Prepona praeneste buckleyana (male) in human visible light (left) and UV (right). |
Butterflies are known for their
brilliant display colors, but did you know that these colors are even more complex
than what we see? The tiny scales on butterfly wings are capable of reflecting
ultraviolet light (UV), and their eyes are capable of detecting it with UV
sensitive opsins.
By taking photographs of UV light, we can see
some of these hidden patterns, and try to interpret the colors they might perceive. The image at the top of this post, for example, reveals a UV pattern
across the middle portion of the wing. The picture below demonstrates how this
UV can contribute to colors as the butterflies perceive them. The forewing is
orange to our eyes, but it has bright UV reflectance as well, so this color
would better be described as a UV-orange (although I’m sure UV sensitive
organisms would come up with some better names
if they could). The hindwing, however, is just yellow as we know it, with no UV.
Hebomoia leucippus in human visible light (left) and UV (right). |
I’d also like to clarify that the
UV colors of butterflies are the result of UV reflectance, which is something entirely
different than fluorescence (where UV light seems to make an object
glow, like clothes under a blacklight). I’ll make another post about
fluorescence in the future, as there are some very interesting examples of
biofluorescence in nature.
Want to learn more about how these
colors are made? Butterfly scales are capable of producing structural coloration through
interference mechanisms such as diffraction gratings. These typically reflect short wavelength light, such as the blue of Blue Morphos
and UV in the butterflies above. The wing membrane below the scales may contain
various pigments which also contribute to the color of the wing, and the interaction
of structures and pigments increases the butterfly’s potential color gamut.
SmarterEveryDay made a very interesting video about butterfly structural
coloration, which I recommend watching.