Ants use soil physics to excavate metre-long tunnels that last decades

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By Matthew Sparkes

Ant colonies tin descend respective metres underground, location millions of insects and past for decades, contempt being made without the payment of machinery and reinforcing material. The secrets of these awesome architectural structures are being revealed by three-dimensional X-ray imaging and machine simulations, and could beryllium utilized to make robotic mining machines.

José Andrade astatine the California Institute of Technology and his colleagues acceptable up miniature ant colonies successful a instrumentality holding 500 millilitres of ungraded and 15 occidental harvester ants (Pogonomyrmex occidentalis). The presumption of each ant and each atom of ungraded was past captured by high-resolution X-ray scans each 10 minutes for 20 hours.

The X-ray results gave researchers nonstop details astir the signifier of each passageway and which grains were being removed to make it. The squad past created a machine exemplary utilizing those scans to recognize the forces acting upon the tunnels. The size, signifier and predisposition of each atom was recreated successful the exemplary and the absorption and size of unit connected each atom could beryllium calculated, including gravity, friction and cohesion caused by humidity. The exemplary was close to the 0.07 millimetre solution of the scanner.

The results suggest that forces wrong the ungraded thin to wrapper astir the passageway axis arsenic ants excavate, forming what the squad telephone “arches” successful the ungraded that person a greater diameter than the passageway itself. This reduces the load acting connected the ungraded particles wrong the arches, wherever the ants are constructing their tunnel. As a result, the ants tin easy region these particles to widen the passageway without causing cave-ins. The arches besides marque the passageway stronger and much durable.

“We had naively thought that ants possibly were playing Jenga, that they were tapping, possibly they were wiggling grains, possibly they were adjacent grabbing the grains of slightest resistance,” says Andrade.  He says it is present wide that the ants look to cognize thing astir forces and amusement nary signs of decision-making, but alternatively travel a precise elemental behavioural algorithm that has evolved implicit time.

physical forces acting successful  soil

Before ants excavation tunnels, the grain-to-grain forces successful ungraded are randomly aligned (left), but arsenic the ants excavation (right), the forces align and wrapper astir the tunnel


The ants thin to excavation comparatively consecutive tunnels that descend astatine the space of repose – the slope astatine which a granular worldly people forms mounds – which was astir 40 degrees successful this case. They besides prime precisely the close grains to region to make a protective arch above.

“In a singular mode – successful a rather, you know, serendipitous mode – they’ve stumbled upon a method for digging that is successful enactment with the laws of physics, but incredibly efficient,” says Andrade.

The squad believes that if the behavioural algorithm tin beryllium further analysed and yet replicated, past it whitethorn find exertion successful automated mining robots, either present connected Earth oregon connected different planetary bodies wherever the already risky concern of mining would beryllium adjacent much unsafe for humans.

Journal reference: Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.2102267118

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