The Complex Engineering of Underground Ant Cities

The study was published in the journal PNAS.

A look at how ants build their underground burrows

The Caltech team, led by Jose Andrade, the George W. Housner professor of civil and mechanical engineering at Caltech, closely observed ants' behaviors to understand how they were deciding to build their constructions. 

Asking Joe Parker, the assistant professor of biology and biological engineering at Caltech, to join their team, the scientists cultured ants and put them in little cups filled with soil so that they could then put them in an X-ray imager. 

The team was able to create 3D scans of the inner tunnels the ants had created in the cups, and create simulations of their progress. In doing so, Andrade and his team realized the ants followed a few patterns: 

    1. They were efficient: They dug their tunnels along the sides of the cups and as straight as possible, minimizing any extra work.

As Andrade stated "That makes sense because a straight line is the shortest path between two points. And with them taking advantage of the sides of the container, it shows that the ants are very efficient at what they do."

    2. They dug their tunnels as steeply as possible without exceeding the steepness, perfectly abiding by the laws of physics — otherwise, the tunnels would collapse and the ants would die.

And the third, and final, discovery the team made was something that could serve humans with their underground digging techniques:

   3. As they remove grains of soil, they naturally rearrange the force chains in the tunnel.

This means that as they work, they create little cocoons around themselves, which reinforce the existing walls of the tunnel, and which relieve pressure from the grains at the section of the tunnel where the ants are working, making it easier for the ants to safely remove them. 

"It's been a mystery in both engineering and in ant ecology how ants build these structures that persist for decades," Parker said. "It turns out that by removing grains in this pattern that we observed, the ants benefit from these circumferential force chains as they dig down."

One of the most fascinating discoveries of this study is that the ants don't appear to even be aware of their work methods, it just comes naturally to them.

The hope is that in the future robotic ants could build tunnels for humans.