It’s commonly known that moths are attracted to bright light bulbs and often circle them, giving rise to the saying “like moths to a flame ”. There are a number of theories as to why moths engage in this often life-threatening practice .

The traditional hypothesis is that moths mistake the light source for the moon . Moths are thought to migrate long dis-tances, and it is believed that they use the moon to navigate on their journeys, it being a relatively stationary reference point from which to gauge direction . They can travel in straight lines by maintaining a constant angle to the moon . When the moth mistakes an artificial light source for the moon, it continues to keep a constant angle to the light .


However, because of its close proximity to the light, this re-sults in it spiraling toward it in a confused state .

While it’s accepted that moths do indeed use the moon to navigate, the problem with the idea that moths mistake lights for the moon is that they tend to fly directly to a light and then spiral around it, rather than spiraling toward it as soon as they spot it .

A second theory is that moths fly toward lights in an attempt to keep warm . However, this is discredited because it turns out that moths are more attracted to ultraviolet light bulbs than those emitting normal visible light, which are warmer . In fact, moths are more sensitive to certain wave-lengths of light—for example, they are more attracted to the colors in white light than to yellow .

A third theory—and the most compelling—is that moths are initially attracted to a light source and will fly directly toward it, but then, once there, will try to avoid the light and seek darkness (perhaps because they’re nocturnal crea-tures) . As a result of a peculiarity in the moths’ vision, they perceive that the darkest place in the sky is an area about one foot from the light source . As a safety mechanism, the moth seeks out this darkest place and remains there, causing it to circle the light frantically within the dark band .

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