Reflectance Causes White Color

a white butterfly with a black spot on a wing sits on a purple flower against a blurry background

Biological Strategy

Cabbage white butterfly

AskNature Team

Image: PurpleOwl / Pixabay / Free non-commercial use

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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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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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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The wings of the cabbage butterfly are white due to longitudinal ridges and cross-ribs studded with ovoid beads.

Image: Didier /

Image: Dendroica cerulea /

“The small white, P. [Pieris] rapae, offers an interesting example of the biology of wing coloration. Both sexes of this butterfly species are rather featureless for human eyes, except for slight differences in the black spots, small wing areas where the wing scales contain melanin. The white color is caused by strongly scattering structures in the wing scales (Stavenga et al., 2004). The reflectance is only high above 450 nm, but it is minor below 400 nm, because the scales of male P. rapae crucivora contain a substantial amount of UV-absorbing pteridins.” (Stavenga and Arikawa 2006:314)

“Fig. 7. Coloration of pierid butterflies…(b) The wing scales are marked by longitudinal ridges and cross-ribs. (c) The cross-ribs are studded with ovoid beads…(d) The wing scales strongly scatter, but due to pteridin , which strongly absorbs in the UV, the reflectance is low in the UV.” (Stavenga and Arikawa 2006:315)

Last Updated August 18, 2016

References

Journal article

Evolution of color and vision of butterflies

Arthropod Structure & Development | 13/12/2006 | Doekele G. Stavenga, Kentaro Arikawa

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Reference

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