Video: Ants Act Like Both Liquids and Solids

A ball of fire ants, which can act like liquids and solids. Courtesy of Georgia Tech

Put a bunch of fire ants into water, and they'll link their bodies together to form a solid ball that can float on the surface, transforming into a raft-like assemblage. Put that ball of ants on dry land, though, and it will "melt" away as the ants decouple and scurry off.

These attributes—along with other amazing abilities, like creating bridges with their bodies that other ants can climb across—inspired a group of materials scientists and physicists to perform a variety of tests on the animals. Their primary question: Do ants act like liquids or solids?

The answer is they act like both, says Alberto Fernandez-Nieves, a physicist at the Georgia Institute of Technology who normally studies (nonliving) soft condensed matter such as liquids and gels. If you, for example, drop a penny through a slot into a container full of fire ants (and who hasn't?!), the creatures will move away and let the coin slowly fall to the bottom, as though it is passing through a thick liquid. On the other hand, if you softly press upon a ball of ants, the blob compresses slightly but will elastically rebound like a solid.

The team put fire ants into a device called a rheometer, which is normally used to test the physical attributes of gels and liquids. In one test, they compressed ants between two plates and then recorded what happened when they slid one plate past the other and back again. When this action was performed slowly, the ants acted a liquid and allowed the plate to pass without friction, but when the sliding happened quickly, the ants jiggled like Jell-O.

The findings, detailed in a study published Monday in the journal Nature Materials, could have applications for developing materials that might act like the ants. Such a material doesn't yet exist. But its attributes—the ability to be strong like a solid, to flow like a liquid and to self-heal from wounds or breaks—would make it highly desirable.

In a sense, the ants behave somewhat like the T-1000, the shape-shifting android assassin in Terminator 2, which could heal itself and become liquid when desired, Fernandez-Nieves says.

"We think that's pretty cool," he adds.