The sight of moths fluttering around a porch light is a common occurrence, leading to the widespread belief that all moths are drawn to light. This image, often romanticized as “like a moth to a flame,” simplifies insect behavior. However, this common perception captures only a small part of a more intricate reality. While many moths respond to artificial illumination, whether this applies to every species is a nuanced question.
The Complex Reality of Moth Attraction
Not all moths are attracted to light; the phenomenon is more complex than commonly understood, as while many nocturnal species exhibit positive phototaxis, not every species responds this way. Some moths are indifferent to light sources, showing no attraction or repulsion. Other species, such as the Old Lady moth (Mormo maura), are repelled by light, demonstrating negative phototaxis. Diurnal moths, active during the daytime, are not attracted to artificial night lights, as their life cycles are adapted to daylight conditions. This variation underscores that light attraction is not a universal trait, highlighting diverse moth interactions with illuminated environments.
Understanding Why Moths Respond to Light
Reasons certain moths are drawn to light involve complex navigational instincts. The most accepted theory is “transverse orientation,” also known as “lunar navigation.” Moths use distant natural light sources, like the moon or stars, for orientation, maintaining a constant angle to fly in a straight line. Artificial lights, being closer and emitting light in all directions, disrupt this natural navigation system. When a moth attempts to keep a constant angle to a nearby artificial light, it results in a disorienting spiral path drawing it closer.
This disorientation explains the erratic flight patterns observed around lamps, where moths may circle endlessly or even fly upside down. Moths are sensitive to ultraviolet (UV) light, prevalent in many artificial sources, which increases their attraction. UV light, with its shorter wavelengths, is attractive to moths, mimicking natural cues for foraging and navigation. While other theories, such as an escape mechanism or confusion with mating signals, have been proposed, disorientation due to navigational interference remains the dominant explanation.
Beyond Attraction: How Light Affects Moths
Artificial light impacts moths beyond simple attraction, posing negative consequences for their survival and the broader ecosystem. Light pollution disrupts crucial nocturnal behaviors, including feeding, mating, and migration. Moths drawn to lights spend energy circling, becoming exhausted and vulnerable, and are deterred from natural activities like feeding and egg-laying. This altered behavior reduces foraging, impacting their ability to find food and reproduce.
Artificial lights also increase moths’ vulnerability to predators, such as bats and birds, which learn to congregate around illuminated areas where moths become easy targets. Studies show increased predation rates on caterpillars near light sources, risking both adult moths and their larval stages. Light pollution contributes to declining moth populations, with potential cascading effects on plant pollination, as moths are important nocturnal pollinators. Even dim artificial light, like skyglow, can interfere with moth development and behavior, showing the pervasive and detrimental effects of light on these insects.