Linepithema humile is a dark ant native to northern Argentina, Uruguay, Paraguay, and southern Brazil. The workers are only about three millimeters long and live in the ground. The ants are dominant and aggressive and, by accident, have been introduced to all continents except Antarctic.
Ants Form Vast Colonies
According to the Global Invasive Species Database Linepithema humile (the Argentine ant) is very invasive and it identifies them as among 100 of the “World’s Worst” invaders. The ants form “fast growing, high-density colonies, which place huge pressures on native ecosystems…[it] is the greatest threat to the survival of various endemic Hawaiian arthropods and displaces native ant species around the world (some of which may be important seed-dispersers or plant-pollinators) resulting in a decrease in ant biodiversity and the disruption of native ecosystems.”
Matt Walker, Editor of Earth News at the BBC writes (July 1, 2009) that the Argentine ants have created enormous colonies.
“In Europe, one vast colony of Argentine ants is thought to stretch for 6,000km (3,700 miles) along the Mediterranean coast, while another in the U.S., known as the ‘Californian large,’ extends over 900km (560 miles) along the coast of California.” Another mammoth colony is on the west coast of Japan.
Ants Share Similarities across Continents
Eiriki Sunamura of the University of Tokyo and a team of researchers from Japan and Spain have been studying the ants. They have found that those living in locations as widely spaced as Europe, Japan, and California share a chemical profile of hydrocarbons on their cuticles that is strikingly similar.
The researchers collected live ants from various locations and carried out tests to see if individuals from one colony would be aggressive towards those from another.
Commenting on the study BBC News reported that…“whenever ants from the main European and Californian super-colonies and those from the largest colony in Japan came into contact, they acted as if they were old friends.
“These ants rubbed antennae with one another and never became aggressive…In short, they acted as if they all belonged to the same colony.”
Do Ants Form a Single Global Super-colony?
Writing in the July 2009 issue of the scientific journal Insectes Sociaux, the research team says, “The enormous extent of this population is paralleled only by human society.” And that “Humans created this great non-aggressive ant population,” by introducing the ants to areas of the world in which they are not normally found.
However, there is debate among those who study the Argentine ant about the nature of these super-colonies. The discussion is outlined at the Myrmecos Blog. The classic theory is that the ants went through a genetic bottleneck when introduced to new areas “and the resulting homogenous population lacked the genetic diversity needed to recognize nestmates from non-nestmates.”
More recently, researchers have said the Argentine ant created super-colonies in their native habitats and that they are replicating this behaviour in the regions to which they have been introduced.
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