Study finds habitat loss, lighting threaten the firefly’s charm

17 Februari 2020

In the insect world, the firefly conjures up warm memories of summer nights spent watching their lights shimmer across our yards 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, and that’s largely because of 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 top threats on firefly populations.

Lewis and her team then grouped the responses into geographical regions to rank the threats, with loss of habitat as the No. 1 concern. It was closely followed by light pollution and then pesticide use.

“Lots of wildlife species are declining because their habitat is shrinking,” said Lewis, “so it wasn’t a huge surprise that habitat loss was considered the biggest threat.” The impacts of habitat loss are more pronounced when a species needs specific conditions, as is the case with Pteroptyx tener, a Malaysian firefly with a complex flashing ritual that lives among mangroves.

“Throughout Southeast Asia, large areas of riverbank mangroves have been cleared for oil palm plantations, shrimp farms, or flood mitigation, making these sections unsuitable for the growth and development of Pteroptyx firefly larvae and their snail prey,” explains the paper, published this month in the journal BioScience.

“In addition, Pteroptyx adults gather for nightly courtship displays in specific, prominent trees located along mangrove rivers, and many of these display trees have been removed,” the authors add. Similar challenges face fireflies in the Amazon in Brazil, in logging regions of Mexico, and in wetlands of the coastal United States where the human footprint is crowding them out. Some species don’t fly at all, and when their habitats start shrinking they can’t just migrate to another spot.

While more than half of all respondents said habitat loss was a top threat, a third of them named light pollution. That’s especially problematic for firefly species that rely on their luminescent “mating dances” for reproduction, signaling in the night to potential partners. Streetlights, billboards, sports arenas and factories all emit aritifical light at night (ALAN) that may interfere with the insects.

“By conservative estimates, more than 23 percent of the global land surface now experiences some degree of artificial night sky brightness,” note Lewis and her team. “Light pollution was perceived as the top 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 study co-author, says switching to LED bulbs may use less energy but doesn’t help reduce the artificial light impacts. “Brighter isn’t necessarily better,” Owens said.

And as with extinction threats to other insects, pesticide use also presents risks to the fireflies. That’s especially true in Europe, where habitat loss to agricultural pursuits followed by pesticides delivers a double blow.

Tourism is a problem too, especially in Asian nations including Thailand and Japan. Whether from speedboats cruising rivers or camera flashes interrupting the night, the authors warn that “if such tourism is not responsibly managed, 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 issues: Protect habitats, they say, while reducing light pollution and pesticide use, and develop sustainable tourism plans for the future.

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