The physics of fire ant rafts could help engineers design swarming robots

Victoria D. Doty

Noah rode out his flood in an ark. Winnie-the-Pooh experienced an upside-down umbrella. Fire ants (Solenopsis invicta), meanwhile, sort floating rafts produced up of thousands or even hundreds of thousands of individual insects.

A new study by engineers at CU Boulder lays out the simple physics-based mostly guidelines that govern how these ant rafts morph more than time: shrinking, increasing or rising long protrusions like an elephant’s trunk. The team’s conclusions could one particular day assist scientists style and design robots that operate jointly in swarms or following-technology components in which molecules migrate to take care of destroyed places.

The final results appeared recenty in the journal PLOS Computational Biology.

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“The origins of such behaviors lie in quite straightforward policies,” claimed Franck Vernerey, primary investigator on the new analyze and professor in the Paul M. Rady Section of Mechanical Engineering. “Single ants are not as sensible as just one may perhaps consider, but, collectively, they come to be very smart and resilient communities.”

Fire ants type these big floating blobs of wriggling bugs right after storms in the southeastern United States to survive raging waters.

In their newest research, Vernerey and guide writer Robert Wagner drew on mathematical simulations, or styles, to check out to determine out the mechanics fundamental these lifeboats. They uncovered, for example, that the a lot quicker the ants in a raft shift, the a lot more these rafts will develop outward, frequently forming long protrusions.

“This actions could, effectively, happen spontaneously,” stated Wagner, a graduate student in mechanical engineering. “There doesn’t necessarily need to be any central determination-creating by the ants.”

Treadmill time

Wagner and Vernerey identified the techniques of ant rafts just about by accident.

In a separate analyze printed in 2021, the duo dropped 1000’s of fireplace ants into a bucket of water with a plastic rod in the middle—like a lone reed in the center of stormy waters. Then they waited.

“We still left them in there for up to 8 several hours to observe the extended-term evolution of these rafts,” Wagner reported. “What we ended up observing is that the rafts started out forming these growths.”

Alternatively than keep the identical shape in excess of time, the structures would compress, drawing in to kind dense circles of ants. At other details, the bugs would lover out like pancake batter on a skillet, even setting up bridge-like extensions.

The group claimed that the ants appeared to modulate these shape adjustments by a system of “treadmilling.” As Wagner stated, every ant raft is produced up of two levels. On the bottom, you can obtain “structural” ants who cling limited to each individual other and make up the foundation. Previously mentioned them are a 2nd layer of ants who wander around freely on best of their fellow colony-users.

About a interval of hrs, ants from the base may well crawl up to the top, whilst free of charge-roaming ants will drop down to come to be element of the structural layer.

“The full thing is like a donut-shaped treadmill,” Wagner reported.

Bridge to basic safety

In the new examine, he and Vernerey required to explore what would make that treadmill go spherical.

To do that, the crew developed a sequence of versions that, essentially, turned an ant raft into a difficult game of checkers. The researchers programmed roughly 2,000 round particles, or “agents,” to stand in for the ants. These brokers couldn’t make decisions for themselves, but they did adhere to a straightforward established of policies: The faux ants, for illustration, did not like bumping into their neighbors, and they tried out to stay away from slipping into the water.

When they permit the game engage in out, Wagner and Vernerey found their simulated ant rafts behaved a great deal like the genuine matters.

In particular, the staff was able to tune how lively the agents in their simulations were: Had been the individual ants gradual and lazy, or did they stroll all-around a lot? The much more the ants walked, the a lot more very likely they had been to type lengthy extensions that trapped out from the raft—a little bit like men and women funneling towards an exit in a crowded stadium.

“The ants at the ideas of these protrusions almost get pushed off of the edge into the drinking water, which prospects to a runaway effect,” he stated.

Wagner suspects hearth ants use these extensions to experience close to their environments, looking for logs or other bits of dry land.

The scientists nevertheless have a great deal to master about ant rafts: What helps make ants in the genuine environment, for case in point, choose to change from sedate to lazy? But, for now, Vernerey states engineers could learn a issue or two from fire ants.

“Our perform on fire ants will, ideally, help us comprehend how straightforward regulations can be programmed, this sort of as through algorithms dictating how robots interact with many others, to attain a properly-qualified and clever swarm reaction,” he claimed.

Supply: College of Colorado Boulder, by Daniel Strain.


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