The "Argentine Ants"

The most common ant in southern California is the Argentine ant (Iridomyrmex humilis). According to Wild (2004), this species was originally described in the genus Linepithema by Mayr in 1866; therefore, the proper binomial should be Linepithema humile. It is a small, dark-colored ant about 3 mm (1/8 inch) long that invades homes in search of food and water. They are especially fond of sweets, but will feed on practically any food. They love the yolks of hard boiled eggs and carry minute yellow clumps of yolk back to their nest in endless ant columns. These ants are extremely well adapted to urbanized areas of the United States with mild climates and well-watered gardens. They pose a serious threat to native wildlife by upsetting delicate food webs. They are especially formidable due to their aggressive behavior and the enormous size of their colonies which can literally "team up" with other colonies.

If you live in southern California, you probably have seen endless single file columns of uninvited six-legged guests walking through your home. They follow a pre-marked pheromone "scent" trail initially laid down by scouts who were searching for goodies in your pantry. Although they prefer the outdoor life style, they primarily enter houses for food and water. They are fond of sweets, tuna, syrups (even cough syrup), juices, eggs, dead spiders and rodents, vomit, feces and just about any other organic matter they can find. They are essentially scavengers and they play a valuable role in the natural ecosystem--but preferably in Argentina. In hot, dry weather they often search your home for water, including bathroom faucets and drains. I once followed an ant safari into my bathroom where they were neatly stacking their precious cargo of tiny eggs inside my toilet tank. They also relish the "honeydew" secretion of aphids, and protect their aphid friends from natural predators. In the fall months as the nights get chilly, they once again seek the warmth and shelter of your cozy home.

The first Argentine ants set foot on U.S. soils in the late 1890's, as coffee ships from Brazil unloaded their cargo in New Orleans. Being prolific breeders and constantly on the go, they moved across the southern half of the United States. A single colony may contain 10,000 female workers, and there may be hundreds of colonies around your home; the total number of ants could easily reach a million. Although they cannot sting, they can bite; however, they are only about 3 mm long and their tiny mandibles are too small to hurt humans. But, in the world of insects, these ants are truly a living terror. They are very aggressive and readily overtake other ant species, even ants that are much larger and with powerful stings. Argentine ants are relentless and simply outnumber their adversaries until the enemy colony is destroyed. They even attack paper wasp nests under the eaves of a house, forcing the huge wasps to flee their nests in terror. Even nests of large carpenter bees are no match for these relentless ants. A "killer bee" nest probably could not withstand an invasion of Argentine ants. They also will attack bird nests, driving off the mother bird and killing the helpless young. One possible redeeming quality about these little warriors is that they may attack dry-wood (aerial) termite colonies in your home. I have observed this Lilliputian massacre in a termite infested table in the Palomar College greenhouse.

Most ant colonies are very territorial, and will fight different colonies of the same species. Since Argentine ants in the United States originated from the original colonizers in Louisiana, they are all closely related with very similar DNA. They apparently will accept ants from different colonies as members of their gigantic family. In fact, Argentine ants from different colonies will actually "team up" and attack together in vast swarms. They simply outnumber and overpower their enemy.

Argentine ants have become a serious threat to the coast horned lizard (Phrynosoma coronatum) in southern California. The primary food source for these endangered lizards are native harvester ants, particularly the harvester ants (Pogonomyrmex) and (Messor). I spent many years observing this fascinating red ant while growing up in San Gabriel Valley, and I can personally testify that it has a painful sting. As of 2006, this large red ant is seldom seen in urbanized areas of coastal southern California.

Urbanization has certainly been a factor in the demise of California harvester ants, but an even greater factor resulting in the elimination of native ants and coast horned lizards is the aggressive Argentine ant. Apparently the horned lizard is not fond of Argentine ants, and is actually attacked by them in enormous swarms. Colonies of Argentine ants need a damp area to survive, and have not invaded some of the dry habitats where native harvester ants and desert horned lizards (P. platyrhinos) still live. Of course, they can readily colonize urbanized desert areas inhabited by people. Well-watered gardens with stepping stones and concrete slabs provide the idea living requirements for these ants. In their native Argentina they live under rocks.

Argentine ants are a terrible nuisance in gardens and orchards because they tend and protect scale insects and aphids. They even carry aphids to the tender buds of your prized roses. In return, the ants consume a sweet secretion from the aphids called "honeydew." In addition, swarms of these ants will invade orchard trees, destroying the fruit crop. This is especially serious in figs (Ficus carica) where the symbiotic pollinator wasps are destroyed.

According to entomologist David Faulkner, if you have a 10 x10 foot (3 x 3 m ) patio slab, you could have a million or more individuals and possibly 20 or 30 queens. They get along fine because they're all related to the original colonizers in Lousiana, perhaps from the original gravid (pregnant) female who arrived there. Workers live a month or more as adults, but queens live up to 10 years or more. With other ants, when the queen dies, the one-queen colony dies because no more ants are being produced. With multi-queen Argentine ants, another queen simply moves in and takes over the role of the deceased queen. In fact, a queen from San Diego would probably be accepted in a colony elsewhere in California.

I have compared Argentine ants with the "Borg" of Star Trek, a fictional cybernetic race controlled by drones. This is probably not an accurate comparison because the Borg apparently have centralized control by the "Borg Queen." Ant colonies exhibit "swarm intelligence" with the collective behavior of a decentralized system. The individual units (workers & soldiers) are sterile females that operate without a power hierarchy or permanent leader. The queen's role is basically an egg machine to reproduce and perpetuate the colony. The indivuals communicate with each other by the release of pheromones. Extreme warfare in ants arises from a social unity similar to cells in an organism. Cells are recognized as "self" by our immune system because of chemicals imbedded in the cell membranes. Some of these are special proteins (glycoproteins) with unique carbohydrate antennae. Just as foreign bacteria and viruses are recognized as "enemies" by our immune system, ants recognize rival colonies by different pheromones. Simplified diagram of cell membrane structure. This model shows large protein (glycoprotein) molecules embedded in the membrane. Membrane proteins may serve as carriers in which molecules and ions pass through channels in the protein. Glycoproteins may also be associated with cell recognition in which patrolling T-cells and antibodies recognize the shape of membrane proteins as "self" or "foreign." These membrane proteins often contain unique carbohydrate chains (antennae) which are involved in the cell recognition process.

In their native homeland of Argentina, different colonies of Argentine ants are not so friendly to each other because their DNA has developed much greater variation. Neighboring colonies may fight each other, even though they are only 200 yards (200 m) apart. Also there are many native predators in Argentina, including fungal parasites and bacteria. The narrow genetic variability that has kept all the California populations on friendly terms may eventually backfire due to excessive inbreeding. Perhaps some day these ants may not have the genetic variability to adapt to a changing environment.

Return To The WAYNE'S WORD Home Page Return To The NOTEWORTHY PLANTS Menu