A: What draws some night-flying insects, notably a variety of moth species, to a flame or other bright light is one of the perennial riddles of natural science. Several theories have been advanced over the years, but none have been universally accepted or conclusively proved.
One popular idea is that moths use the moon, a natural light source, as a navigational beacon to orient themselves, maintaining a constant angle to its rays. But, this theory goes, they mistake a bright artificial source like an electric light for moonlight and alter their flight path in such a way that they spiral toward or circle the artificial source instead, often with fatal results.
Another theory is that a very bright light creates the appearance of a dark area around it and that the moths are flying into that apparent dark space, perhaps to hide there.
Others have proposed that the bright light dazzles the moths or temporarily blinds them, or that certain wavelengths mimic a food source or potential mate.
Recent research suggests the possibility that moths exposed to bright artificial light in the light-polluted urban areas of the modern world can evolve to avoid being drawn to it and thus escape being destroyed. A study published in the journal Biology Letters in 2016 compared the behavior of populations of small ermine moths of the genus Yponomeuta found in Europe that were hatched and raised in bright urban areas with those that grew up in pristine, dark areas.
The urban populations showed a great reduction in the “flight to light” response in contrast to the moths from sheltered populations, the researchers found.
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