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Mechanics of fire ant aggregations

Nature Materials volume 15, pages 54–59 (2016)Cite this article

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Abstract

Fire ants link their bodies to form aggregations; these can adopt a variety of structures1,2,3,4, they can drip2 and spread4, or withstand applied loads5,6. Here, by using oscillatory rheology, we show that fire ant aggregations are viscoelastic. We find that, at the lowest ant densities probed and in the linear regime, the elastic and viscous moduli are essentially identical over the spanned frequency range, which highlights the absence of a dominant mode of structural relaxation7. As ant density increases, the elastic modulus rises, which we interpret by alluding to ant crowding and subsequent jamming. When deformed beyond the linear regime, the aggregation flows, exhibiting shear-thinning behaviour with a stress load that is comparable to the maximum load the aggregation can withstand before individual ants are torn apart. Our findings illustrate the rich, collective mechanical behaviour that can arise in aggregations of active, interacting building blocks.

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Figure 1: Liquid-like and solid-like behaviour of fire ant aggregations.
Figure 2: Shear thinning of fire ant aggregations.
Figure 3: Creep behaviour of fire ant aggregations.
Figure 4: Viscoelasticity of fire ant aggregations.
Figure 5: Elastic modulus of fire ant aggregations.

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Acknowledgements

This research is supported by the US Army Research Laboratory and the US Army Research Office Mechanical Sciences Division, Complex Dynamics and Systems Program, under contract numbers W911NF-12-R-0011 and W911NF-14-1-0487. We are also grateful to L. Mahadevan and G. McKinley for useful discussions.

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Authors and Affiliations

  1. School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332, USA

    Michael Tennenbaum & Alberto Fernandez-Nieves

  2. School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, USA

    Zhongyang Liu & David Hu

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  1. Michael Tennenbaum
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Contributions

M.T. and Z.L. performed experiments. M.T., D.H. and A.F.-N. designed experiments. M.T., D.H. and A.F.-N. analysed and interpreted data. M.T., D.H. and A.F.-N. wrote the paper.

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Correspondence to David Hu.

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The authors declare no competing financial interests.

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Tennenbaum, M., Liu, Z., Hu, D. et al. Mechanics of fire ant aggregations. Nature Mater 15, 54–59 (2016). https://doi.org/10.1038/nmat4450

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