Why do artificial lights hold such a fatal attraction for moths?
Around man-made lights, such as the light on a verandah, the angle to the light source changes as a moth flies by, which disorientates it.
There have been several theories and hypotheses, but scientists aren’t sure. It seems it will have to remain a mystery for now… but moths are evolving.
When it comes to people, it’s usually not difficult to determine what the underlying motivation for such behaviour is, but when it comes to moths there are a few theories about why the insects head straight for the flame of a candle or for artificial lights. But, it seems that’s just what they are – theories.
Artificial lights disorientate moths
Some entomologists believe moths fly to unnatural light sources because the lights interfere with their internal navigation systems. Moths evolved when the light on Earth came mostly from the sun, the moon and the stars. The theory is that in a behaviour called transverse orientation, some insects navigate by flying at a constant angle relative to a distant light source, such as the moon.
Around man-made lights, such as the light on a verandah, the angle to the light source changes as a moth flies by, which disorientates it.
The problem with this theory is that light bulbs may be new on evolutionary time scales, but fire has always been around. Wouldn’t moths be extinct if they keep on flying into flames?
Watch: Why moths are obsessed with lamps
Male moths think candles are female moths sending out sex signals
Philip Callahan, an entomologist, working with the U.S. Department of Agriculture in the 1970s had a completely different theory.
It would follow that male moths may be attracted to candles under the delusion that they are females sending out sex signals. “The male moth is highly attracted to and dies attempting to mate with the candle flame,” Callahan wrote in a 1977 paper in Applied Optics.
Professor Jerry Powell, an entomologist at the University of California, Berkeley, who specializes in moths, told LiveScience that ultraviolet light is far more attractive to insects than infrared light. He says ultraviolet light does not contain the same wavelengths as the glowing pheromones of the female moth. Callahan had previously discovered that the pheromones are luminescent in that they glow very faintly in the dark.
Entomologists have found that moths are less attracted to artificial lights during the week of of full moon. That is because darkness triggers more moth activity.
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But moths are evolving
EarthSky reported that in 2016, two biologists published a study in the peer-reviewed journal Biology Letters on the possible evolutionary consequences of our modern, artificially-lit world on moths. They tested the flight-to-light behavior of 1 048 adult ermine moths, whose larvae they’d collected in 2007, just after the insects had completed their first molt. Some were rural moths that lived under largely dark skies and rest were urban moths from light-polluted areas. All the moths were then raised in a lab with 16 hours of daylight and 8 hours of darkness daily while they completed their life stages.
According to a report in Science, two to three days after emerging as moths, they were released in a flight cage with a fluorescent tube at one side. Moths from high light pollution areas were significantly less attracted to the light than those from the darker zones, indicating that moths are evolving to stay away from artificial lights.
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