Natures wonders: ant rafts and towers (Introduction)

by David Turell @, Wednesday, July 12, 2017, 01:11 (1097 days ago) @ David Turell
edited by David Turell, Wednesday, July 12, 2017, 01:22

It is npw sdttled. research has shown that ant rafts and towers are due to automatic activities on the part of each ant:

"The fire ants (Solenopsis invicta), which are found in wetlands, link together to build living rafts to keep the colony afloat during floods. When the water recedes, they cling to exposed plants and form a tower as a temporary shelter until they have a chance to build an underground nest.

"Craig Tovey of Georgia Tech and colleagues set up a camera to study how the ants build such a tower, and accidentally left it rolling for an hour after it was built. Since the tower appeared to be static once built, they thought the footage would be worthless.

"But when a PhD student watched it back at 10 times normal speed, he noticed that the middle of the tower was slowly sinking. “When you speed it up, the ants on the surface are a blur and underneath the blur you can see the slow sinking movement of the tower,” says Tovey.

"After further experiments, they realised that the sinking was due to ants at the bottom moving outwards under the weight of the ants on top. Meanwhile, ants on the outside were perpetually rebuilding the tower by moving towards the top. “The rest of the tower is gradually sinking, while the ants at the top keep building it higher and higher,” says Tovey. “It’s kind of hilarious.”

"The team’s previous research on ant rafts showed how, although no one is in charge and no ant can see the big picture, simple behavioural rules can lead to the creation of a resilient structure. The same rules guide the construction of the tower, with the added limitation of how much weight an ant can support." ( my bold)

Comment: that seems to settle the issue. Individual ant responses due to instinctual individual behaviour builds the structures

Further info:

"But vertical is a relative term. The ants don't position themselves straight up and down like a skyscraper. Instead, the tower gets wider as it grows taller, gradually becoming the same shape as Paris' iconic landmark. The weight of the tower is supported by a wider cross-section at its base, which allows the ants to better distribute their weight.

"'We found that ants can withstand 750 times their body weight without injury, but they seem to be most comfortable supporting three ants on their backs," said Craig Tovey, a co-author of the study and professor in Georgia Tech's Stewart School of Industrial & Systems Engineering. "Any more than three and they'll simply give up, break their holds and walk away."

"Even though the ants evenly distribute their weight as a group, the tower is in constant motion. The column sinks as the insects work, as if the bottom is being melted like butter. The ants slide down, then exit out of tunnels buried in the base. The tower's movement is similar to a slow-motion chocolate fountain in reverse.

"The sinking was confirmed by X-ray videography. The researchers fed some of the ants radioactive food, then threw the colony in an X-ray machine across campus in Professor Dan Goldman's physics lab. Cameras again recorded the critters building a tower. Using time-lapse photography, they watched the radioactive insects walk up the sides, gradually sink to the tower's depths, leave the pile, then continually repeat the process for hours."

Comment: A very solid study. The colony is not one giant brain.

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