Characterisation of cuticular nanostructures on surfaces of insects by Atomic Force Microscopy - 'mining' evolution for smart structures

The optical properties of insect nano-structures have been extensively studied. In particular, nano-scale ordered arrays have been reported from studies of the corneal surfaces of some insects and of insect wings showing anti-reflective properties. These arrays have been ascribed to evolutionary adaptation and survival value arising from increased visual capacity and better camouflage against predators. In this study we show that the Atomic Force Microscope (AFM) can effectively reveal and quantify the three dimensional structures of nano-arrays on moth eyes and cicada wings. It is also shown that the arrays present an ideal surface for in situ characterisation of the AFM probe/tip. In addition, a new structure is presented which has been discovered on a termite wing. The structure is similar to that found on the cicada wing, but has a much larger 'lattice parameter' for the ordered array. The function(s) of the array is unknown at present. It could be effective as an anti-reflective coating, but would then be active in the infra-red region of the light spectrum. Alternatively, it may confer evolutionary advantage by virtue of its mechanical strength, or it may improve the aerodynamics of flying. The study demonstrates that natural selection may be a rich source of 'smart' structures.