May 1, 2011 in Nation/World

Scientists solve fire ant mystery

Amina Khan Los Angeles Times

LOS ANGELES – The mystery behind the remarkable ability of fire ants to turn themselves into a living, crawling life raft has been unlocked by scientists: The insects use air pockets that form around their bodies to protect themselves from drowning.

The analysis was published online last week in the journal Proceedings of the National Academy of Sciences.

Fire ants can join into rafts that can survive flash floods in their native Brazilian rain forests.

But no one knew how these insects, which flounder and struggle in the water as individuals and whose bodies are denser than water and thus should sink, could float when they banded together.

To catch the ants in action, researchers collected fire ants off roadsides in Atlanta and brought them to their lab. The ants, they knew, behaved like a fluid: A handful could be molded and even poured. So the scientists swirled the ants in beakers until they formed spherical clumps, then dropped those ant balls into containers of water.

Quickly, the ants spread out into a pancake-like formation. The ants used their claws, adhesive pads on their legs and their mandibles to grip onto one another.

After freezing one of the rafts in liquid nitrogen, researchers using an electron microscope noticed how hairs allowed the insects to trap air bubbles. With so many ants jammed together, the bubbles fused to form a protective air layer for all of them.

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