Giant Ant Colony Takes Over the World?
Argentine ants/Copyright (c) 2009 Alex Wild
I kid you not, this story sounds just like a science fiction movie. A giant supercolony of ants has taken over the earth! But it’s true, in a roundabout sort of way, according to scientists. Most ants are social insects, meaning that they live in colonies and are often highly inter-related. They don’t compete with one another for mates and food, but collectively harvest, protect, and breed for the greater good of all the colony, often with one or a few breeding queens. Ants from neighboring colonies, though, act aggressively toward one another because they’re not relatives like individuals within each colony.
Some ant species form supercolonies, which spread for miles and miles. Argentine ants (Linepithema humile) live all around the world on every continent except Antarctica, having been introduced by people in various locales around the world from their native South America. One giant Argentine ant supercolony stretches for over 3,700 miles along the Mediterranean coast of Europe, another stretches 560 miles down the coast of California, and a third down the west coast of Japan. If you take ants from one side of the California colony and introduce them to ants at the other side of the coast, they treat one another as old friends, tickling antennae and saying hello. No aggression. But ants from different colonies will attack one another.
Here’s where it gets weird. Scientists from Japan and Spain decided to try a fun little experiment. They took ants from California, four known supercolonies in Japan, the European supercolony, and another smaller known colony in Catalonia in Europe. Then they had ant battles! The scientists matched up ants from various colonies to watch the ant fights. What happened next surprised everyone. They figured ants from different colonies would all act aggressive to one another, but ants from California and Japan and Europe all got along famously! But ants from the smaller supercolonies in Catalonia and Kobe, Japan acted aggressively toward ants from other colonies. What that means is that Argentine ants have one ginormous supercolony across the world and they’re all one big family.
Based on earlier research, the scientists think that the genetically related ants recognize one another from chemical similarities on their cuticle, which is the outer layer of the ant’s exoskeleton. They published their latest research in the scientific journal, Insectes Sociaux. Eiriki Sunamura, the lead scientist on the study, believes the introduced ants went through a “genetic bottleneck” when brought from their South American home to various locales around the world and hence the non-native populations have greatly reduced genetic diversity. That scenario is supported by another genetic study by researchers at the University of California, Berkeley, that shows the main supercolonies around the world are genetically very similar. Most likely, some ants have probably been accidentally brought around the world by people, further ensuring the populations don’t diverge genetically, and so they have remained as one giant mega-colony.