Abstract
Animal constructions such as termite mounds have received scrutiny by architects, structural engineers, soil scientists and behavioural ecologists but their basic building blocks remain uncharacterized and the criteria used for material selection unexplored. By conducting controlled experiments on Odontotermes obesus termites, we characterize the building blocks of termite mounds and determine the key elements defining material choice and usage by these accomplished engineers. Using biocement and a self-organized process, termites fabricate, transport and assemble spherical unitary structures called boluses that have a bimodal size distribution, achieving an optimal packing solution for mound construction. Granular, hydrophilic, osmotically inactive, non-hygroscopic materials with surface roughness, rigidity and containing organic matter are the easiest to handle and are crucial determinants of mass transfer during mound construction. We suggest that these properties, along with optimal moisture availability, are important predictors of the global geographic distribution of termites.
Highlights
Animal constructions such as termite mounds have received scrutiny by architects, structural engineers, soil scientists and behavioural ecologists but their basic building blocks remain uncharacterized and the criteria used for material selection unexplored
Termites agglomerate the finer fraction of soil particles into unitary structures called boluses, which they employ for mound construction[15]
We present data that have bearing on all three construction stages and, using our results taken together, we define the crucial determinants of mound construction by termites
Summary
Animal constructions such as termite mounds have received scrutiny by architects, structural engineers, soil scientists and behavioural ecologists but their basic building blocks remain uncharacterized and the criteria used for material selection unexplored. Hydrophilic, osmotically inactive, non-hygroscopic materials with surface roughness, rigidity and containing organic matter are the easiest to handle and are crucial determinants of mass transfer during mound construction We suggest that these properties, along with optimal moisture availability, are important predictors of the global geographic distribution of termites. We found that only major and minor worker castes of termites (not soldiers) agglomerated the locally available red soil into boluses, which are densely compacted structures with a range of soil particle sizes (Fig. 1; see Supplementary Figs S2 and S3a; Supplementary Video S1) These boluses are the basic building blocks of construction and are analogous to bricks used in human construction
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