Scales Enhance Wing Color

a butterfly with a white body, black wings with blue spots sits on a green plant with a green background

Biological Strategy

Blue triangle butterfly

AskNature Team

Image: William Warby / Flickr / CC BY - Creative Commons Attribution alone

Modify Light/Color

Color in living systems comes from pigments and the interaction of light with surfaces. Color serves many purposes for living systems, such as attracting prey or mates, providing warnings, or protecting through camouflage. To create the effects needed for each purpose, living systems must control the expression or visibility of pigments and the interactions (such as reflectance and refraction) of light. To do so, they have strategies that modify color or light to increase or decrease the color’s position, intensity, opacity, and more. Male hummingbirds, for example, have brightly colored feather patches on their throats; the coloring comes from pigments, structures that refract light, or a combination of the two. When a male hummingbird hovers near a potential mate, it modifies the angle of these feathers to create a bright, colorful display. However, when it needs to mute the colors to reduce conspicuousness, such as to avoid a predator, it modifies the angle again.

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Send Light Signals in the Visible Spectrum

The visible spectrum is the portion of the electromagnetic spectrum that the human eye can detect. Visible light can be thought of in two ways–light as illumination (such as that used by fireflies) and colors that result from light being absorbed or reflected. Living systems use light for a variety of purposes. Sometimes, they use it to make themselves highly visible (like a peacock showing off his brilliant feathers to a potential mate). Other times, they use it to become virtually invisible (like an owl hiding in plain sight when it rests during the day). When a living system sends a light signal, it must create that light or color in an energy- and material-efficient way. Living systems create and enhance color using such strategies as non-toxic pigments, structures that bend and absorb different wavelengths, and chemical processes that create bioluminescence.

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Insects

Class Insecta (“an insect”): Flies, ants, beetles, cockroaches, fleas, dragonflies

Insects are the most abundant arthropods—they make up 90% of the animals in the phylum. They’re found everywhere on earth except the deep ocean, and scientists estimate there are millions of insects not yet described. Most live on land, but many live in freshwater or saltwater marshes for part of their life cycles. Insects have three distinct body sections: a head, which has specialized mouthparts, a thorax, which has jointed legs, and an abdomen. They have well-developed nervous and sensory systems, and are the only invertebrate that can fly, thanks to their lightweight exoskeletons and small size.

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Scales on the ventral side of swordtail butterfly wings enhance blue/green coloring via light reflection and diffusion.

“The wings of the swordtail butterfly Graphium sarpedon nipponum
contain the bile sarpedobilin, which causes blue/green
colored wing patches. Locally the bile pigment is combined with
the strongly blue-absorbing lutein, resulting in green
wing patches and thus improving camouflage. In the dorsal forewings,
the colored patches lack the usual wing scales, but instead
have bristles. We have found that on the ventral side most of
these patches have very transparent scales that enhance, by
reflection, the wing coloration when illuminated from the dorsal
side. These glass scales furthermore create a strongly polarized
iridescence when illuminated by obliquely incident light
from the ventral side, presumably for intraspecific signaling. A
few ventral forewing patches have diffusely scattering, white scales
that also enhance the blue/green wing coloration when observed
from the dorsal side.” (Stavenga et al. 2010:1731)