Moths, often perceived as the more subdued relatives of butterflies, display an astonishing array of colors and patterns. Their coloration serves various functions, from the deep browns and blacks of nocturnal species to vibrant yellows, greens, and iridescent blues. This prompts many to wonder if these creatures can actively change their colors, delving into the biology behind their appearance and environmental interactions.
How Moths Display Color
Moth coloration arises from two primary mechanisms: pigmentary and structural colors, sometimes in combination. Pigmentary colors are produced by chemical compounds (pigments) absorbed or manufactured by the moth’s body. These pigments are then deposited within the tiny, overlapping scales that cover a moth’s wings and body.
Melanins, for example, are common pigments responsible for shades of black, brown, and gray. Pterins produce yellow and red hues, while carotenoids contribute to yellow, orange, and red colors. These pigments absorb certain wavelengths of light and reflect others, resulting in the colors we perceive.
Structural colors, in contrast, result from the physical interaction of light with the microscopic structures of the moth’s scales. These scales possess intricate architectures, such as ridges, lamellae, or diffraction gratings, precisely sized to interfere with light waves. When light strikes these structures, specific wavelengths are reflected or scattered, producing vivid, iridescent or metallic colors like blues, greens, and purples. The appearance of structural colors can shift dramatically depending on the viewing angle, creating a shimmering effect. This is seen in moths like the sunset moth, where black pigment is present, but other colors are created structurally by different thicknesses of chitin and air within the scales.
The Question of Color Change
Adult moths do not possess the physiological ability to significantly change their color after emerging from their pupal stage. Once the scales on their wings and body are formed, their colors are fixed. Unlike animals such as chameleons, which actively adjust skin coloration using specialized cells, a moth’s adult form lacks such dynamic mechanisms.
This differs from population-level color changes, such as industrial melanism observed in the Peppered Moth (Biston betularia). During the Industrial Revolution, pollution darkened tree trunks, leading to a rise in dark-colored Peppered Moths, as they were better camouflaged from predators. This shift occurred over many generations due to natural selection favoring the darker genetic variant, not an individual moth changing color within its lifetime. The dark coloration is linked to a mutation involving a transposable element in the cortex gene, which affects wing development.
External factors can alter a moth’s appearance, which may be mistaken for a true color change. Over time, moth wings experience wear and tear, leading to the loss of tiny scales that make up their color and patterns. This can dull or alter the perceived color, making a moth appear faded or lighter than its original vibrant state. Moisture can also temporarily impact a moth’s appearance; when wet, colors may appear darker or different due to changes in how light interacts with saturated scales.
Lighting conditions play a role in how we perceive a moth’s color, especially those with structural coloration. Different light sources or viewing angles can cause iridescent colors to shift, creating an illusion of active color change. For instance, structural blues might appear more vibrant or subdued depending on the angle of light incidence. While not a physiological change, natural aging can also cause some moth colors to fade slightly over their lifespan due to environmental exposure, such as sunlight.