Tunneling for tumbling ants

Why are ant tunnels so uniform in diameter? If you guessed for ease of movement, you'd be only partially right. Ants do need their tunnels to be accessible passageways, but there's a more important reason for building them to such exacting specifications. It seems that ants construct their tunnels of the optimal size to catch them when they fall down the shafts, something that happens a lot more often than you might suspect. Ants are surprisingly clumsy travelers.

Say what you will about fire ants (Solenopsis invicta), they’re experts at building complex underground pathways. They’re also readily available around the Georgia Institute of Technology, which is where Daniel Goldman and his team work. 

The researchers collected the ants and provided them with soils containing a variety of particle sizes and moisture contents. Regardless of the substrate, the ants constructed tunnels with the same diameter. The tunnels varied in length and direction, but were always slightly wider across than one ant length. You might think this width was selected for as the smallest size that still permits rapid movement. However that wasn't the case. 

In a rather surprising discovery, the scientists found that ants use their antennae to catch themselves as they tumble down vertical tunnels. This suggests that tunnel diameters may be optimized not so much for rapid deployment as for letting ants recover from slips. 

If you want to see examples of an ant slipping down a tunnel, check out this video of Goldman explaining their work.

By the way, as interesting as these studies are, and who doesn’t find ants fascinating, Goldman and his colleagues have another purpose. They hope to someday be able to apply what they learn to the field of robotics. After all, ants are experts at building uniform structures out of diverse materials. As he explains:

Lots of the materials in disaster sites - landslides, rubble piles - are loose materials, which you're going to potentially have to create structures out of.

If all goes well, in future disaster zones we could have multitudes of mechanical ants or little robots that look like  cockroaches that will swarm all over the place.

Gravish, N., Monaenkova, D., Goodisman, M., & Goldman, D. (2013). Climbing, falling, and jamming during ant locomotion in confined environments Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.1302428110.