Data from: Ridge and crossrib height of butterfly wing scales is a toolbox for structural color diversity

The brightest and most vivid colors of butterflies usually originate from
light reflecting off the cuticular scales that cover the wing membrane.
These scales have an intricate architecture that consists of an upper
layer, a grid of longitudinal ridges and transverse crossribs, connected
to a lower lamina by pillars called trabeculae. Whereas the role of the
lower lamina as a reflector has been well documented in simpler scales,
this study unveils the role of the scales’ upper surface in generating or
fine-tuning hue, brightness, and saturation. In the nymphalid Bicyclus
anynana, we showed that changes in ridge and trabecula heights accompanied
changes in the hue of scales produced via artificial selection. We further
found that this correlation between ridge height and hue can be
generalized to 40 scale types from 35 species across butterfly families.
By combining focused ion beam milling, microspectrophotometry, and optical
modelling, we found that modifying the ridge height is sufficient to
change ridge hue, notably in Morpho didius, whose blue color was thought
to be generated by lamella protruding from ridges, rather than ridge
height. This study identifies the scale’s upper surface as a toolbox for
structural color diversity in butterflies and proposes a geometrical model
to predict color that unifies species with and without Morpho-type
Christmas-tree ridges.