Fire ant rafts form because of the Cheerios effect, study concludes

Fire ants are fascinating as an example of collective behavior, even though they are a problem in the south. Some fire ants are 888-609- 888-609- 888-609- 888-609- 888-609- Pack enough of them close together and they act like a single unit. They can form rafts, arrange themselves into towers, and even pour them from a teapot.

"Aggregated, they can almost be thought of as a material, known as 'active matter,'" said Hungtang Ko, who began studying these fascinating creatures as a Georgia Tech graduate student in the year 2000. He has been stung many times. Two recent papers investigated the physics of fire ant rafts. The journal B&B investigated how fire ant rafts behave in flowing water.

The mechanism by which fire ants come together to form the rafts was explored in the second article.

A single ant has a lot of hydrophobia. The property is increased when they link together. The ants gather up any eggs, make their way to the surface via their tunnels in the nest, and as the flood waters rise, they bite on each other's bodies with their mandibles and claws. The ants are able to do this in less than a minute. The structure of the ant raft can stay stable even for months at a time if it loses an ant.

Fire ants were able to sense changes in forces on their raft. The ants were able to adapt their behavior to preserve the stability of the raft. The ant rafts will spin when a paddle moves through the water. The raft can be broken apart due to the extra force of the vortices. The changes in the forces acting on the raft are very small. The ants can sense small shifts in their body.

There are a few simple rules that seem to govern how floating rafts of fire ants contract and expand over time. At the time, we reported that the structures would become dense with ants. Sometimes the ants would use the extensions to escape the containers.

The rafts are made up of two separate layers. The stable base of the raft is made up of ants on the bottomlayer. The ants on the upper layer are free to move on top of their brethren on the bottom layer. Sometimes ants move from the bottom to the top in a cycle similar to a treadmill.

The Boulder study looked at the broad collective dynamics rather than interactions between individual ants. Ko told Ars that there are thousands and thousands of ants in the wild, but nobody really knows how a pair of ants interact with each other, and how that affects the stability of the raft.

It can be an issue with large rafts. Ko wanted to gain more control over his experiments and study how ants adapt to different situations in water. The ants change the shape of the raft to reduce drag. "Maybe it takes less force to hold onto the vegetation than it would be if they stuck with the original pancake shape," said Ko.