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TERMITES – STRUCTURAL ENGINEERS AND WATER MANAGERS

Australian termite researchers have investigated how termites’ clay-building behaviour is determined by their assessment of the environment around them.

For termite professionals, it never ceases to amaze as to how buildings “absolutely smashed” by termites do not collapse. It turns out that termites are pretty good structural engineers, using clay and moisture to manage structural integrity whilst eating as much of the wood as possible.

Over the past couple of years, a team including Sebastian Oberst, Michael Lenz, Joseph Lai and Theodore Evans have unravelled how termites utilise clay and moisture to exploit foraging resources.

Much of their work, both in the laboratory and in the field, has utilised an experimental setup whereby small pieces of wood were placed in between two concrete pavers (see images, right). To create a situation where the wood was under load, the small pieces of wood took all the weight of the upper paver. To create a situation where the wood was not under load (yet in a similar setup to the loaded situation), metal supports were placed in between the pavers to take the weight of the upper paver.

Focusing on the activities of Coptotermes acinaciformis, earlier experiments by the team demonstrated that foraging termites utilise clay in two different ways, depending on whether or not the wood is under load.1

When exploiting unloaded wood, which would be analogous to a piece of wood lying on the surface of the ground, termites will build a thin layer of clay sheeting less than one millimetre thick over the surface of the wood (main picture, above). Such sheeting provides protection from predators and from desiccation.

However, when exploiting wood under load, termites create load-bearing clay walls, typically greater than ten millimetres thick. Interestingly the amount of clay used to support the exploitation of wood under load increases over time – as more of the wood is eaten, the amount of clay used for structural support increases.

The experiments demonstrated that termites preferred unloaded wood to wood under load. This is perhaps not a surprise as such a food resource could be exploited quickly without the energy expenditure needed to build structural clay walls. Anecdotally, termite infestations in buildings appear to follow a similar pattern, with the non-structural timbers attacked during the early stages of an infestation.

The researchers hypothesised that the ability to distinguish whether a wood is under load or not could be achieved through acoustic or vibrational characteristics.

In the field, termites will generally exploit a food resource, such as a dead tree, from the ground up. From an evolutionary point of view, it makes sense that when exploiting such a resource, termites have developed behaviours that prevent the tree’s collapse during foraging to avoid the death of foraging termites.

With termites having the ability to transport water to feeding sites to exploit a food source, the team’s latest research has focused on how termites might use water during the exploitation of food resources.2

Being prone to desiccation, termites will often seek out water and it is generally assumed that termites will prefer wood with a higher moisture content, with moisture levels of around 50% often triggering extensive foraging. The results of their latest study confirm that this was indeed the case for unloaded wood, with termites preferring moist wood to dry wood, and eating the wood without building any clay sheeting. In contrast, they moistened dry wood after wrapping it in a layer of clay.

However, for wood under load is was observed that the foraging termites kept the moisture at a significantly lower level than in unloaded wood. It is hypothesised that the termites keep wood under load drier to provide higher structural stability. This represents a compromise for the termites as the drier wood is harder to forage on. However, presumably by maintaining the structural integrity for an extended period it allows the termites to access a long term, high value food resource, off-setting the fine efficiency of foraging on a drier food source.

It seems that termites really are one of nature’s remarkable engineers, capable of assessing the size and structure of food resources and using clay and water to modify the food resource for optimal foraging.

1 Oberst, Sebastian and Lai, Joseph and Evans, Theodore. (2016). Termites utilise clay to build structural supports and so increase foraging resources. Scientific Reports. 6.10.1038/srep20990.

2 Oberst, Sebastian and Lenz, Michael and Lai, Joseph & Evans, Theodore. (2019). Termites manipulate moisture content of wood to maximize foraging resources. Biology letters. 15. 20180505. 10.1098/rsbl.2019.0365.