The Emerald-patched Cattleheart

(Perides Sesostris)

The Emerald-patched Cattleheart butterfly generates its green color by structures that fall into the type III category of scales. The picture below is an electron microscope image of a broken wing scale.
The lower layer is the photonic crystal structure that we are interested in.  This structure consists of cuticle (the white color) with arrays of air holes (the dark spots).  If you look closely you can see the holes in the center of the image are arranged differently from those in the bottom right.  The second image below shows this structure with the top layer removed.  This top layer does not contribute to the apparent color of the butterfly.  Notice that the uneven areas have different hole patterns depending on how the scale fractured.  

Take out the the white cube shaped model with holes in  it. This structure is called a gyroid. Compare it to the the image to the left. Is it similar? How many different ways can you hold it and get different hole patterns?

The next picture shows a much larger section of the butterfly scale.  This shows that the scales are made up of at least 8 different orientations of the same gyroid structure. 
These different orientations average about 3.7 um [29.7 S/D] wide.  Each of these different orientations produce a color that is independent of the viewing angle.


The scale bar is 1 um long.     Ghiradella (1994)

Vukusic (2003)