Post by lepidofrance on Sept 8, 2013 5:48:32 GMT -8
"It seems not only the green eyes of butterflies fade when they are mounted, I believe many moth specimens with a green colour fade with time."
Most of the green butterflies (at least those I have in my drawers) show a fadishing green along time : Graphium sarpedon, G. agamemnon, G. policenes, and others green Graphium, Philaethria dido, Metamorpha selenes, and so on. Nevertheless, it's quite different with green Ornithoptera.
Who can explain this ? Is there a chemical difference between these greens ? Or physical (something alike with the Morphos blue) ?
As far I know, the Teinopalpus sp. don't fade (I have not enough Teinopalpus since a long time to get an idea !).
The green in Graphium is of chemical nature. As far as I can see the main compound is sarpedobilin which is a blue-green bile pigment. As every chemical compound it can decompose under the influence of heat and light.
The green in Ornithoptera is a physical, structural color. The structure of the scale will only reflect the green light t a certain wavelength. As the structure of the scales does not alter the color will never change.
You can test if a scale has structural or chemical color by either looking with an angle towards the butterfly. Some structural colors, but not all, are angle dependent. Another method is to put acetone on the scales. If the color is made by ridges or grates the color will shift as acetone has a higher refractive index. Please keep in mind that not every structural color can be identified by this. Some structural colors are made by hollow spheres inside the scale. Very often this results in white color. Furthermore some scales may have both chemical pigments and a physical grating structure.
How butterflies get their color is an interesting topic which is so complicated that you can write and read whole books about it. I am currently reading the works of H. Nijhout.
Last Edit: Sept 8, 2013 6:15:12 GMT -8 by nomihoudai
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Post by lepidofrance on Oct 13, 2013 12:17:26 GMT -8
The green eyes of C. croceus : a butterfly very common right now (Sept. & Oct. 2013) in France : a true invasion. For example : yesterday, despite the very cold weather (about 8°C around 1 PM), two minutes after the first sun glimpse (around 4 PM), a dozen of croceus flying in the garden !