Add fireflies to the list of insects in massive decline, often called the “insect apocalypse.” That was the broad upshot of a study released today in the publication BioScience.
According to the report, firefly populations face a triple threat posed by rapid development, artificial-light pollution, and pesticides.
“Lots of wildlife species are declining because their habitat is shrinking, so it wasn’t a huge surprise to see that as the biggest threat,” said Sara Lewis, a professor at Tufts University and lead author of the paper.
Based on an anecdotal survey of 49 leading firefly researchers from around the world, Lewis said the single largest threat reported is the disappearance of the meadows, forests, and wetlands fireflies need to reproduce.
“Some fireflies get hit especially hard when their habitat disappears because they need special conditions to complete their life cycle,” she said.
Lewis says the lovable lightning bugs also have significant economic value. Their bioluminescent qualities have been used by scientists to spot bacteria in packaged meat and illuminate tumors in cancer patients.
In addition to impact from development, the paper also highlighted the role that intensification of agriculture and the increased use of pesticides and fertilizer is playing on insect populations.
“The impact of pesticides on fireflies varies from region to region,” said Candace Fallon, a conservation biologist with the Xerces Society for Invertebrate Conservation.
While Fallon says more research still needs to be done to assess the precise impacts of pesticides on fireflies, the adverse effects of neonicotinoid pesticides on non-target insects such as bees and aquatic insects has been well-established.
Neonicotinoids are common insecticides often used as a seed coating for crops like corn and soybeans. The EU banned the chemicals from outdoor use in 2018.
And, unlike older generations of insecticides which have a relatively short half-life, Fallon says so-called “neonics” can persist in plants, soil, and groundwater for months and years.
“One of the things people don’t realize about fireflies,” she said, “they spend the majority of their life living underground, feeding on small invertebrates like snails, slugs, and earth worms, which are all impacted by neonics.”
Bright Lights, Big City
The BioScience paper says the second most common threat to fireflies is artificial light at night.
“There is all kinds of evidence that high levels of background light at night interferes with firefly courtship rituals,” said Tufts’ Lewis.
Lewis says the luminescent signal some fireflies use to attract mates is impacted by light pollution from homes and street lights.
“They use light the way we use texting,” said Lewis. “They use it find potential mates, and all that artificial light makes it harder for the females to see that signal from the males.”
Of the 170 species of fireflies and glowworms found in the U.S., only one is currently being reviewed for conservation status.
Last December, the U.S. Fish and Wildlife Service announced that it would review the Bethany Beach Firefly for listing under the federal Endangered Species Act. The service now faces a deadline of 12 months to determine whether it will be listed or not.