How do individual insects no bigger than a grain of rice manage to work together to build living towers that hold their structure? It turns out that fire ants may just be following a small set of simple inbuilt rules, and researchers think they have figured out what these might be.
One of these rules seems to be that they always appear to want to fill in the gaps when they find them. If a colony of the ants finds a branch sticking up, they tend to start to form a tower surrounding it. This drive to want to fill in the spaces more often than not means traveling to the top of the structure, adding height. But then it seems to reach a stasis, in which the tower stops growing. New research, however, has found that this structure is anything but in stasis.
After accidentally leaving a video camera filming the ants building towers rolling for an hour after the structure was built, scientists found out that even though at a glance the finished tower looks stable, it is actually a dynamic, constantly moving thing as the ants flow from the bottom to the top in a continuous cycle. This means that even though it might be constantly sinking, it is also constantly being added to.
To confirm what was going on, they then fed the colony some radioactive food, before sticking them in an X-ray machine and producing a time-lapse film. This enabled them to see how the ants were moving not only on the outside of the structure, but also deep within it. They could sit and watch as the ants continued this behavior for hours on end.
It seems that in addition to their desire to fill in the gaps, they also have a weight limit to what they can cope with. “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,” explained Craig Tovey, a co-author of the study published in the Royal Society Open Science. “Any more than three and they’ll simply give up, break their holds and walk away.”
It seems that this basic rule, coupled with the drive to fill in the spaces they see, is behind the constant state of flux seen when the ants build their towers. As the weight of the ants above them gets too heavy, they move out from the bottom, and then crawl back up to the top where they rebuild the structure.