From the Bhagavad Gita toward Merchant of Venicestorytellers have warned of the unappealing fate that awaits those drawn like a moth to a flame.
Despite the rich history of this puzzling behavior, the science of why insects gather around lights at night has never been nailed down. Popular theories propose that moths navigate by following the moon and mistake lamps for moonlight, or that insects fly toward the light to escape imminent danger.
Now researchers think they have a more convincing answer: Instead of being attracted to the light at night, moths and other flying insects get caught in its glow. It is the unfortunate consequence of an ingenious trick developed over millions of years that failed in the modern world.
According to Dr. Sam Fabian, an entomologist at Imperial College London, moths and many other night-flying insects evolved to angle their backs toward where it is brightest. For hundreds of millions of years, this was the sky and not the ground. The trick told the insects which way up they were and ensured they flew level.
But then came artificial lighting. Having to deal with new lighting sources, the moths found themselves leaning their backs toward the streetlights. This sent them into endless circles around the lamps, the insects trapped by their evolutionary instincts.
Fabián and his colleagues captured the insects’ flight paths around the lights using high-resolution infrared motion capture in the lab and high-speed infrared video recordings in Costa Rica. The images reveal that time and time again, moths and dragonflies turned their backs on artificial lights, wreaking havoc on their flight paths.
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“If the light is above them, they might start orbiting it, but if it’s behind them, they start leaning back and that can cause them to climb higher and higher until they stop,” Fabián said. “The most dramatic thing is when they fly directly over a light. They turn around and that can cause accidents. “It really suggests that the moth doesn’t know which way is up.”
The work, published in Nature Communications, suggests that artificial lighting may not bring flying insects out of the darkness, but simply catch those that fly by. “It’s almost like having a network,” Fabián said.
Researchers have long warned that light pollution is a major driving force in Dramatic decline in insect populations.. Moths and other insects that get trapped around lamps become easy prey for bats, but the lighting can also trick them into thinking it’s daytime, causing them to go to bed and skip a night of feeding.
“The effect on their flight is actually only a small component of how artificial light can ruin the lives of these nocturnal insects,” Fabián said.
He believes there are useful lessons from the research. “What I think this tells us is that the direction of artificial light is important. “If you’re going to have lights at night, you really want them to be covered and not throw a lot of light sideways, and especially not up, into the atmosphere,” he said.
Professor Gareth Jones of the University of Bristol called the work “fascinating”. “It is notable how an innate and adaptive behavior, through which an insect positions itself so that its back faces the light and therefore maintains a constant flight path, becomes maladaptive near strong point sources such as lamps” , said. “The findings suggest that a large number of insects that congregate on streetlights become trapped there as they orbit the lamps.
“Minimizing attraction and confinement in lamps will be very important to reduce the impact on insects. This could be achieved by using lights that minimize the use of short wavelengths, such as blue and especially UV rays, and potentially even producing metameric light that appears white to humans but comprises spectrums that are less attractive to insects. ”.