Ant colonies can descend several metres underground, house millions of insects and last for decades, despite being made without the benefit of machinery and reinforcing material. The secrets of these impressive architectural structures are being revealed by three-dimensional X-ray imaging and computer simulations, and could be used to develop robotic mining machines. José Andrade at the California Institute of Technology and his colleagues set up miniature ant colonies in a container holding 500 millilitres of soil and 15 western harvester ants (Pogonomyrmex occidentalis). The position of every ant and every grain of soil was then captured by high-resolution X-ray scans every 10 minutes for 20 hours. The X-ray results gave researchers exact details about the shape of each tunnel and which grains were being removed to create it.