Brilliant iridescent colouring in male butterflies enables long-range conspecific 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 butterfly visibility, both in terms of reflected and transmitted intensities and viewing angles. Using a focused-laser technique, we investigated the absolute reflectivity and transmissivity associated with the single-scale microstructures of two species of Morpho butterfly and the mechanisms behind their remarkable wide-angle visibility. Measurements indicate that certain Morpho microstructures reflect up to 75% of the incident blue light over an angle range of greater than 100° in one plane and 15° 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 diffraction, and we suggest this effect acts to increase further the angle range over which incident light is reflected. Measurements using index-matching techniques yield the complex refractive index of the cuticle material comprising the single-scale microstructure to be = (1.56 ±0.01) + (0.06 ±0.01)i. This figure is required for theoretical modelling of such microstructure systems.
These references are in PubMed. This may not be the complete list of references from this article.
- Bennett AT, Cuthill IC. Ultraviolet vision in birds: what is its function? Vision Res. 1994 Jun;34(11):1471–1478.
- Bernhard CG, Boëthius J, Gemne G, Struwe G. Eye ultrastructure, colour reception and behaviour. Nature. 1970 May 30;226(5248):865–866.
- Ghiradella H. Structure of butterfly scales: patterning in an insect cuticle. Microsc Res Tech. 1994 Apr 1;27(5):429–438.
- Ghiradella H, Aneshansley D, Eisner T, Silberglied RE, Hinton HE. Ultraviolet reflection of a male butterfly: interference color caused by thin-layer elaboration of wing scales. Science. 1972 Dec 15;178(4066):1214–1217.
- Land MF. The physics and biology of animal reflectors. Prog Biophys Mol Biol. 1972;24:75–106.
- Miller WH, Bernard GD. Butterfly glow. J Ultrastruct Res. 1968 Aug;24(3):286–294.
- Parker AR, Mckenzie DR, Ahyong ST. A unique form of light reflector and the evolution of signalling in Ovalipes (Crustacea: Decapoda: Portunidae) Proc Biol Sci. 1998 May 22;265(1399):861–867.