When water levels rise, red fire ants (Solenopsis invicta) stream from their nests and rapidly grip onto their nearest neighbors in order to form rafts to carry them to safety. Each individual ant is denser than water and is in danger of sinking. However, the ants somehow manage to stay afloat, and they don’t just draw the line at constructing rafts — they routinely form bivouacs, assemble towers, and even coalesce into droplets when swished in a cup.
“You can consider them as both a fluid and a solid,” said David Hu from the Georgia Institute of Technology, who teamed up with Paul Foster and Nathan Mlot to investigate how balls of living fire ants self-assemble.