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Fleeting Wonders: Ants Turn Themselves Into Giant Raft To Carry Queen Through Floods

Fire ants weave themselves into rafts when faced with water. (Photo: Junglecat/Wikimedia Commons CC BY-SA 3.0

On October 4, folks in Greenville, South Carolina spotted what looked like a patch of dried mud, or a large floating burger patty, bobbing along the surface of flood water. On closer inspection, the blob revealed itself to be something much more intriguing: a squirming raft of fire ants that had woven together to ride out the flood.

Fire ants (Solenopsis invicta) band together to stay afloat, forming a watertight structure that keeps even the bottom ants alive thanks to tiny body hairs that trap a layer of air, preventing them from even being submerged. 

Portrait of a red imported fire ant, Solenopsis invicta. This species arrived to the southeastern United States from South America in the 1930s.

Those tiny hairs help keep even the very bottom ants from being submerged. (Photo: Insects Unlocked/Wikimedia Commons CC-Zero)

These species of ants, originally from South America, usually form mounds on land. But when faced with a deluge of rain, they’ll form an island and prop their queen on top—along with all their precious larvae—then float until they can form a new mound downstream. We already know ants have the ability to take over the world, but fire ants are the only ant species known with this specific raft-building capability. Apparently they can remain in this raft formation for weeks. Weeks!

A single ant is naturally very buoyant and can walk on water, thanks to surface tension and water-repelling (hydrophobic) feet. However, it shouldn’t work this way for larger masses, which is why ant rafts were initially puzzling. But when researchers looked closer, they found that when the ants wove themselves together, their collective water repellency increased.

How exactly do the little critters do it? Close inspection of one of their ant rafts reveals that the fire ants prefer to link legs in their version of a hand-to-hand grip. Holding on is tricky, though, since they must control the strength of their grasp so as not to cause each other harm. And it’s a bit of a forced team effort; ants up top will try to leave the pile, only to find that they’re completely stranded, and then end up sucked back into the center of the raft.

Clusters of fire ants are shown to act like a fluid (like this cup of fire ant coffee), or, as a Georgia Tech researcher described it, like soft putty. “You could give [a ball of ants] a squeeze. You could toss it in the air and the ants would stay together,” graduate student Nathan Mlot told National Geographic.

And once again, ant teamwork puts the rest of the world’s species to shame.

Every day, we track down a fleeting wonder—something amazing that’s only happening right now. Have a tip for us? Tell us about it: cara@atlasobscura.com.