Fireflies at risk of extinction due to the climate crisis, light pollution, and more

The world is getting darker — and I don't just mean due to the looming threat of the climate crisis. According to new research, fireflies — of which there are more than 2,000 species on Earth — are at risk of extinction.

Of the 2,000 or so species of fireflies, between 125 and 200 can be found in the U.S. Even though there has been evidence that firefly populations have been dwindling for a while, fireflies are still not protected by the country's Endangered Species Act. 

The new research, conducted by professors at Tufts University, was published Monday, Feb. 3 in the journal Bioscience. As the authors explain in the study's abstract, even though there has been some evidence of declines in firefly populations, there has not yet been an exhaustive study looking at the conservation status and threats facing all 2,000 firefly species worldwide. So, they set out to change that, in hopes that new data could lead to greater protection for fireflies.

For the study, the authors surveyed experts from different geographic regions across the globe to figure out the most significant threats to fireflies, which risk factors may increase vulnerability of specific firefly species, and why it's essential to establish firefly monitoring schemes and conservation programs.

Across the eight regions studied, the three most significant threats to fireflies observed are habitat loss, artificial light, and pesticide use. Other risks include water pollution, drought, rising temperatures, rising sea levels, storms, flooding, invasive species, tourism, overharvest, and the climate crisis in general.

Almost all of those factors are related to the climate crisis and the ways we are using the Earth's resources to sustain our growing population. Habitat loss, the top risk factor, is typically a result of human activities, from developing new buildings or houses to destroying land for factory farming or agriculture to logging to pollution. 

Artificial light at night (ALAN) is the second most serious risk factor. In fact, more than 23 percent of the Earth's land surface is illuminated by ALAN, and that light pollution interferes with fireflies' bioluminescence (more on that below). 

And pesticide use, the third most significant risk factor, obviously directly impacts fireflies. According to the study, broad-spectrum insecticides are specifically known to negatively impact non-target insects. And pesticides do not only impact fireflies if they are directly in the line of spraying — pesticides can also persist in the soil, bodies of water, and in the bodies of fireflies' prey.

Fireflies don't just light up to entertain humans on summer nights — they actually use their bioluminescence powers to find mates. As explained by the Center for Biological Diversity, male fireflies flash their lights to attract female fireflies; if a female is interested, she will flash her lights back, and they will mate. 

Additionally, if a female eats a male of another firefly species, she will gain their protective toxins. So, after mating, females will sometimes continue flashing their lights but imitate the patterns of other firefly species (since each species has a different pattern), hoping to attract a male of that species, and then she will eat him, according to the CBD. (It sounds like a video game, but it's true.) If there is a lot of ALAN near firefly habitats, those artificial lights could interfere with the fireflies' natural light patterns.

To help protect firefly populations, the authors think humans need to: identify the most critically endangered firefly species; establish sanctuaries to protect them; work to control and reduce light pollution (ALAN) near firefly habitats; reduce insecticide use, especially when used for aesthetic purposes (such as on home lawns and in public parks); and develop sustainable tourism guidelines for firefly tourism.