Pigment Granules Create Colors

an iridescent green teal and orange damselfly rests on a grass

Biological Strategy

Dragonflies and damselflies

AskNature Team

Image: James Wainscoat / Unsplash / Free non-commercial use

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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The bodies of damselflies have brilliant metallic colors derived from structural arrangement of pigment granules.

“The brilliant metallic colours of many Odonata, especially damselflies, derive from the structural arrangement of granules. Pigment in the wings of such species as Agrion virgo is similarly distorted by light to produce resplendent shifting effects of green-blue-purple. In some male dragonflies, as Libellulids, the pale Cambridge blue of the abdomen has a distinctive structural cause since it initially derives from a fine powdery exudation of the epidermal cells, producing an effect like the bloom on a plum: the granules are so small and regularly arranged that they reflect only the pale blue part of the light spectrum and, indeed, often appear almost white.” (Wootton 1984:140)

“The appearance, fine structure and pigment composition of the epidermal chromatophores of mature Austrolestes annulosus (Lestidae) are described and compared with the developing chromatophores of teneral Austrolestes and the mature chromatophores of Diphlebia lestoides (Amphipterygidae) and Ischnura heterosticta
(Caenagrionidae). Mature chromatophores contain masses of near
spherical light-scattering bodies and larger irregularly shaped pigment
vesicles. These effect colour change by migrating in opposite
directions, through a system of interconnecting granular endoplasmic
reticulum tubules. The pigment, a mixture of xanthommatin and
dihydroxanthommatin, has a liquid or gelatinous consistency. Developing
chromatophores of teneral insects lack light-scattering bodies and
well-defined migratory pigment vesicles, but contain irregular masses of
pigment of similar chemical composition.” (Vernon et al. 1974:613)