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Watch As Fire Ants Build A "Treadmilling" Raft To Escape Flood Water

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Rachael Funnell

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clockJul 5 2021, 11:30 UTC
Watch As Fire Ants Build A "Treadmilling" Raft To Escape Flood Water

By spontaneously forming branches from the raft the ants increase their chances of finding a means of escape. Image courtesy of Vernerey Research Group, University of Colorado, Boulder

Looking at ants and cells, you might struggle to see much in the way of similarities between the two other than that they are both small and often exist in large numbers. However, new research has found that under the right circumstances, some ants actually explore their environment in a way that mirrors cell movement. Those “right circumstances” are floods, which fire ants are usually able to survive thanks to their impressive raft forming skills. That fire ants can form these floating islands by linking their bodies to form agregations has been recognized for some time, but for the first time new research has captured these ant aggregates “treadmilling” their way to safety.

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The research, published in the Journal of the Royal Society Interface, focused on fire ants (Solenopsis invicta), so named for the nasty burning sensation experienced by those unlucky enough to be bitten by one. The average colony can contain anywhere from 100,000 to 500,000 ants and these individuals can band together when exposed to flooded environments and form a buoyant mass. The researchers on the new study wanted to observe in greater detail what was going on in these rafts, so they left some ants to bob about as a docked raft for a few hours and then reviewed the footage.


The videos revealed that a fire ant raft consists of layers, with a structural network of interconnected ants supporting a top layer of freely moving ants. The movement of structural ants to the free ant layer and vice versa means the raft isn’t stationary but perpetually contracting as everyone on board shuffles about. Furthermore, asymmetries at the raft’s edge emerge as free ants join hands with their structural ant brethren, and these asymmetries can lead to the establishment of tether-like protrusions. While their emergence is spontaneous, they facilitate exploration and have the potential to give rise to a means of escape for the stranded fire ants.

While a happy accident for ants wanting to flee a flooded environment, the researchers observed that after a few hours the islands would essentially hunker down, forming a tighter ball around the rod within the tank to which they were anchored. They theorize that the waxing and waning exploratory behavior is probably an energetically expensive one and given that ants have been reported to stay marooned on their rafts for months it probably pays to conserve energy. Exactly how these “group decisions” are established, however, remains unclear.

“Whether this is a mutual decision by the ants, or the result of tired individuals independently deciding to rest isn’t really clear, but this is the type of question that fascinates us,” Professor Franck J Vernerey, Ph.D. of the Department of Mechanical Engineering at the University of Colorado, Boulder told IFLScience. “How are these cooperative behaviors happening? Are they from some centralized decision making process that requires communication, or do they emerge from the individual decisions of these simple units?”


Whatever the process involved, it seems to be a repeating theme in nature as Vernerey and colleagues recognized similarities between the ants’ exploration and the way single cells move. By speeding up the footage, they were able to see that the structural and free ants were always shifting, recycling themselves in what Vernerey describes as a “2D, self-healing conveyer belt.” This, he says, is akin to what the cytoskeletons of cell walls do to facilitate locomotion.

“We adopted the term ‘treadmilling’ from that field. It’s fascinating because while cells and ants exist at very different length scales, they’re both comprised of relatively simple units that achieve this sort of collective intelligence. In both cases, treadmilling allows these living systems to probe and explore their environments, and then move as a whole. Nature evolved these similar mechanisms for the same purpose across two disparate length scales," Vernerey explained.

“I think the notion that biological systems evolve such similar ways of achieving functional tasks is remarkable and rightly deserves a lot of attention from the scientific community. Three+ billion years of raw trial and error has given nature a big head start on coming up with innovative solutions to problems, and when similar solutions emerge more than once at different length scales, we should probably pay attention.”


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