New J. Phys. 10 (March 2008) 033014 (14pp) doi: 10.1088/1367-2630/10/3/033014
Diffractive hygrochromic effect in the cuticle of the hercules beetle Dynastes hercules
M Rassart1,3, J-F Colomer1, T Tabarrant2 and J P Vigneron1
1 Laboratoire de Physique du Solide, University of Namur, 61 rue de Bruxelles, 5000 Namur, Belgium
2 Laboratoire de Physique des Matériaux Electroniques, University of Namur, 61 rue de Bruxelles, 5000 Namur, Belgium
3 Author to whom any correspondence should be addressed.
E-mail: marie.rassart@fundp.ac.beAbstract.
The elytra from dry specimens of the hercules beetle, Dynastes hercules appear khaki-green in a dry atmosphere and turn black passively under high humidity levels. New scanning electron images, spectrophotometric measurements and physical modelling are used to unveil the mechanism of this colouration switch. The visible dry-state greenish colouration originates from a widely open porous layer located 3 μm below the cuticle surface. The structure of this layer is three-dimensional, with a network of filamentary strings, arranged in layers parallel to the cuticle surface and stiffening an array of strong cylindrical pillars oriented normal to the surface. Unexpectedly, diffraction plays a significant role in the broadband colouration of the cuticle in the dry state. The backscattering caused by this layer disappears when water infiltrates the structure and weakens the refractive index differences.
Received 14 January 2008
Published 11 March 2008
Setup information is available for
Adobe Acrobat.
EndNote, ProCite ® and Reference Manager ® are registered
trademarks of ISI Researchsoft.
