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How fire ants conquered the world

Reproductive queen of the invasive fire ant species Solenopsis invicta. Adult workers tend the queen and care for the brood (larvae and pupae visible in background). Assessment of genetic variation from 75 sites worldwide reveals that recent S. invicta infestations in California and several Pacific Rim countries appear to have originated from the southern USA, where this pest insect was introduced from its native South American range almost a century ago.
[Image courtesy of Kenneth G. Ross]

Fire ants get their name from how bad their sting feelsólike someone's lit a match against your skin. And their sting isn't the only thing about them that hurts. In the United States, people spend more than $6 billion every year trying to control the ants.

It wasn't always like this. In a new study, Marina Acsunce and her fellow scientists show how fire ants invaded the United States from Argentina more than 90 years ago. These ants were probably stowaways on a cargo ship. They made themselves at home in the southern United States, but quickly conquered the world.

Ascunce and colleagues compared the genes found in fire ants from 2144 ant colonies in 75 places to trace the ants' travels across the globe. Ants that started out in the same colony usually share some genes, even if the ants now live different places. The scientists used this fact to show how fire ants spread out from the southern United States in nine separate invasions. Today, you can find fire ants in California, the Caribbean, China, Taiwan, and Australia.

It's a pest problem that will probably get worse, the scientists say. As more people fly and sail around the world every year, the fire ants will come along for the ride and try to make a new home in a different place.


This research appears in the 25 February issue of the journal Science.