Study Shines Light on Urgent Threats to Fireflies

Habitat loss, light pollution and pesticide were identified as three key risks that could push the insects toward extinction

Lupine flowers and fireflies at dusk in a meadow
Light pollution is threatening firefly populations. Flickr user Mike Lewinski  under the Creative Commons Attribution 2.0 Generic

Few insects tickle our fancy quite like fireflies. Unlike many other beetles, these critters are widely regarded as beautiful thanks to their bioluminescent qualities, which light up the night skies with a flickering glow. But a new survey published in BioScience has found that humans are putting fireflies at risk of extinction around the globe.

As much as we might like fireflies, the insects have been “largely neglected in global conservation efforts,” according to the authors of the report. Population data is lacking for nearly all of the 2,000 firefly species, which can be found across a variety of habitats.

Hoping to gain a better sense of how fireflies are faring, a team led by scientists at Tufts University and the International Union for the Conservation of Nature polled 350 firefly experts from around the world, asking them to rank ten different threats on a scale of zero-to-five, in terms of the risk they pose to firefly populations. Responses varied across geographic regions, but on average, the top three threats were identified as habitat loss, light pollution and pesticide.

Some of the survey results were expected. “Lots of wildlife species are declining because their habitat is shrinking," says lead study author Sara Lewis, professor of biology at Tufts. "[S]o it wasn't a huge surprise that habitat loss was considered the biggest threat.”

Previous research has in fact shown that fireflies are put at risk as their habitat shrinks. In Malaysia, for instance, breeding populations of the Pteroptyx tener firefly species declined after riverbank mangroves where they make their home were cleared for agriculture, aquaculture and urbanization. In parts of England, Lampyris noctiluca numbers are going down, possibly due to factors like road building and ditch filling. In Japan, the problem is the loss of satoyama, traditional landscapes of streams, ponds, paddies and cultivated fields were fireflies once thrived.

The researchers were more surprised to find that many experts were also concerned about the risk of light pollution, which was ranked as the second-greatest threat to fireflies, over factors like water pollution and climate change. Bioluminescence is key to the insects’ reproduction; according to Shola Lawal of the New York Times, males flash to signal their availability and females light up to show that they are also willing mates. Artificial light at night has been shown to interfere with these courtship signals by decreasing male attraction.

Pesticides, ranked as the third highest threat, target pests—but fireflies can become their unwitting victims. Larvae are particularly vulnerable because they spend up to two years below ground or under water, where insecticide concentrations tend to be high. “Although only a few studies have investigated their direct effects on fireflies ... broad-spectrum insecticides are known to adversely affect numerous nontarget insects and other taxa,” the study authors write.

Because fireflies play a key role in their ecosystems, serving as food for birds and other animals, these threats need to be taken seriously. The study authors outline a number of recommendations for reducing risks to the glowing creatures—among them identifying critically endangered species and protecting their habitats, reducing artificial light at night, and minimizing the use of insecticide for cosmetic purposes on lawns, gardens and in public parks.

“People, certainly in the US, who don’t like insects would say, ‘I love fireflies and I’ll do anything to conserve them,’” Lewis tells Oliver Milman of the Guardian. “We want a world where they are still around.”

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