The study, published August 17 in Science, shows that not all nearby ants attempt to dig a tunnel simultaneously.
“We noticed that if you have 150 ants in a container, only 10 or 15 of them will actually be digging in the tunnels at any given time,” said Professor Daniel Goldman. “We wanted to know why, and to understand how basic laws of physics might be at work. We found a functional, community benefit to this seeming inequality in the work environment. Without it, digging just doesn’t get done.”
By painting 30 ants, it was discovered that 30% of the ants were doing 70% of the work. However, when the five hardest-working ants were removed, productivity remained the same from the remaining 25 ants.
The ant tunnels are narrow – barely wide enough for two ants to pass, according to GaTech – and the ants know how to avoid creating clogs by retreating from tunnels already occupied by other workers and sometimes idling.
“While observing the ants, we were surprised to see that individuals would sometimes go to the tunnel and if they encountered even a small amount of clog, they’d just turn around and retreat,” said Goldman. “When we put those rules into combinations with the robots, that created a good strategy for digging rapidly with low amounts of energy use per robot.”
Three robot behaviours were tried in the robots: ‘eager’ (all four robots plunged into the work), ‘reversal’ (robots gave up and turned around when they encountered delays reaching the work site) or ‘lazy’ (dawdling encouraged).
“Eager is the best strategy if you only have three robots, but if you add a fourth, that behaviour tanks because they get in each other’s way,” said Goldman. “Reversal produces relatively sane and sensible digging. It is not the fastest strategy, but there are no jams. If you look at energy consumed, lazy is the best course.”
With the University of Colorado Boulder, the ants were modelled using a technique called cellular automata.
“From our modelling, we learned that the ants are working right at the peak of the diagram. The right mix of unequal work distributions and reversal behaviours has the benefit of keeping them moving at maximum efficiency without jamming,” said Goldman.
The work is published as ‘Collective clog control: optimizing traffic flow in confined biological and robophysical excavation’.