Why Are Moths Attracted to Lightbulbs?

Confused Navigation

• The most common explanation of moths' attraction to light rests on the design of their internal navigation system. Moths adjust their flight path to maintain a constant angle relative to the sun or moon's bright light. During the day, the sun is the brightest object and moths can easily use this method to fly in a straight line. However, at night, bright artificial lights dominate the weaker glow of the moon. Moths did not evolve in an environment with lightbulbs, thus their navigational systems are not prepared to handle close, bright objects. When these insects try to maintain a constant angle relative to a lightbulb, they continuously turn and spiral into the source.

Ultraviolet Attraction

• Another theory suggests that moths are attracted to the ultraviolet light emitted by lightbulbs. Moths feed on the nectar of flowers, many of which reflect ultraviolet light from the sun or moon to attract pollinating insects. The ultraviolet patterns on flower petals alert insects to the presence of food. Because moths did not evolve around artificial sources of ultraviolet light, they may mistake the ultraviolet rays from common lightbulbs as a signal for food.

Morning Response

• According to Dr. Henry Hsiao, a professor of biomedical engineering at the University of North Carolina, there may be another explanation for the moths' confusion. Most species of moth are nocturnal, meaning they are primarily active during the night. During the day, their camouflaged wings allow them to hide and sleep safely away from predators. Hsiao postulates that moths are tricked by the bright artificial light and believe it is morning. Their instincts direct them to fly upward at the break of dawn and seek a place to hide, bringing them dangerously close to the light source.

Fatigue and Confusion

• Whatever the reason a moth flies close to a light source, it remains nearby in a state of disorientation. If the bright light confuses the moth into believing it is day, the insect may settle nearby to sleep. The moth may also alight out of fatigue after spiraling for long periods, due to navigational problems. Since moths have no evolutionary history of associating bright lights with high temperatures, they may even land unknowingly on surfaces that are too hot to survive.