Ants create stable tunnels in nests, just like humans who play jinga

Ants are incredible diggers, building elaborate multi-level nests connected by an intricate network of tunnels, sometimes reaching depths of up to 25 feet. Today, a team of scientists from the California Institute of Technology used x-ray imaging to capture the process by which ants build their tunnels. Scientists have found that ants have evolved to intuitively detect grain particles that they can remove while keeping the structure stable, much like removing individual blocks in a game. jenga. The team described their work in a new article published in the Proceedings of the National Academy of Sciences.

Scientists interested in collective behavior have been studying ants for decades. This is because ants, as a group, behave like a form of granular medium. Few spaced ants behave as well as individual ants. But pack enough of them tightly together and act as a single unit, exhibiting solid and liquid properties. You can pour fire ants from a teapot, for example, or the ants can link together to build towers or floating rafts. Ants can be small creatures with small brains, but these social insects are able to organize collectively into a very effective community to ensure the survival of the colony.

Several years ago, behavioral biologist Guy Theraulaz of the Institute for Advanced Studies in Toulouse, France, and several colleagues combined laboratory experiments with Argentine ants and computer modeling to identify three simple rules governing the behavior of ants in tunnels. For intelligence: (1) ants pick up kernels at a constant rate (about 2 kernels per minute); (ii) Ants prefer to lay their kernels near other kernels to form plumes; and (3) ants usually select kernels marked with a chemical pheromone after other ants have treated them. Theraolase ??. He built a computer simulation based on these three rules and found that after a week the virtual ants had built a structure very similar to real ant nests. They conclude that these rules emerge from local interactions between individual ants, without central coordination being necessary.

More recently, a 2020 article revealed that the social dynamics of how the division of labor emerges in an ant colony is similar to how political polarization develops in human social networks. Ants are also good at regulating their own flow of traffic. A 2018 study by Daniel Goldman’s group at Georgia Tech looked at how fire ants can improve tunneling efforts without causing traffic jams. As we reported at the time, the group concluded that when an ant encounters a tunnel in which other ants are already running, it retreats to find another tunnel. And only a small part of the colony digs at a time: 30 percent of them do 70 percent of the work.

David Ho’s biological locomotion group at Georgia Tech also studied fire ants. In 2019, he and his colleagues reported that fire ants can actively detect changes in the forces acting on their floating raft. Ants recognize different fluid flow conditions and can adapt their behavior accordingly to maintain the stability of the raft. An oar moving through the water of the river will create a series of whirlpools (known as a fall vortex), causing the ants’ rafts to rotate. These vortices can also exert additional forces on the raft, enough to break it. The changes in the centrifugal forces and the shear forces acting on the raft are very small – perhaps 2 to 3 percent of the normal gravitational force. However, one way or another, ants can feel these small changes with their bodies.

This last article focuses on Western harvester ants (Pogonomyrmex occidentalis), was chosen because of its prolific ability to dig into soil grains on a millimeter scale. Co-author Jose Andrade, Mechanical Engineer at Caltech, was inspired to explore tunnel ants after seeing examples of anthill art. Pieces are created by pouring some kind of molten metal, plaster or cement into the anthill, which passes through all the tunnels and eventually solidifies. The surrounding soil is then removed to reveal the final complex structure. Andrade was so impressed that he began to wonder if the ants really “knew” how to dig up these structures.

Andrade collaborated with Caltech bioengineer Joe Parker on the project; Parker’s research focuses on the ecological relationships of ants with other species. “We didn’t interview any ants to ask them if they know what they’re doing, but we started out by assuming that they are digging intentionally,” Andrade said. “We hypothesized that the ants could have played jenga. “

In other words, the researchers suspected that the ants scoured the ground for loose grains to remove, in the same way that people look for loose clumps to remove them. jenga turret, leaving critical support pieces in place. These blocks are part of what is called a “chain of force” that blocks the blocks (or granular soil particles, in the case of an anthill) to create a stable structure.

For their experiments, Andrade and his colleagues mixed 500 ml of koekret soil with 20 ml of water and placed the mixture in several small cups of soil. The size of the wells was chosen based on their ease of insertion into the CT scanner. Through trial and error, starting with a single ant and gradually increasing the number, the researchers determined the number of ants needed to achieve the optimal digging rate: 15.

The team took four and a half minutes every 10 minutes as the ants tunneled to monitor their progress. From the resulting 3D images, they created a “digital avatar” for each part of the sample, capturing the shape, position and orientation of each grain, which can greatly affect the distribution of forces in the samples. ground. The researchers were also able to learn the order in which each bead was removed by the ants by comparing images taken in different states over time.

Ants weren’t always cooperative when it came to seriously digging their tunnels. “They’re kind of imitated,” Andrade said. “They dig when they want. We would put these ants in a container, and some would start digging right away, and they would make amazing progress. But others – they will take hours and not dig at all. Some would dig for a while, then stop and rest.

Andrade and Parker note some emerging patterns in their analysis. For example, ants usually dig along the inner edges of cups – an effective strategy, as the sides of the cups can be part of the structure of the tunnels, saving them a bit of effort. Ants also preferred the straight lines of their tunnels, a technique that improves efficiency. The ants tended to dig their tunnels as hard as possible. As much as possible in a granular medium such as soil is called “angle of repose”; Go beyond this angle and the structure will collapse. Either way, ants can detect this critical threshold, making sure their tunnels do not exceed the angle of repose.

For basic physics, the team found that when ants removed the grains of soil to dig their tunnels, the chains of force acting on the structure rearranged from a random distribution to form a kind of coating around the outer tunnel. This redistribution of forces strengthens the existing tunnel walls and relieves the pressure exerted by the kernels at the end of the tunnel, making it easier for ants to remove these kernels to expand the tunnel even further.

“How ants build these decades-old structures is a mystery in both engineering and ant ecology,” Parker said. “It turns out that by removing the grain in this pattern that we have observed, the ants take advantage of these chains of oceanic force as they burrow.” The ants press down on individual grains to assess the mechanical forces exerted on them.

Parker thinks it’s some sort of behavioral algorithm. “This algorithm does not exist inside a single ant,” he said. “This is the emerging behavior of the colonies of all these workers who behave like superorganisms. The way this behavioral program spreads through the micro-brains of all of these ants is one of the wonders of the natural world for which we have no explanation.

DOI: PNAS ، 2021. 10.1073 / pnas.2102267118 (حول DOIs).