When bile is beautiful
In my SUPPOSE WE science fiction novel, the Chief Science Officer, Gaston, is enamoured by an alien butterfly he calls Papillon. The creature looks like a butterfly with the size of a Red Admiral, but it really is in a symbiotic connection with its owner, a Keplerian being. A kind of information gatherer. So, not a butterfly at all in spite of its “flying crooked” flight and lack of sound. In the story Papillon is a purple colour which made me wonder about real butterfly colours in general.
Butterflies are of the order Lepidoptera because Lepido means scales and Ptera means wings. (remember Pterodactyl?) Looked at closely, butterfly wings are scaled, like many insects. I’ve always assumed their colours come from the way the microscopic (nano) scale shapes absorb and reflect light coupled with pigment – if any- they derived as larva when they ate plants or as the winged adult which only drinks nectar or sap. This is mostly the case. However, they can add a more interesting element into their wing colours. Bile!
In humans bile is formed by the liver to aid the breakdown of fats. It’s stored in the gall bladder. Why butterflies need bile when they don’t eat fats is a puzzle though all creatures make some fats eg cholesterol that need breaking down at some point
Carotenoids especially lutein are yellow and red pigments, eaten by caterpillars and is mostly responsible for their green colour (wait for it). Lutein is what makes egg yolk yellow) You might think their eating the plant chlorophyll does that but apparently not so much. Something blue is needed to mix with the yellow lutein and blue pigments from bile.
So the colours of butterflies often come from a mix of chemicals they take in from plant juices, their scale nano geometry and poop juice, or bile. Lovely.
Gaston loves Papillon so much that when he is separated from its Kep owner he is presented with his own Papillon clone, which is green. Now there are few green butterflies on Earth. The Green Hairstreak is one in Europe and the beautiful Malachite butterfly in the Americas. It’s good that I haven’t mentioned the nearly invisible Glasswing butterfly or I’d have to explain how its wings are transparent! Oops. I’ll let you think about that one.
A link to more explanation of butterfly colouring with some stunning images is at the link below:–
To engage with Gaston’s experience of Papillon, read SUPPOSE WE and its sequels. Paperback and Kindle plus Kindle Unlimited.