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.

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Microstructured metallic devices will play a vital role in the continuing search to manipulate the passage of electromagnetic radiation relevant to optical, microwave, and communication technologies. Here, we investigate the electromagnetic response of a completely novel and ultrathin ( wavelength) structure within which is buried a metal-clad waveguiding layer (''core'') of subwavelength width. By removing metal from the core cladding to form a periodic array of slits, radiation is coupled into a standing wave within the layer and the structure resonantly absorbs or transmits radiation of wavelength more than 100 times its thickness. Additionally, such structures display the truly remarkable capability of compressing half of the standing-wave wavelength into a fraction of the expected distance.

The wing-scale microstructures associated with two species of Papilio butterfly are described and characterized. Despite close similarities in their structures, they do not exhibit analogous optical effects. With Papilio palinurus, deep modulations in its multilayering create bicolor reflectivity with strong polarization effects, and this leads to additive color mixing in certain visual systems. In contrast to this, Papilio ulysses features shallow multilayer modulation that produces monocolor reflectivity without significant polarization effects.

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