol. 17:193-201.

Ward, P.S. 1987. Distribution of the introduced Argentine ant (Iridomyrmex humilis) in natural habitats of the lower Sacramento Valley and its effects on the indigenous ant fauna. Hilgardia 55(2):1-16.