Sara Lewis: Firefly populations, which illuminate and enchant on summer evenings, are flickering out
Light pollution, pesticides and commercial harvesting are mostly responsible for this, she says.
Editor’s Note: Sara Lewis is a professor of evolutionary ecology at Tufts University, and author of Silent Sparks: The Wondrous World of Fireflies (2016, Princeton University Press). The opinions expressed in this commentary are hers.
We’re well past the Fourth of July, but my dreams are still illuminated by the spectacles of two summertime icons: fireworks and fireflies. Strikingly juxtaposed, one light show explodes boisterously, so full of crackle and boom, while the other sparkles in eerie silence.
Each year our firework displays seem bigger and more spectacular. But many firefly populations seem to be flickering out.
Fireflies! For centuries, their beauty has inspired wonder and delight. Why do these creatures seem so magical? Maybe it’s the way they instantly transport us back to once-upon-a-time summer evenings spent chasing their silent sparks across the lawn. Maybe it’s the way fireflies’ resplendent displays can transform our everyday landscapes into places ethereal and otherworldly.
Whatever the explanation, in cultures around the world fireflies elicit a nearly mystical reverence.
More than 2,000 different firefly species are spread across the globe, gracing every continent except Antarctica. In the United States and in other countries firefly ecotourism is flourishing, and people are venturing out into the night to admire their dazzling displays.
It’s a heartwarming trend, since nowadays we seem to spend much too much time plugged into our digital devices and too little time engaged with the natural world. Yet even as firefles encourage more and more people to reconnect with nature’s magic, their populations are endangered by human activities such as habitat loss, light pollution and pesticides.
Fireflies thrive in fields, forest, marshes, and mangroves. But these wild places steadily succumb as waves of development replace them with shopping malls and shrimp farms, parking lots and palm oil plantations.
Light pollution, a well-known disruptor for many nocturnal animals, poses a singular threat for fireflies. Because their courtship rituals rely on detecting luminous signals, fireflies are especially sensitive to background illumination. A recently published study of the courtship habits of European glow worms revealed that the bright halos surrounding streetlamps discourage flying males from seeking out their sedentary females. So those female glow worms who display their wares near streetlamps end up entertaining fewer suitors.
Pesticides also pose perils for fireflies. During their lengthy juvenile stage, fireflies actually spend several months living underground (or, in certain cases, underwater). Broad-spectrum insecticides like malathion and diazinon can accumulate in soils and waterways, and at high levels these indiscriminately kill insects, including beneficial ones.
Juvenile fireflies are especially harmed when these insecticides are sprayed on lawns and gardens. The systemic herbicide 2,4 –D is used to kill broad-leafed weeds, yet it’s also toxic to earthworms, a dietary staple for baby fireflies. Fireflies are thus directly and indirectly harmed by overuse of pesticides.
And there’s another, more insidious threat: commercial harvesting from wild firefly populations. Most people are surprised to learn that, for decades, U.S. fireflies were harvested en masse to extract their light-producing chemicals, and that this practice is still going on. Japanese fireflies, harvested for their luminous beauty, were nearly extinguished from the country during the early 20th century. Today, Chinese fireflies are at risk from commercial harvesting.
Chinese theme parks have recently been releasing many thousand wild-caught fireflies, which make a popular but short-lived attraction, as the adult insects soon expire. And online sales of wild-caught fireflies have also skyrocketed in China. During the romantic Qixi Festival in August 2015, millions of live fireflies were harvested from wild populations and turned into love tokens.
Are we then doomed to a world devoid of fireflies? Not immediately. Although populations overall are surely waning, we still have plenty of places where these magical insects thrive.
So how can we ensure these silent sparks will stick around for future generations to enjoy?
We can become more proactive about conserving firefly populations. Decades ago, Japan established several national monuments to protect firefly habitats. In both Thailand and Malaysia, firefly sanctuaries along mangrove rivers now safeguard prime ecotourist sites. In Taiwan, two firefly species enjoy legal habitat protection.
Such conservation efforts are expanding worldwide. In 2010, international experts gathered in Malaysia to craft a document known as the Selangor Declaration on the Conservation of Fireflies. To preserve firefly populations, they said, habitat protection must be the top priority.
The United States has 120+ different firefly species, with southeastern states hosting the greatest diversity. Here, though, fireflies have yet to secure any special privileges. Some species are common and widespread, and at present they don’t seem to need protection.
But others, such as the unique Blue Ghost fireflies (Phausis reticulata) of DuPont State Forest in North Carolina, and the synchronous fireflies (Photinus carolinus) found in Great Smoky Mountains National Park, are rare. These fireflies are distinctive in both their behavior and their ecology. Their idiosyncrasies restrict them to certain habitats and also make them more vulnerable to extinction.
Why not consider setting aside a few places where fireflies thrive? Working with local, state, and national conservation organizations, we could begin by establishing firefly sanctuaries and management plans for existing ecotourist sites. We could identify and protect biodiversity hotspots known to support many different firefly species. And we surely could prohibit commercial harvesting of wild fireflies.
More than just summertime icons, fireflies offer each of us the gift of wonder and an infallible formula for falling in love again and again with nature. Who among us would remain unmoved if we lost these stunning ambassadors for Earth’s natural magic?