In the world of insects, fireflies evoke warm memories of summer nights spent watching their lights glow in our patios and parks. There are more than 2,000 different species in the world - technically, fireflies are beetles and they don't all light up, but new research suggests they face threats wherever they are found, and that's largely due to human behaviors.
Firefly specialists from nearly every continent participated in a study conducted by Dr. Sara Lewis of Tufts University, which has campuses in the United States and France. She asked them to assess the threats they see to fireflies in their own nations and describe the impacts of the main threats on firefly populations.
Lewis and his team then grouped the responses into geographic regions to rank threats, with habitat loss being the number 1 concern. It was closely followed by light pollution and then pesticide use.
"A lot of wildlife species are declining because their habitat is shrinking," Lewis said, "so it wasn't a big surprise that habitat loss was seen as the biggest threat." The impacts of habitat loss are most pronounced when a species needs specific conditions, as is the case with Pteroptyx, a Malaysian firefly with a complex intermittent ritual that lives among the mangroves.
“Across Southeast Asia, large areas of riparian mangroves have been cut down for oil palm plantations, shrimp farms, or flood mitigation, rendering these sections unsuitable for the growth and development of Pteroptyx firefly larvae and their snail prey ”, explains the article published in the journal BioScience.
"Additionally, Pteroptyx adults gather for nocturnal courtship displays in specific, prominent trees located along mangrove rivers, and many of these display trees have been removed," add the authors. Similar challenges face fireflies in the Amazon in Brazil, in the logging regions of Mexico, and in coastal wetlands in the United States, where the human footprint is displacing them. Some species do not fly at all, and when their habitats begin to shrink, they cannot simply migrate elsewhere.
While more than half of all respondents said habitat loss was a top threat, a third of them mentioned light pollution. This is especially problematic for firefly species that depend on their luminescent "mating dances" for reproduction, signaling potential mates at night. Streetlights, billboards, sports stadiums, and factories emit artificial light at night that can interfere with insects.
"By conservative estimates, more than 23 percent of the world's land surface now experiences some degree of artificial brightness from the night sky," Lewis and his team note. "Light pollution was perceived as the main threat to fireflies in East Asia and South America, and the second or third most serious threat in most other regions."
Avalon Owens, a Tufts doctoral candidate in biology and a co-author of the study, says that switching to LED bulbs may use less energy, but it doesn't help reduce the impacts of artificial light. "Brighter is not necessarily better," Owens said.
And just as with extinction threats to other insects, pesticide use also poses risks to fireflies. That's especially true in Europe, where loss of habitat for agricultural activities followed by pesticides comes as a double whammy.
Tourism is also a problem, especially in Asian countries like Thailand and Japan. Whether from speedboats crossing rivers or flashing cameras that interrupt the night, the authors warn that “if such tourism is not managed responsibly, it can threaten local firefly populations by disturbing larval and adult habitats and interfering with adult reproduction. ”.
The authors' recommendations for moving forward focus on these four themes: Protect habitats, they say, while reducing light pollution and pesticide use, and develop sustainable tourism plans for the future.