Brilliant iridescent colouring in male butter£ies enables long-range conspeci¢c communication and it has long been accepted that microstructures, rather than pigments, are responsible for this coloration. Few studies, however, explicitly relate the intra-scale microstructures to overall butter£y visibility, both in terms of re£ected and transmitted intensities and viewing angles.Using a focused-laser technique, we investigated the absolute re£ectivity and transmissivity associated with the single-scale microstructures of two species of Morpho butter£y and the mechanisms behind their remarkable wide-angle visibility. Measurements indicate that certain Morpho microstructures re£ect up to 75% of the incident blue light over an angle range of greater than 1008 in one plane and 158 in the other.We show that incorporation of a second layer of more transparent scales, above a layer of highly iridescent scales, leads to very strong di¡raction, and we suggest this e¡ect acts to increase further the angle range over which incident light is re£ected.Measurements using index-matching techniques yield the complex refractive index of the cuticle material comprising the single-scale microstructure to be n (1.56 AE 0.01) + (0.06 AE 0.01)i. This ¢gure is required for theoretical modelling of such microstructure systems.
With 1 plate and 12 figures in the text) r Coupled investigations of insect wing movements and detailed wing morphology are in progress, and some functional principles underlying wing design are emerging. High speed cine and still photography and stroboscopy indicate that most wings undergo orderly deformation in flight. Common patterns are described and their significance discussed in the light of recent aerodynamic studies.Many aspects of wing morphology-venational features, relief, thickened areas, flexionlines and vein fractures-may be related to the control of three-dimensional shape while beating. It is usually possible to distinguish areas specialized for deformability, and for support and the limiting of deformation. Some structural adaptations for these roles are described and illustrated.
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