Isaac Flooding Forces Fire Ants Afloat

September 4, 2012; 10:34 AM ET
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In this photograph, a fire ant is floating on pockets of air. Picture is courtesy of Mlot, Tovey and Hu, Georgia Tech.

Fire ants, locked into a living "raft," have been seen floating in areas of Florida recently flooded by Isaac.

Fire ants in the southeastern U.S. were first seen in the mid-1930s in Mobile, Ala., according to They are believed to have been transported there from South America by shipping.

Since that time, they have been spreading throughout the Southeast. Florida has colonies of fire ants in every county.

Rainfall from Isaac totaled 11.51 inches at the West Palm Beach International Airport. Residents in Palm Beach County are facing flooded roads containing fish and alligators, according to

In addition to those problems, fire ants may also be a concern.

In their native land in the wetlands of Brazil, it is common for the ants to face rain that can flood their colony. Sometimes the colonies are flooded twice a day, according to Dr. David Hu, assistant professor of Mechanical Engineering and Biology at Georgia Tech.

The fire ants have developed an unusual adaptation to deal with the floods. When an underground colony of fire ants becomes flooded with water, the ants are able to form a living "raft" and float to drier ground.

A fire ant mass is floating on water in this picture. Photo by Mlot, Tovey and Hu, Georgia Tech.

The colony does this by linking together and trapping air. "They form into two layers of ants and place their ant larvae and young ants on the top layer," said Hu. "Their bodies are surrounded by plastron (a layer of air) that is constantly replenished."

Only the bottom layer of ants gets wet, and all of them are able to breathe.

In this form, they are very strong. "They decrease their density by five and they can withstand some force," said Hu. When the ant mass is pushed underwater, it immediately resurfaces.

The ants are able to remain locked into a floating mass for sometimes up to a few months. If they need nourishment, they will eat their young.

Dr. Hu said that there are other species of ants that can also form floating masses.

Floating fire ants may also be in flood-waters of Mississippi, Georgia and Louisiana.

If you spot a mass of ants floating along, it is best to leave them alone. Fire ants bite and deliver a burning sensation that later forms into a small pustule. The ants are capable of biting multiple times.

A close-up shot of the floating mass of fire ants was provided by Mlot, Tovey and Hu, Georgia Tech. The worker ants on the top layer can be seen holding the ant larvae.


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