‘Moths to the flame’: Scientists say insects’ behavior around light has nothing to do with gravity

‘Moths to the flame’: Scientists say insects’ behavior around light has nothing to do with gravity

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At night, it’s not unusual to find a hoard of moths and other insects circling a porch light or street lamp — but the reasons they’re there are likely very different than most people assume, a new study finds.

Insects are not actually drawn to the glow like “moths to a flame,” as the old saying suggests, but are trapped in a confusing orbit around artificial light, scientists report in a study published Jan. 30 in the journal Nature Communications.

Using motion-capture cameras — and filming with infrared lighting so as not to disrupt the creatures’ vision — the researchers showed that when insects fly around a light source, they tilt their backs toward the light and keep their bodies in that direction. . By maintaining this orientation, the unfortunate creatures created strange orbits and orientation patterns, according to the study.

Gaining a better understanding of the effect of artificial light on these winged creatures is crucial because light pollution plays an increasing role in global insect population declines, the researchers wrote.

When artificial light does not interfere, nocturnal insects keep their backs turned toward the brightest direction, which is usually the sky versus the ground.

This evolutionary trick helped the creatures know which direction was up and keep them upright during their night flights. However, when insects pass by an artificial light source, they become disoriented, thinking the man-made lighting is the sky, said study co-author Samuel Fabian, an entomologist and postdoctoral researcher in the Department of Bioengineering at Imperial College London.

Sam Fabian

Using insect-scale motion capture cameras, the researchers determined that flying insects exhibited three consistent behaviors: turning, stalling, and capsizing.

“Insects in the air inherently don’t know which direction they’re going, and they don’t have a good way to measure that. … It assumes that the light is up, but that’s wrong. And if you tilt it, it creates a kind of weird orientation pattern, with the same The way that if you’re riding a bike and you tilt it to one side, you’ll be able to steer in a big circle, and everything will go smoothly. “It’s a bit unorthodox,” Fabian said.

The study team compiled hundreds of slow-motion videos capturing the behaviors of butterflies, moths, bees, wasps, dragonflies and insects, and found that the creatures were not attracted to distant lights. The insects seem to be attracted only when light passes nearby. Consistently, the vast majority of people studied turned their backs toward the light, even if it prevented them from constantly flying.

“Maybe when people notice it, like around porch lights or streetlights, they seem to fly straight into it, but that’s not the case,” said study co-author Yash Sondhi, a postdoctoral researcher at the Florida Museum of Nature. History, in a press release. Sundi contributed to the research while he was a doctoral student in biology at Florida International University in Miami.

Sam Fabian

The study team captured the behaviors of butterflies, moths, bees, wasps, dragonflies and damselflies. One exception to the light-guiding behavior observed in the laboratory was the oleander hawk moth.

Sam Fabian

It was noted that the vast majority of people included in the study tilted their backs towards the light. The Atlas butterfly is displayed.

The team observed three common responses to the insects’ light source, including turning around the light, stalling — causing the insect to climb steeply above the light — and capsizing, in which the insect flipped over and hit the ground.

Some fast-flying insects, such as dragonflies, remained in orbit for minutes at a time, rapidly circling the lighting device, Fabian said.

In one experiment, researchers simulated the night sky by shining light on a white sheet of paper facing upward, and found that insects were able to move underneath it without problems. Fabian said that if the insects were naturally searching for light, they would have collided with the cover.

“The behaviors of flying insects in the presence of near-ground artificial light are surprisingly non-uniform and complex in a way that has not been well documented before,” said Floyd Shockley, collections manager at UCLA’s Department of Entomology. Smithsonian National Museum of Natural History in Washington, DC.

Sam Fabian

Moths and other insects can get caught up in a confusing orbit around artificial light sources like street lamps and porch lights.

“The insects do not fly directly toward the light but are oriented in such a way that they are perpendicular to it, giving the illusion of attraction,” Shockley, who was not involved in the study, added via email.

Previous theories about why so many insects fly erratically around light sources have included the idea that they are attracted to heat and that the creatures—particularly those that lived in caves and holes in trees—think the light source is an escape outward.

The most common reason is that insects confuse the light with the moon, which they use as a compass reference. Since the creatures do not fly directly toward the light, and this behavior has also been observed in non-migratory species that do not use compass signals, these old theories are no longer likely, Fabian said.

“I think the biggest obstacle to solving this problem for a long time is dealing with low-light conditions, small animals, high speeds, and unpredictable movement,” said entomologist Jason Dombroski, director of Cornell University’s Insect Collection and Insect Diagnostics Laboratory. Do not participate in the study. “The results speak for themselves. They make a very compelling case that, you know, we can ignore a lot of other theories, at least in general.”

Light pollution and reduced insect populations

The world has seen a “loss of nighttime” on a massive scale – with scientists finding that light pollution has risen at a rate of 2.2% per year in a November 2017 report, which looked at the world’s radiation with the first satellite radiometer calibrated for nighttime lights.

The increase in artificial lights has several harmful effects on wildlife, including habitat loss and fragmentation, according to a March 2022 research paper cited by the National Wildlife Foundation.

The authors of the new study noted that light pollution is a growing cause of insect declines, pointing to a September 2020 report that found that artificial light affects moth behaviors when it comes to reproduction and larval development.

Dombroski said the new findings could help insect conservation by boosting research on how to reduce the effects of light pollution on insects. “I always advocate that if a light isn’t doing anything, turn it off.”

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