With the world on the brink of an "insect apocalypse," scientists have revealed yet another way we may be wreaking havoc on our six-legged friends: light pollution.
Two new studies underline the unintended effects on insects of artificial light at night, and add to broader concerns that our understanding of humanity’s impact on nature is still a work in progress.
One of the studies describes how a “biblical plague” of grasshoppers in 2019 was drawn to the bright city lights of Las Vegas. The other suggests that human-made lighting at night could affect the love lives of fireflies – and perhaps even hinder their ability to mate and survive as a species.
“Even after all these years, the first time I see fireflies each year I’m always so taken with it,” says Avalon Owens, an entomologist at Tufts University. “Their display looks so magical.”
Owens has studied the flashing of fireflies for almost a decade, from summer-night displays in North America to the subtropical island of Taiwan, where fireflies can be seen throughout the year and are associated with the spirits of ancestors.
There are many species, but true fireflies all belong to the Lampyridae family of beetles, which chemically produce tiny flashes of light in organs on their abdomens. Their flashing patterns depend on the species, but all fireflies primarily use their flashes to find mates that otherwise can’t be seen at night, Owens said.
Previous research suggested the mating signals of male fireflies are inhibited by white light. But the study by Owens and her colleagues published last month in the journal Insect Conservation and Diversity looks at both male and female fireflies and their sensitivity to different colors of light.
The results are not good: The researchers exposed “courting” pairs of the common North American firefly Photinus obscurellus to five different colors of light. They found that all colors of artificial light “significantly suppressed” the courtship flashes of the firefly pairs, and that bright amber light was the worst.
That finding will dismay environmentalists who’ve proposed amber lighting for streets and parks at night, because it’s thought to have less impact on wildlife than regular lights. But that doesn’t seem to be the case.
“There is no color of light that’s perfect,” Owens said. Instead, “we should focus on minimizing the time that lights are on and how bright they are.”
She suggests outside lights should be fitted with motion sensors that can’t be triggered by fireflies, or with timers to shut them off when no humans are around. People who venture out to look for fireflies could use a dim red flashlight – the color found to have the least impact – and turn it off when they find them, she said.
“We don’t need to have this constant lighting," Owens said. "It’s just very harmful.”
The other study, published Tuesday in the journal Biology Letters, looks at an outbreak of grasshoppers in Las Vegas in 2019. The insect swarm could be seen on the Doppler radar signals used to monitor rainfall, which showed that more than 45 million grasshoppers took flight at the peak of the outbreak, and that they concentrated at night over areas of high-intensity lighting in the city.
Elske Tielens, the lead author of the study and an insect ecologist at the University of Oklahoma, said it was one of the first times that the large-scale effects of artificial lights on insects had been documented.
“This knowledge can help researchers both conserve our diverse world of insects, as well as manage important pest species," Tielens said.
And energy-efficient LED lights could be making things worse: “Unfortunately the short wavelength of LED lights is actually more attractive to insects,” Tielens said in an email. “That doesn’t mean we should or shouldn’t use LEDs, but it is important to know the trade-offs and effects on our natural world.”
The new insect studies and others highlight some of the harmful side-effects on wildlife of human-made light pollution, said John Barentine, a spokesman for the International Dark-Sky Association, based in Tucson, Arizona.
“There is now much more than just whether or not we can see the stars."
John Barentine, a spokesman for the International Dark-Sky Association,
“Wherever researchers have looked at the effects of light at night on individual species, in almost every situation it is usually negative," he said.
Scientists can't yet quantify exactly how light pollution affects wildlife species, but it could either draw them or drive them away from their usual activities, such as finding food or mates, he said.
The association, which will convene an International Dark Sky Week in early April, began more than 30 years ago out of concerns about the growing difficulties of viewing stars at night. But it now also advocates for limitations in night lighting because of its impacts on wildlife and its potential to affect energy security, climate change and public safety.
“There is now much more than just whether or not we can see the stars," he said. "We are finding that it has all of these other impacts in other areas."