Termites engineer the ‘bricks’ for their mounds from very fine soil particles. These less-than-half-millimetre-wide spherical pieces called boluses are crafted using moisture and materials (ideally granular, organic, with an affinity for water) available in their surroundings, shows a new study. This information could be used to predict the distribution of termites at local and regional levels.
Termites – eusocial insects which live in colonies with wingless workers undertaking most of the labour – build nests or mounds known to alter soil properties and enhance vegetation growth in arid regions, helping stabilise ecosystems. Little is known about how termites construct these mounds. Scientists at the Indian Institute of Science, Bengaluru, studied mound construction, and how the mound-building, fungus-farming termite Odontotermes obesus chooses material for boluses. In lab experiments, they offered moistened tissue paper as a water source, and various materials – including sand, stainless steel and so on– to see which ones termites preferred. They found that workers did not necessarily prefer familiar material like red soil, but used any type of material as long as it was granular enough and had enough moisture content to aid the process of cementation. Only workers created boluses; and boluses of the larger major workers were 3.7 times larger in volume than thhose of minor workers.
Strategic packing
The scientists made an opening in a mound and recorded how termites repaired it by analysing the video frame-by-frame. They found minor workers strategically placed their smaller boluses in between the boluses crafted by major workers, to optimally 'pack' the area. The study also shows that moisture was crucial: termites could not walk on surfaces that had too much moisture; if moisture was too low, they could not use their saliva to craft boluses.
“Our study shows that soil type and access to ground water is vital for building mounds,” says ecologist Renee Borges in whose laboratory the study was conducted.
“In the Western Ghats, many communities use mounds as an indication of groundwater presence. Mounds also serve as nuclei: more vegetation in some areas is facilitated by these ecosystem engineers. We have at least ten termite species in Bengaluru alone, but we don’t know the distribution of several species – termites are poorly studied. We hope our study will serve as a benchmark to study species in other areas.”
