Ant Engineering: A liquid and a Solid?

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The ants are remarkably social, relying on each other for their own survival. When together, the ants act as a single unit, comparable to a liquid, or as Georgia Tech describes, like ketchup. When a penny was dropped onto the collection of ants, the insects temporarily disconnected their grasps on one another to allow the penny to flow right through the colony, then self-assembled again after the coin passed.

The collection of ants have the ability to change shapes and act in different ways based on the tasks at hand to better interact with the environment. Water to a single ant is often deadly, but to the fire ants, it can be a great method of transportation. When floodwaters hit, the ants self-assemble into a "solid" mass that has incredible buoyancy which keeps them above the water, high and dry (unless they, of course, are the ones on the bottom). The ants have also been known to build bridges and span gaps many times the length of their own size.

“It’s not unlike ketchup,”

Says Alberto Fernandez-Nieves, a professor in the School of Physics.

“The harder you squeeze, the easier it flows. But with ants, this happens much more dramatically than with ketchup.”

What is going on?

Research conducted at the Georgia Institute of Technology claims the ants can pull off these magnificent feats because the insects act like as a liquid and solid simultaneously- superfluid ants if you will. The ants were put inside a rheometer (see picture below- essentially a device that tests the solid and liquid properties of foods) where they were spun at constant speeds from about 0.0001 rpm up to about 100 rpm. It was discovered by researchers that when spun at higher speeds, the behavior of the live ants was similar to that of the dead ants: under higher forces, the ants let go and played dead despite having the strength to hold on much longer (don't worry, they were okay). It was discovered the ants did this in order to protect the other ants from becoming injured or killed under the forces, despite wanting to stick together as a colony.

Ants in the rheometer, a machine that tests the solid-like and liquid-like response of materials [Image Source: Georgia Tech]

“Ants seem to have an on/off switch in that they let go for sufficiently large applied forces,”

Says David Hu, another professor from George W. Woodruff School of Mechanical Engineering.

“Despite wanting to be together, they let go and behave like a fluid to prevent getting injured or killed.”

The same mechanism was discovered in the penny drop experiment. Ants flowed around the coin to allow it to sink to the bottom where it can cause no harm. However, when the ants were (scientifically) poked, they respond like a spring and quickly return to their original shape, demonstrating aspects generally atributed to solid rubber like substances.

Ants acting as a solid, springy material [Image Source: Georgia Tech]

“This is the hallmark of viscoelastic behavior,”

Said Fernandez-Nieves.

“The ants exhibit a springy-response when probed at short times, but behave fluid-like at longer times.”

It was determined that ants are equally solid and liquid-like. Allowing them to adapt in different environment scenarios, giving them an advantageous edge with their dual specialities.

Ants acting as a liquid and solid while some "flow" out from the bottom as some remain "solid" - Similar to a non-Newtonian fluid [Image Source: Georgia Tech]

“Remarkably, the observed behavior is similar to what is seen in materials that are not alive, like polymer gels right at the point when they become a gel,”

said Fernandez-Nieves.

“This is quite puzzling, and we are now performing many more experiments to try and understand where these similarities arise from and how much they can be pushed. Doing this will hopefully extend our current way of thinking about materials, that like the ants, are active and thus out-of-equilibrium. There is much more interesting work we plan on doing with ants.”

The puzzling feature of ants is comparable to maximizing the most out of a jello package. At the max point, it would be somewhat solid, but also somewhat liquidy. The jello is similar to the properties of the ants, acting as a solid and a liquid. But perhaps the most perplexing thing about ants is the way they conform after being split in half.

"They’re like liquid metal – just like that scene in the Terminator movie.”

Says Hu, who claims the flexibility of the ants allows them to enjoy the best of both sides and take advantage of many situations. Instead of splitting off and dispersing, the ants work together and allow passage of materials and then reconect to create a "solid" mass.

  [Image Source: Georgia Tech]

Ants have the ability to act as a liquid, but also have the ability to float like a solid raft. Current studies are trying to determine if the abilities of ants can be attributed and recreated in other materials to create self-assemble and self-heal properties which could see applications in many areas including robotics and military sectors. For now, the mysterious surprising little creatures remain an engineering marvel with their ingenious survival techniques that one day soon, human engineers may be able to recreate.

SEE ALSO: Cooperative Robots Scale Walls Like Ants