By Dr David Whitehouse
BBC News Online science editor
Army ants, these days dispersed across the world, all came from a single source over 100 million years ago on the ancient supercontinent of Gondwana.
Army ants have been around for over 100 million years
A new study indicates the insects all share identical genetic markers that reveal a common ancestor.
Many scientists believed that army ants originated separately on several continents relatively recently in Earth history.
But the new research means that army ants join animals such as sharks and crocodiles that have remained relatively unchanged for many tens of millions of years.
Army ants are unlike the ants found at family picnics. They are in general nomadic, foraging for prey without advance scouting, and their wingless queens can produce up to four million eggs in a month.
Because army ants are found almost everywhere, scientists postulated that they evolved many times after the break-up and dispersal of the supercontinent Gondwana just over 100 million years ago.
The conventional view of the evolution of army ants needs a revision because of new data obtained by Sean Brady, a Cornell University, US, entomologist who has discovered that these ants evolved from a common ancestor.
"Biologists have wondered why army ants, whose queens can't fly or get caught up by the wind, are so similar all around the world," he says.
The answer is that "army ants have evolved only once and that was in the mid-Cretaceous period".
Genetic family tree
Brady studied the DNA of 30 army ant species and 20 possible ancestors within the ant community, looking specifically for genetic clues to their relationships.
"Essentially, I built a genetic family tree. Then I took that family tree and looked at its genetic tree rings to postulate what happened in the past," he says.
Combining the genetic data with fossil information, Brady found that all the species share the same genetic mutations.
"If they share those mutations, we can infer they evolved from the same source," Brady says.
His research is published in the Proceedings of the National Academy of Science (PNAS) journal.