Invaders by Sea: Imported Fire Ants

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Tramp freighter ship typical of one that may have brought red imported fire ants to the U.S. from Brazil in the 1930’s. Photo courtesy of

Red imported fire ants are not native to the southern United States. They are native to Brazil and Argentina. In the late 1920s, the ants are thought to have been imported on a ship from Brazil that landed in Mobile, Alabama loaded with products to sell in the United States.

As the ship was being unloaded and then reloaded with materials to take back to South America, the dock workers removed soil that was used for ballast in the hold of the ship. The soil was dumped out at the port in Mobile. Unknown to the dock workers, fire ants were living in the soil that was dumped from the ship.

Photo of freighter showing ballast and hold. Photo courtesy of

Because of this accidental introduction of fire ants, we now see black and red imported fire ants across a large part of the southern United States and in isolated areas of southern California. Fire ants are somewhat limited by cold weather. As a result, areas where winter temperatures drop down to 15 °F may have few to no fire ants at all.


*Test Yourself – What do these words mean?

  1. ballast
  2. hold (noun)
  3. imported
  4. native



Check out these experiments you can do to learn more about how these South American fire ants came to the United States.