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Biophysics of the insect liquid-crystal carapace

Where is the anisotropy in the organization of the constituents of the tessellated carapace of the scarab? What are the related structural and optical properties? For which biological functions? What source of inspiration for novel advanced optical materials? These questions motivate our investigations from the cholesteric cuticle made of chitin fibers to the ultimate wax layer, which is intriguing.

Contact : Michel Mitov, mitov[AT]cemes.fr

Insect carapaces as photonic structures

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Cholesteric liquid crystals are omnipresent in living matter under both in vivo and in vitro conditions and address the major types of molecules essential to life. In many insect carapaces, chitin fibers organize into a cholesteric structure which confers to insects iridescent colors producing spectacular visual displays. A great number of insects utilize tessellated carapaces, containing arrays in the form of bumps, pits, stripes, pixels or other patterns. Understanding the sense of these physical variations may help to understand the role of optical information in the evolution of insects. It may also inspire the design of novel biomimetic materials to be used in nanophotonics, micro-optics, thermal regulation or camouflage.

We show that the optical properties of the two-band carapace of the scarab beetle Chrysina gloriosa come from twisted structures with a variable orientation of the helical axis coupled to a pitch gradient. Over the visible and near IR spectra, polygonal cells in tessellated green stripes behave as multiwavelength selective micro-mirrors and the silver stripes as non-textured specular broadband mirrors. The conclusions of the literature supporting the similarity of the structures and optical behaviors for synthetic and biological materials have to be revised. Biomimetic materials could be used in the domain of wavelength-selective light modulators and packet switching for the routing of optical information.


  • G. Agez, C. Bayon and M. Mitov, Multiwavelength micromirrors in the cuticle of scarab beetle Chrysina gloriosa, Acta Biomater., 48, 357-367 (2017).
  • M. Mitov, Cholesteric Liquid Crystals in Living Matter, Soft Matter, 13, 4176-4209 (2017).


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 Wax layer in insect cuticle

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Studies on wax layer in insect cuticles have mainly focused on its chemical composition revealing complex mixtures of lipids. In the absence of information on its physical organization, the wax layer has been considered isotropic. However we show in the case of the scarab beetle Chrysina gloriosa that it may exhibit an internal anisotropic layered texture with a mean periodicity of 28 nm. Re-examining past investigations of cuticular structures with a major focus on the wax seems therefore to be necessary. It could give the impetus to search for anisotropic textures in the wax layer of other scarab beetles, insects or arthropods in general. 

Reference paper: M. Mitov, V. Soldan and S. Balor, Observation of an anisotropic texture inside the wax layer of insect cuticle, Arthropod Structure & Development, 47, 622-626 (2018).