Natures wonders: fire ant raft dynamics (Introduction)

by David Turell , Tuesday, January 09, 2024, 19:47 (317 days ago) @ David Turell

Don't flatten when stretched:

https://www.newscientist.com/article/2411139-fire-ants-form-rafts-that-have-weird-prope...

"When their nest is flooded, red imported fire ants (Solenopsis invicta) can survive by linking their bodies together to form a floating raft. Past research has suggested that physics plays an important role in the creation of these rafts. Small objects on the surface of a fluid tend to be pushed together by the forces of surface tension, which give the ants an opportunity to grab onto one another. This phenomenon is known as the Cheerios effect, after the way pieces of breakfast cereal clump together as they float in milk.

"But Chung-Hao Chen at National Tsing Hua University in Taiwan and his colleagues suspected that the Cheerios effect isn’t the only factor that explains why fire ants form rafts. This is because some other species of ant, such as Monomorium chinense, which is local to Taiwan, do not form rafts on water – even though the Cheerios effect should push them together in the same way.

"To explore how ant rafts could form without this effect, the researchers put about 500 fire ants on a dry vibrating plate and then shook them either vertically or horizontally.

"After about 5 seconds of vertical shaking, the fire ants clung together to form a ball-like structure. Being shaken horizontally caused them to make a flat, pancake-like structure in just 3 seconds. The M. chinense ants did not cling together to form any structures when shaken.

"Tzay-Ming Hong at National Tsing Hua University, who also worked on the project, says the experiment shows fire ants don’t rely only on the Cheerios effect to come together. Instead, the insects might be linking up by releasing chemicals called pheromones, which “intoxicate” them into intertwining. (my bold)

"The researchers also uncovered new information about the physical properties of ant rafts. For instance, they discovered that a raft is able to withstand being stretched horizontally without becoming much thinner vertically. This highlights the importance of the structure being made of living creatures that can move around and constantly correct its shape, says David Hu at the Georgia Institute of Technology, who wasn’t involved in the research."

Comment: the resistance to flattening means the ants have figured out the best shape for floating. My bold shows the probable mechanism for individual ant responses, which are always the same