As dusk deepened the shadows on the edge of the forest, a small lighthouse illuminated the gloom.Soon, the twilight was full of streamers, and every blink of an eye sent a peculiar signal: “A man asks a woman for a brief union.. ” This courtship, which plays out on summer nights around the world, is a beetle of the firefly family, commonly known as fireflies.
However, the darkness in which the fireflies have been finding connection has been shattered by the glare of artificial light. Humanity’s love of lighting causes many habitable surfaces on Earth to suffer from light pollution at night. In recent years, scientists studying fireflies have heard concerns that fireflies may be declining, said Tufts University entomologist Avalon Owens.
“There’s this sense of doom. They don’t seem to be where they used to be,” she said.
Dr Owens said so little was known about how fireflies survived that it was difficult to assess whether they were at risk – and if so, why. But in a study published Wednesday in the journal Royal Society Open Science, she and Tufts University biology professor Sara Lewis revealed how fireflies respond to artificial lighting. Experiments in forests and fields, as well as in the lab, have shown that while some North American fireflies mate recklessly in light conditions, others do not complete a successful mating in bright light.
Fireflies seem to rely primarily on flashes to find each other, which means light pollution could threaten their ability to see a mate. In the four common species examined in the study, females hid on the ground and watched as males roamed the sky. When the female responds to the male’s flash with her own flash, the two enter into a conversation that can end with a session and eventual mating. In previous work, Dr. Owens and Dr. Lewis found that exposing female fireflies of the species Photinus obscurellus to light reduced the likelihood that they would respond to male fireflies.
In a forest west of Boston, scientists took on the role of female fireflies and responded to male Photinus greeni with green LED lights. The lights are either in the dark or illuminated, like street lights. Scientists have found that more than 96 percent of men prefer darkness. Then, in laboratory experiments with P. obscurellus, they observed that while dim light had little effect on successful mating, in bright light, no pair of fireflies mate. The insects spotted each other, and some even crawled past each other, but something stopped them from moving on.
“It was really important because we were all wasting time running around and counting flashes, and it didn’t matter if they were actually next to each other and didn’t mate,” recalls Dr. Owens. “It’s very worrying.”
She speculates that fireflies interpret light as day and wait in darker conditions to mate — essentially waiting for a night that never comes.
In a field in Tionesta, Pennsylvania, Dr. Owens saw something that complicates the doom and gloom of lab experiments. Bruce Parkhurst, a firefly enthusiast who lives in the area, reminded her to introduce bright outdoor lighting at the visitor center, so Dr. Owens and her colleagues studied the behavior of local fireflies in the adjacent area.
On many July nights, they captured and tagged females of two species – P. pyralis and P. marginellus — and place them in the spectral region from bright to complete darkness. Females in bright areas tended to have later and further shadows, suggesting the insects would simply move into the dark if they found the light uncomfortable. But even in places where the light nearly dazzled the researchers, the two fireflies somehow found each other and successfully mated.
“They just mate left, right and center,” Dr. Owens said. “They don’t care at all. It’s crazy to be out there and see it for yourself.”
The researchers speculate that in a group as large and diverse as fireflies—there are more than 2,000 species worldwide—adapting to different levels of darkness could mean different responses to light pollution.Of the four species in the study, P. obscurellus, an insect that has never copulated in bright light It is also least active at dusk, preferring late nights. Well, what doesn’t bother one group at all can destroy another.
Is there a version of artificial lighting that is friendly to all fireflies — a wavelength of light that works for humans and photosensitive insects? Dr. Owens has been pursuing the idea, but a generally harmless option remains elusive.
The best solution may be the simpler, more radical approach: be more aware of your outdoor lights and use them more sparingly. While this research suggests that fireflies may be able to escape light pollution and head to dark havens, if there is no dark place left for them, the symphony of twilight at night may be a thing of the past.