Ants are amazing diggers, constructing elaborate multi-tiered nests connected by an intricate network of tunnels, sometimes reaching depths of up to 25 feet. Now, a team of scientists from the California Institute of Technology has used X-ray imaging to capture the process of how ants build their tunnels. Scientists have found that ants have evolved to intuitively sense particles of grain that they can remove while keeping the structure stable, just like removing individual blocks in a game. jenga. The team described their work at new paper Published in Proceedings of the National Academy of Sciences.
Scientists interested in collective behavior have been studying ants for decades. This is because the ants, as a group, behave like some form of granular media. Few spaced ants behave as well as individual ants. but Pack enough of them Closely together and working as one unit, they exhibit solid and liquid properties. You can pour fire ants out of a teapot, for example, or the ants can link together to build floating towers or rafts. Ants may be small creatures with small brains, but these social insects are capable of it Organize themselves collectively In a highly efficient community to ensure the survival of the colony.
Several years agoBehavioral biologist Guy Theraolase from the Institute for Advanced Studies in Toulouse, France, and several colleagues combined laboratory experiments with Argentine ants and computer modeling in order to Define three simple rules Controlling the behavior of ants in digging tunnels. For intelligence: (1) ants pick up grains at a constant rate (about 2 grains every minute); (ii) Ants prefer to shed their grains near other grains to form plumes; and (3) ants usually select grains marked with a chemical pheromone after other ants have dealt with them. Theraolase and others. 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 the need for central coordination.
Recently, a paper 2020 I found that social dynamic How the division of labor emerges in an ant colony is similar to how political polarization develops in human social networks. Ants also excel at regulating their own traffic flow. a Study 2018 By Daniel Goldman’s group at Georgia Tech has researched how fire ants can improve tunneling efforts without causing traffic jams. as we are I mentioned at that 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 any one 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 the fire ants could actively feel the changes in the forces acting on their floating raft. Ants recognize different conditions for fluid flow and can adapt their behavior accordingly to keep the raft stable. An oar moving through the river water will create a series of whirlpools (known as a shedding vortex), causing the ants’ rafts to spin. These vortices can also exert additional forces on the raft, enough to break it apart. The changes in both the centrifugal forces and the shear forces acting on the raft are very small – perhaps 2 percent to 3 percent of the normal gravitational force. However, somehow, ants can feel these small shifts with their bodies.
This last paper focuses on western harvester ants (Pogonomyrmex occidentalis), was chosen because of its prolific ability to dig into soil grains at the millimeter scale. Co-author Jose Andrade, a mechanical engineer at Caltech, was inspired to explore tunneling ants after seeing examples of Ant’s nest art. The pieces are created by pouring some kind of molten metal, plaster or cement into the ant mound, which flows 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 “know” how to dig up those 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 if they knew what they were doing, but we started with the premise that they were digging in an intentional way,” Andrade said. “We hypothesized that the ants might have been playing jenga. “
In other words, the researchers suspected that ants roam the soil looking for loose grains to remove, in the same way that people search for loose clumps to remove them from jenga turret, leaving the critical bearing pieces in place. These blocks are part of what’s known as a “force chain” that jams blocks (or granular soil particles, in the case of an anthill) together 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 into several small cups of soil. The size of the cups was chosen for how easy they are to fit inside 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 while the ants were digging a tunnel to monitor their progress. From the resulting 3D images, they created a “digital avatar” for each part in the sample, capturing the shape, position and orientation of each grain – all of which can greatly affect the distribution of forces in soil samples. 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 in time.
The ants weren’t always cooperative when it came to seriously digging their tunnels. “They are kind of imitated.” Andrade said. “They dig whenever they want. We’d put these ants in a container, and some would start digging right away, and they’d make this amazing progress. But others – they will take hours and not dig at all. Some would dig for a while and then stop and rest.”
Andrade and Parker note some emerging patterns in their analysis. For example, ants usually burrow along the inner edges of the cups – an effective strategy, as the sides of the cups can be part of the structure of the tunnels, saving the ants a little effort. The 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 far as possible in a granular medium like soil is called “rest angle”; Exceed that angle, and the structure will collapse. Somehow, ants can sense this critical threshold, making sure that their tunnels do not go beyond the angle of rest.
For basic physics, the team discovered that when the ants removed soil grains to dig their tunnels, the force chains acting on the structure rearranged themselves from a random distribution to form a kind of liner around the outer tunnel. This redistribution of forces strengthens the existing tunnel walls and relieves the pressure the grains exert at the end of the tunnel, making it easier for ants to remove those grains to extend the tunnel even further.
“It has been a mystery in both engineering and ant ecology how ants build these decades-old structures,” he said. Parker said. “It turns out that by removing the grain in this pattern that we observed, the ants are taking advantage of these oceanic force chains as they burrow down.” Ants press on individual grains to assess the mechanical forces exerted on them.
Parker thinks it’s a kind of behavioral algorithm. This algorithm does not exist within a single ant. He said. “It’s the nascent colony behavior of all those workers who behave like superorganisms. How this behavioral program spreads through the micro-brains of all these ants is one of the wonders of the natural world for which we have no explanation.”
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