The Physics of Ants and Ketchup

Of course, when there’s an article to be written about bugs, guess who gets it? That’s right…yours truly!

So what exactly do ants and ketchup have in common? Don’t get too bugged out. It’s only physics!

Live fire ants in a rheometer machine. Credit: Georgia Tech
Live fire ants in a rheometer machine. Credit: Georgia Tech

Groups of ants – called ‘aggregations’ – are able to change shapes and tasks based on the demands of their environment. For instance, when faced with floodwaters, they form rafts to stay alive. They can even use their bodies to build bridges. But what gives them this remarkable ability?

According to new research from the Georgia Institute of Technology, it’s because the insects are actually liquid-like and solid-like simultaneously.

The Georgia Tech researchers put thousands of fire ants into a rheometer, a machine used to test the solid-like and liquid-like response of materials such as food, hand cream or melted plastic. The ants were then sheared at constant speeds from about 0.0001 rpm up to about 100 rpm. By doing this, the researchers found the behavior of live ants was similar to that of dead ants: when the aggregation is forced to flow, live ants let go and play dead. In this case, the viscosity dramatically decreased as the speed increased.

“It’s not unlike ketchup,” said Alberto Fernandez-Nieves, an associate 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.”

The complete article is available here. There’s even a video sample of an experiment with a penny. Oodles of oozing science!


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