Contributed by Stephen Berecki
The Argentine ant is an invasive species that has spread from its native home in South America to most of the globe. They are now found on all continents (other than Antarctica), and are displacing the native ant species with which they come into contact. As a result, they are disrupting other organisms as well. For example, some lizards depend on specific ants for food and if those ants are gone, the lizards are in trouble. These ants have spread mostly thanks to humans. Crossing over large areas by hitching a ride with humans (or any other way it can hitch a ride) is called long-distance-jump-dispersal. This is the only way these critters can cross oceans and impenetrable landscapes. The Argentine ants are unique in the fact that the queens do not fly to new areas to make new colonies. This means they rely on walking to a new area if they want to colonize it. If there is a body of water, mountains, or just a large patch of unfavorable land, it is basically impossible for these small animals to make the journey on their own. This is why the Argentine ant mostly relies on humans to spread to other areas.
Argentine Ants (image from Wikimedia Commons)
There are a few reasons why the Argentine ant is so successful in competition with other ant species. The simplest is the fact that in lands far away from home, they escape from predators and parasites. One example is the phorid fly that parasitizes only the Argentine ant. Phorid flies lay eggs inside the ant and the larvae eat the ant, resulting in a nasty death. Another reason the Argentine ant is so successful is that all of the different Argentine ant colonies are not hostile towards each other, which is called unicoloniality. Most ants will only be friendly towards members of the same colony, even if it means competing with other colonies of the same species. This gives the Argentine ants a distinct advantage because they are not all competing with each other. Instead of a bunch of small ant colonies competing with each other, it’s a bunch of small ant colonies competing against a huge united Argentine ant colony. The final main reason for success is these ants are clever by harvesting sugars (i.e., honeydew) from other insects, like aphids. The ants will protect these insects and, in return, the insects produce sugars for the ants to eat. This is like humans milking cows or collecting chicken eggs. This might be one of the only other examples of husbandry by any other animal besides humans.
Argentine ants are a menace for other ant species they come across as they invade new lands. As they displace and remove other ants from their native lands, the Argentine ants are disrupting entire ecosystems. By displacing other ant species, they are removing food sources from other animals that rely on those ant species as their source of food. They can also have a direct impact on agriculture as well. By protecting aphids and scale insects they are hurting crops of nearby farmers. Aphids and scale insects are pests that eat crops.
If we want reverse the trend of the invasive Argentine ants then we must do something about it ourselves. One possible way to remove these ants is to introduce the phorid flies to areas where Argentine ants are a problem. This has already been done in Texas where they introduced similar flies to the area to deal with the fire ant problem. This strategy however could be a very dangerous thing to do. As often the case, introducing an invasive species to deal with another invasive species can backfire very easily. The phorid flies could start parasitizing other native species as well and this could be disastrous.
Suarez AV, Holway DA, Case TJ. (JAN2001). Patterns of spread in biological invasions dominated by long-distance jump dispersal: Insights from Argentine ants. PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, Vol. 98, 1095-1100.
Holway DA. (JAN1999). Competitive mechanisms underlying the displacement of native ants by the invasive Argentine ant. ECOLOGY, Vol. 80, 238-251.
Science Daily. September 29th, 2006. Fire Ant-Attacking Fly Spreading Rapidly in Texas. http://www.sciencedaily.com/releases/2006/09/060927110742.htm