As far as I know, all of the "metallic" finishes found on insects are due to many-layer interference effects. See HERE in Google Books for section 25.2 Physical Colors, starting on page 657 of "The insects: structure and function" by R. F. Chapman. An interesting snippet begins on page 659:DQE wrote:I'm trying to think of specific unique cases of interest, and jewel wasps come to mind, although they may have highly dimpled surfaces. I can also visualize small, very shiny, metallic-appearing wasps but can't recall their names at the moment.
In other words, how much do the widely varying surfaces of **nominally smooth-surfaced** bugs affect the use of on-camera polarizers to reduce and manage excessive surface reflections of flash-exposed photos? Along the same line of thought, are there unique bug's surfaces that involve thin-film interference effects or real metal surfaces, thereby reducing the benefits of on-camera polarization?
Your particular choice of the jewel wasp makes a good test subject, because I still have available the specimen pictured HERE. I tested it just now with polarizing filters, and discovered that its brightly colored cuticle has a very interesting mix of characteristics. When illuminated by non-polarized glancing light near Brewster's angle, the reflections become highly polarized as one would expect for an organic material. However, when illuminated from the front, the cuticle acts more like blue metal. If the front illumination is non-polarized , the shiny blue cuticle adds no obvious polarization of its own, and when illuminated by polarized light, it preserves that polarization. This means that using crossed polarizers to kill specular reflections is a complete disaster. When arranged to eliminate the unpleasant reflections of my tiny fiber optic bundle, crossed polarizers made the whole wasp go black!The brightness of the reflected color increases with the number of reflecting surfaces. In Morpho species, there are only eight to 12 horizontal mullions, and similar numbers of layers are present in the cuticles of buprestid beetles. Only a small percentage of light, less than 40%, is reflected. By contrast, the metallic gold or silver cuticles of pupae of danaid butterflies have over 200 reflecting layers and almost 80% of the incident light over a broad band of wavelengths is reflected. Amongst scarab beetles, reflectivity is enhanced by large amounts of uric acid in the reflecting layers.