A Future for Fireflies?

By Elizabeth Collaton, Extension Master Gardener

This is the summer of our climate emergency on full display. Much of the country swelters under relentless triple-digit temperatures, and the ocean off the southern Florida coast has recently reached 101.1 degrees, according to The Washington Post, resulting in the bleaching and death of coral reefs vital to our fisheries. Flash flooding has submerged communities and blown out vital infrastructure, not to mention the lives lost to fast-rising flood waters. The brief timeframe for decisive action on climate change seems suddenly to have collapsed upon us. We hope for a reprieve. We see little relief in sight, especially when observed on a global scale. Yet, and maybe because of this, a hyperlocal focus on the sustainability potential of my modest suburban yard has kept me going. Is this optimism or head-in-the-sand behavior? Maybe both, but taking concrete steps to make even a small patch of land a refuge for biodiversity can feel like a tonic against mounting climate despair.

Let’s back up a little, though. Last spring our household completed the third year of leaving the leaves throughout the yard. I had some questions about the impacts of this leaf-litter layer on the insects and soil biome underneath. Was it necessary to leave all the leaves, including those leathery oak and magnolia leaves? Was it safer for the insects if I waited to remove the leaves until May, when temperatures tipped into the 50’s? Though committed to flipping the aesthetic on standard lawn care practice, I wanted some evidence that my actions were producing results, even as many of our neighbors’ yards looked tidy and freshly mulched. 

A conversation with Richard Joyce, an endangered species conservation biologist and co-coordinator of the Firefly Atlas at the Xerces Society for Invertebrate Conservation, was useful in providing more context for understanding the human contributions to what some scientists are calling a global insect apocalypse. Joyce has been researching fireflies throughout the U.S. to understand their diversity and decline and to document, with the help of amateur scientists and casual observers, where fireflies are making a comeback. He acknowledges that firefly research is decades behind what scientists know about birds and plants, and even monarchs, bumble bees, or honey bees, which he labels “semi-domesticated agricultural animals.” By using citizen science portals like the Firefly Atlas and field research, Joyce and others hope to establish baseline data to inform best practices and policy ideas for minimizing human impacts on fireflies.

So what does a conservation biologist wish more people knew about fireflies? Aside from the big dipper or common eastern firefly (Photinus pyralis) so familiar in the Mid-Atlantic Region, there are 170 named species in the U.S., 28 of which can be found in Virginia. Astonishingly, the adult firefly’s twinkling arrival in early summer is the culmination of a 1-3 year larval stage, during which tiny but voracious larvae feed on snails, earthworms, and other soft-bodied animals underground. During this stage, they must amass all the energy and fat they will need to court, mate, and lay eggs, since many adult fireflies have very small mouthparts and do not feed. The adult Phontinus pyralis lives only about 30 days, and then the cycle begins all over again, with eggs hatching about 4 weeks later. While Joyce was eager to talk fireflies, he made it clear that the challenges facing their survival go well beyond leaf litter.

Leaving the Leaves

The Xerces Society’s Leave the Leaves program is the organization’s signature public education campaign. There is no doubt that leaving the leaves is beneficial to existing firefly populations. Adding organic matter leads to healthier soils which, in turn, support an abundance of earthworms, snails, and other soft-bodied animals on which the firefly larvae feed. But given the long larval stage for such a tiny beetle, leaving the leaf litter to accumulate season after season is desirable over letting leaves overwinter in place, only to be removed in the spring. Joyce acknowledged the barriers some homeowners face in their efforts to provide this type of habitat on a continuous basis due to homeowner association restrictions or simply the aesthetic shift in mindset required in seeing leaf litter as a natural part of the landscape rather than something to be hauled away during spring and fall cleanup. Still, he emphasizes the value of, at a minimum, designating a high-moisture part of the yard where the grass is left to grow high, the leaves are allowed to settle permanently, and perhaps a fallen log is left to rot in place.

Habitat Protection

Habitat loss on a grand scale is driving the insect apocalypse, fireflies included. In her book, Silent Sparks, Tufts University biology professor Sara Lewis describes the struggle for balance in Thailand and Malaysia, where even though firefly ecotourism has boomed, firefly populations remain vulnerable as mangroves give way to oil palm plantations and shrimp farms. One problem with habitat destruction—even suburban land redevelopment—is that fireflies tend not to move around that much. A bumble bee’s range is perhaps half a mile. Fireflies have a smaller habitat, tending to hang around within a few meters of where they were born. Once habitat is wrecked, paved over, or collected by a backhoe to make room for a home addition, that particular population and any future eggs are often lost. Proximity to a park, a river, or a wetland, Joyce notes, can increase the likelihood that a firefly population will rebound.

Light Pollution

Like many insects, fireflies are guided by a natural circadian rhythm. Light pollution in the form of yard and house lights, street lamps, the increasingly common practice of ‘uplighting’ to showcase horticultural or architectural highlights, poses grave dangers to fireflies. Nighttime light can confuse them by obscuring the fireflies’ own flashing and can also draw males away from habitat where the females are, thus reducing their mating success. Joyce notes that these factors are less harmful for the big dipper, which begins to flash around sunset. For other species that wait until full darkness, artificial light is more detrimental. Trends to minimize artificial light, such as downlighting, light shielding, setting timers, and using lower-wattage lights can help. 

Pesticides

Finally, since healthy firefly populations depend on healthy soils to support their lengthy larval stage, minimizing the use of pesticides, fungicides, and herbicides can help protect the vast web of bacteria, fungi, invertebrates, mammals, and birds that interact with the soil. Recalling that the average American lawn absorbs three times the pesticide concentrations seen in agricultural settings, it is fair to worry about how popular broad-spectrum products applied according to the manufacturer’s label will impact fireflies and the organisms they feed on.

All of these steps are within our reach and achievable as we gardeners work to expand the biodiversity of our modest yards and gardens. Against the dire backdrop of the climate change impacts we are seeing this summer, it seems the least we can do.