Fireflies are the stuff of magic and faerie, at least in the minds of children (and more than a few grown-ups). They rule the midsummer night, dipping and dancing across backyards, parks, and meadows, keeping their lights on well into the small hours of the morning. Many a summer childhood memory involves an empty mayonnaise jar, a few holes nail-punched in its lid, and some hand-caught bits of starlight flashing inside.
About 2,000 species of fireflies exist worldwide, and nearly 150 of them live in North America. All have eggs, pupae, and larvae that glow, which is why the larvae are commonly called “glowworms.” While adult fireflies light up to find a mate, or in some cases, a meal, glowworms emit light to warn would-be predators to stay away. Glowworms are predatory, feeding on slugs, snails, and other soft-bodied prey. Depending on the species, adults may feed on nectar, or, in a few cases, male fireflies of other species. The carnivorous females do this by mimicking the mating flashes of other fireflies, which lures amorous (and clueless) males to be devoured. One species, the Blue Ghost, lives in the Smoky Mountains and synchronizes its flash so that every firefly in the field flashes at once.
Also called “lightning bugs,” fireflies are neither flies nor bugs — they’re beetles. Their light, or bioluminescence, is incredibly efficient with nearly 100 percent of its energy released as light. By contrast, 90 percent of the energy used by an incandescent light bulb is released as heat. The active enzyme of bioluminescence, luciferase, has medical and research applications, and scientists can now produce it artificially.
Unfortunately, fireflies’ spectacular light displays have been fading away, blinking out as fewer and fewer fireflies join the show each year. The reasons include loss of habitat, widespread use of pesticides, and increased light pollution. We can save the fireflies, but we need to act now.
We destroy prime firefly habitat at an alarming rate; clearing, leveling, building on, and paving over grasslands, meadows, fields, and forests in our quest for a place of our own. While adult fireflies can move out when the bulldozers move in, glowworms, eggs, and pupae cannot. Even adults are under pressure from the excessive lights of modern life; street lights, headlights, security lights, and even porch lights and windows can drive them away.
What can we do about the increasing firefly shortage? To borrow a line from Field of Dreams, “If you build it, they will come.” Provide fireflies with a safe environment, and they’ll move in, lighting up your backyard within a year or two. They have simple needs: relatively tall grasses, moist soil, and darkness at night, all in a pesticide-free environment.
The easiest way to start is by providing some taller grasses in your backyard. You don’t need to sell your lawn mower and allow your entire yard to return to its natural state; just allow an out-of-the-way patch to get shaggy, growing longer than usual in June and July. Even the strip of untrimmed grass under a fence will do. Ideally, select a moist spot near a downspout or a birdbath for your firefly sanctuary.
Consider installing a bog garden or rain garden where you can collect rainwater to create an ideal habitat for moisture-loving plants and glowworm prey. Your rain garden needs to be the kind that holds rainwater and allows it to gradually soak into the soil instead of funneling it away to the storm sewer. The soil doesn’t need to be soaking wet, and the area can be small. Think of it as a glowworm nursery — the adults want a place with good cover and plenty of food for their young.
Your firefly sanctuary must be clean and free of pesticides. Too often, we spray firefly habitat for mosquitoes or treat it to get rid of Japanese beetle grubs, never realizing that we lose glowworms in the process. The active ingredient in chemical lawn treatments for Japanese beetles is a broad-spectrum insecticide — it also kills many other insect species, including glowworms, regardless of whether they’re harmful or beneficial. By contrast, milky spore (Paenibacillus popilliae), which is a soil-borne bacteria, affects only Japanese beetle grubs and continues colonizing lawn soils for several years after application.
In the same vein, chemical mosquito treatments often have unintended, widespread effects, killing nontarget species. Fortunately, there is also an organic, pest-specific treatment available to gardeners called Bti (Bacillus thuringiensis subs. israelensis), which is often sold as mosquito dunks and granules and which affects mosquitoes and other true fly larvae exclusively. Both milky spore and Bti are firefly-friendly.
Fireflies also need a reliable cover of darkness to feel at home in your backyard. They flash their lights to find a mate, and too much light pollution interferes with their signaling. Studies show that even passing headlights can disrupt a field of fireflies for several minutes after the vehicle has passed. Several minutes may not seem like much compared to a whole night, but how many cars will pass that field in a night? Eliminate dusk-to-dawn lights, and keep your security lights and patio lights off, or at least burning at a bare minimum. Consider installing a privacy fence or hedge to block street lights and passing headlights. Draw your shades after dark to reduce light spilling out into your yard. You can even use light to your advantage; lead adult fireflies away from areas treated with insecticides by maintaining darkness in untreated areas.
As fields, meadows, and woodlands are cleared for new developments and manicured lawns, the natural light show of midsummer continues to fade. Hopefully, our children’s children will know the joys of dancing among glowing backyard sprites, catching bits of starlight in their bare hands, and collecting cold fire in jars to light their nightstands. Fireflies need our help. Provide them with tall grasses, clean soil and water, and the cover of darkness, and they’ll return the favor with magic only they can deliver.
1. Let some of your grass grow tall and shaggy.
2. Provide a water feature or rain garden.
3. Avoid using pesticides and herbicides on your property. If you absolutely must apply something, then both milky spore and Bti are firefly-safe.
4. Turn off your porch light at night and consider installing a hedgerow or privacy fence to reflect passing headlights from cars.
Andrew Weidman lives and writes in Lebanon, Pennsylvania. He spent many evenings as a child catching fireflies, and as an adult, he marvels at the natural “Christmas lights” that illuminate the Christmas tree farm next door on warm summer nights.
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