Ants that travelled the world by sea

Do you know how tropical fire ants from Mexico crossed the Pacific ocean to reach the Philippines, and from there to other parts of the world?

Researchers now know the invasion history of the tropical fire ant, the first ant species known to travel the globe by sea.

A new study reveals that 16th century Spanish galleons shuttled tropical fire ants from Acapulco, Mexico, across the Pacific to the Philippines, and from there to other parts of the world.

Today, the ant species is found in virtually all tropical regions, including in Africa, the Americas, Australia, India and Southeast Asia.

"A lot of these ships, particularly if they were going somewhere to pick up commerce, would fill their ballast with soil and then they would dump the soil out in a new port and replace it with cargo," said study author Andrew Suarez from the University of Illinois.

"They were unknowingly moving huge numbers of organisms in the ballast soil," he explained.

"Invasive ants are a huge problem. Once they arrive, they establish really high densities in new habitats, with negative consequences for agriculture, native species and human quality of life," said co-researcher Sara Helms Cahan from the University of Vermont.

Controlling these ants costs millions of dollars annually.

The researchers analysed the genomes of tropical fire ants from 192 locales, looking at patterns of genetic diversity.

The team also analysed the trading patterns of Spanish sailing vessels going to and from the New World in the mid-1600s.

"If you look at the records, you look at the history, you look at the old trading routes and you look at the genetics, it all paints this picture that this was one of the first global invasions, and it coincided with what could be the first global trade pattern of the Spanish," Suarez said.

"The ants from the introduced areas in the Old World are genetically most similar to ants from southwestern Mexico, suggesting that their source population came from this region," he added.

The findings were reported in the journal Molecular Ecology.