Moths cannot see infrared light. Their vision is tuned to a specific portion of the electromagnetic spectrum. While humans perceive a range of colors from violet to red, moths have evolved to detect light outside this “visible” window. This means their world is illuminated by shorter wavelengths of ultraviolet light, which are entirely invisible to the human eye.
The Light Moths Can See
Instead of infrared, moths possess a sensitivity to ultraviolet (UV) light. Their compound eyes, composed of thousands of individual optical units called ommatidia, are adapted to detect these shorter wavelengths with high efficiency. This capability provides a survival advantage, as many flowers have patterns, known as nectar guides, that are only visible in the UV spectrum. These markings act as signals, guiding moths to their food source.
The ability to perceive UV light also helps in locating mates and navigating the landscape at night. The world as seen by a moth is one of glowing patterns and pathways hidden from human sight. This vision is a product of their evolution, shaped by the need to operate in low-light conditions using faint UV radiation reflected by plants and other surfaces.
Theories on Moth Light Attraction
The spectacle of a moth circling an artificial light is a direct consequence of its visual system. The leading theory for this behavior is transverse orientation. Moths and other night-flying insects are thought to navigate by maintaining a fixed angle to a distant light source, like the moon. This allows them to fly in a straight line.
An artificial light disrupts this natural navigation system. Because the source is close, the angle of light hitting the moth’s eye changes rapidly as it flies past. In an attempt to maintain a constant angle, the moth is forced into a spiraling flight path that leads it closer to the source, trapping it in a disorienting loop.
Using Infrared for Moth Observation
The fact that moths cannot detect infrared light has a practical application for scientists. Researchers can illuminate a natural setting with infrared light and use IR-sensitive cameras to film moths without altering their behavior. This technique allows for observing natural activities like feeding and mating in complete darkness from the moth’s perspective.
This method is valuable because using visible or ultraviolet light would influence the subjects’ actions, either by attracting or startling them. By using a wavelength outside their perceptual range, observers can gather more accurate data on how these insects behave when undisturbed.