Buzz
Around the globe, moths consistently make perilous dives into light bulbs and open flames, so frequently that their behavior has become an idiom. What is it about these light sources that compel moths to act so recklessly?
For many years, scientists pointed to the moon as the culprit. The theory suggested that moths used the moon as a navigational guide, maintaining a fixed angle to keep their flight path straight. However, human-made lights, from campfires to porch lights, disrupted this system. The moon’s vast distance meant that the angle didn’t change significantly over long distances. In contrast, closer light sources caused the angle to shift rapidly even over short distances. If a moth mistook a light bulb or candle flame for the moon, the theory went, it would adjust its course to follow the light. This repeated course correction would lead the moth into an increasingly tight spiral, ultimately causing it to crash, either burning up in flames or bumping into the light in a final, unfortunate collision.
Reconsidering the Theory...
Over time, many flaws have been found in this theory. One major issue—perhaps the most significant—is that moths might not even use the moon for navigation at all.
There’s little evidence to support this, especially when considering that over 50 percent of moths don’t migrate and wouldn’t need celestial navigation for their relatively short-distance flights.
Additionally, moths don’t always follow a spiral pattern toward light as the moon theory suggests. In fact, most of the time, they fly directly toward it. Henry Hsiao, a professor of Biomedical Engineering at the University of North Carolina, observed moths as they approached a light source and found that, in most cases, they flew straight toward the light until they were very close, then veered off and circled it at a consistent distance.
Based on his observations, Hsiao developed a new theory. Although he's uncertain about why moths fly directly toward the light, he believes the circling behavior at close distances may be caused by a visual phenomenon known as a “Mach band.” This optical illusion causes the area surrounding a bright light to appear darker than the rest of the sky. Hsiao thinks that moths may seek shelter in this darker region for protection, circling the light until their flight path either leads them away from it—or causes them to crash into it.
Love Hurts
One theory, suggested by U.S. Department of Agriculture entomologists in the 1970s, is that the infrared light emitted by candle flames contains wavelengths similar to those found in the luminescent pheromones of female moths. In essence, it’s male moths that are attracted to the flames, mistakenly thinking they’re encountering a potential mate. While this doesn’t explain their attraction to UV light—which doesn’t match the wavelengths of moth pheromones—it does offer a fascinating glimpse into the powerful pull of love.
