Sign up for CNN’s Wonder Theory science newsletter. Explore the universe with news about fascinating discoveries, scientific developments and more.
At night, it’s not unusual to see a large number of moths and other insects circling a porch or street lamp — but their reasons for being there are probably very different than what most people think, new research shows.
The insects aren’t actually attracted to the glow like “moths to a flame,” as the old saying suggests, but rather caught in a disorienting orbit around the artificial light, scientists reported in a study published Jan. 30 in the journal Nature Communications .
Using motion cameras – and filming with infrared lighting so as not to disrupt the creatures’ vision – the researchers showed that when the insects flew around a light source, they tilted their backs toward the light and tilted their bodies in that direction. . By maintaining this orientation, the hapless creatures created strange trajectories and steering patterns, according to the study.
Gaining a better understanding of the impact of artificial light on these winged creatures is crucial as light pollution plays an increasingly important role in the decline of global insect populations, the researchers wrote.
Artificial light confuses nocturnal insects
When artificial light doesn’t interfere, nocturnal insects keep their backs turned to the direction that is brightest, usually the sky versus the ground.
This evolutionary trick has helped the critters know which way is up and keep them level during their night flights. However, when the insects pass an artificial light source, they become disoriented, believing that the man-made lighting is the sky, said co-lead study author Samuel Fabian, an entomologist and postdoctoral researcher in the department of bioengineering at Imperial College London .
“Insects in the air don’t naturally know which way is up, so they don’t have a good way to measure that. … It is believed that the light is the direction from above, but that is wrong. And when you tilt, it creates strange steering patterns, just like if you ride a bicycle and tilt to one side, you start steering in a big circle. to get a little funky,” Fabian said.
Orbit, turn, turn around
The research team collected hundreds of slow-motion videos recording the behavior of butterflies, moths, bees, wasps, dragonflies and damselflies, and found that the creatures were not attracted to distant lights. The insects seemed to be drawn in only when they passed a light that was close by. Consistently, the vast majority of subjects turned their backs to the light, even if this prevented sustained flight.
“When people notice it, like around their porch or a streetlight, it may seem like they’re flying straight toward it, but that’s not the case,” said co-lead study author Yash Sondhi, a postdoctoral researcher at the Florida Museum of Natural. History, in a press release. Sondhi contributed to the research while he was a doctoral student in biology at Florida International University in Miami.
The team observed three common responses to the insects’ light source, including spinning the light, turning (which caused the insect to climb steeply above the light), and reversing, in which the insect turned and crashed into the ground.
Some fast-flying insects, such as dragonflies, orbited the lamp for several minutes, Fabian said.
In one experiment, the researchers simulated the night sky by shining a light on a white sheet aimed above it, and found that the insects had no trouble navigating underneath it. If the insects were inherently looking for the light, they would have bumped into the sheet, Fabian said.
“The behavior of flying insects in the presence of artificial light close to the ground is non-uniform and surprisingly complex in a way that has not previously been well documented,” said Floyd Shockley, collections manager of the entomology department at the Smithsonian National Museum of Natural History in Washington, DC.
“The insects do not fly directly toward the light, but orient themselves so that they remain perpendicular to it, creating the illusion of attraction,” Shockley, who is not involved in the study, added via email.
More theories about the strange behavior
Previous theories about why many insects fly erratically around light sources include the idea that they are attracted to heat and that the creatures – especially those that traditionally lived in caves and holes in trees – believe the light source is an escape to the outside.
The most common is that insects confuse the light with the moon, which they use as a compass signal. Because the bugs don’t fly directly toward the light and the behavior has also been observed in species that don’t migrate and don’t use compass signals, these old theories no longer seem likely, Fabian said.
“I think the biggest barrier to solving this problem for so long has been dealing with low-light conditions, small animals, and high speeds and unpredictable movements,” said entomologist Jason Dombroskie, manager of the Cornell University Insect Collection and the Insect Diagnostic Lab. not involved in the study. “The results speak for themselves. They make a pretty convincing argument that we can reject many of the other theories, at least in general.”
Light pollution and insect decline
The world has experienced widespread “loss of night” – scientists found light pollution was increasing 2.2% per year in a November 2017 report that looked at the world’s radiation through the first calibrated satellite radiometer for nighttime illumination.
The increase in artificial light has several harmful effects on wildlife, including habitat loss and fragmentation, according to a March 2022 article cited by the National Wildlife Foundation.
The authors of the new study noted that light pollution is a growing cause of insect declines, citing a September 2020 report that found artificial light affected moth behavior when it came to reproduction and larvae development.
The new findings could help conservation by spurring research into how to minimize the effects of light pollution on the insects, Dombroskie said. “I always advocate that if the light doesn’t do anything, you should turn it off.”
For more CNN news and newsletters, create an account at CNN.com