Can we document these luminescent beetles before it’s lights-out for them?
If you grew up around lightning bugs, it may seem that there are fewer of them sparking up the summer nights than there were a couple of decades ago. That’s because in the US alone, at least 18 species of firefly — there are an estimated 173 species in the US and Canada — now face extinction. In addition, up to one-third of assessed species may be imperiled.
The usual culprits contribute to the growing threat: habitat destruction and degradation; global warming that parches the damp leaf-litter where firefly larvae, juveniles, and females reside; and the use of insecticides and other biocontrols for crop protection, including the introduction of beetle-munching nematodes. But there’s a surprising wildcard in the deck: light pollution. Although we know them as luciferous (light-bearing), fireflies require absolute darkness to thrive. And as darkness becomes scarce, so do fireflies.
Candace Fallon is Senior Conservation Biologist, Endangered Species Program, for The Xerces Society for Invertebrate Conservation, and her Firefly Atlas project launched in March 2023 is a step toward safeguarding the future of the beloved bioluminescent beetle. Fallon explains, “Some firefly species require absolute darkness to communicate. In many species, the presence of artificial light may scramble the crucial signaling patterns between males and females. The males flash less, the females glow [or respond] less; there is less dialogue, and there’s less mating as a result.”
Also a Red List evaluator for the International Union for Conservation of Nature, Fallon says that “I was honestly shocked when I started studying fireflies about five years ago. Although people love fireflies, they are not well-studied. There’s so much we don’t know, and data deficiency means that we may lose species before we can even document them.”
The purpose of The Firefly Atlas is to gather data anywhere in the US and Canada, and, says Fallon, “…any data is excellent. The Atlas accepts negative data, as in, ‘we’re not seeing fireflies where we used to see them.’” The project is led by the Xerces Society in collaboration with the New Mexico BioPark Society and the IUCN Firefly Specialist Group. In order to make firefly identification more accessible to firefly enthusiasts, the Firefly Atlas also provides a filterable checklist for the firefly species of the U.S. and Canada, tips on how to photograph fireflies for identification purposes, and diagrams and explanations of firefly anatomy and flash patterns.
Richard Joyce, endangered species conservation biologist and co-coordinator of The Firefly Atlas, had just returned to Amherst, MA, fresh from observing fireflies in Indiana, when we spoke via Zoom. “Firefly survey work is basically one big juggling act,” Joyce said. The approach taken by entomologists of decades past, namely collecting and labeling, doesn’t cut it with fireflies, “…because many species look so similar. Morphology is only part of the delineation,” says Joyce. Observing the complex flash-patterns of courting couples potentially yields far more precise data than a mere examination of their appearance can provide. “The flashes contain information that we may not know how to fully interpret yet. It’s kind of like birdsong in terms of tempo and rhythm. Each male firefly is given a specific pattern to attract a mate. One species may produce comet-like, crescendo flashes, while another signals with a staccato flicker, even though the two species look almost identical.”
Armed with gauze net, thermometer, stopwatch and cell phone for macro-photos and voice recordings, “I try to arrive at sunset,” Joyce says. He notes that subtle variations in temperature and the effects of ambient light (including moonlight and clouds, which both block and reflect light) affect the flash habits: fireflies flash faster when it’s warmer and may engage in synchronous “flash-mob” displays when they gather in sufficient numbers. “It’s easy to overlook their diversity and complexity. You have to be curious and look closely.”
What Joyce describes as a “Morse code-like visual song” probably originated not as a beacon for love, but as a warning against predators. Just as brightly colored insects (Monarch butterflies and caterpillars) and amphibians (tropical dart-poison frogs) employ brilliant red, day-glo orange, acid yellow, and black coloration to escape becoming lunch, Joyce shares that “…current evolutionary thinking is that the flash originally meant ‘Stay away, because I don’t taste good,’” a theory confirmed by recent studies with bats, which quickly learn to avoid the appetizing but toxic flashing fireflies in flight.
A piece of amber found in Myanmar dates a fossilized ancestor of Lampyridae, the clade of insects to which fireflies belong, to the Late Cretaceous Cenomanian period, ninety-nine million years ago. Since then, the more than 2,000 identified species have inspired respect, even awe. For centuries in Japan, parks have been designated for the pleasure of viewing Hotaru, fireflies, which are traditionally revered as the spirits of fallen Samurai.
A piece of amber found in Myanmar dates a fossilized ancestor of Lampyridae, the clade of insects to which fireflies belong, to the Late Cretaceous Cenomanian period, ninety-nine million years ago. Since then, the more than 2,000 identified species have inspired respect, even awe. For centuries in Japan, parks have been designated for the pleasure of viewing Hotaru, fireflies, which are traditionally revered as the spirits of fallen Samurai. Ukiyo-e woodblock prints often portray women and children gathering the insects into translucent rice-paper lanterns. An exceptionally fine 14th-century sword, considered a national treasure and enshrined as a sacred object, was named Hotarumaru because damage inflicted upon the blade during battle was believed to have been repaired by fireflies while the Samurai owner slept. The meter-long original went missing after World War II, but the Hotaru legacy is so significant to Japanese culture that a museum-quality replica was created in 2019, the $436,376 cost covered by crowdfunding, primarily from members of the anime collective Touken Ranbu, a collectible card browser video game that celebrates images of young women wielding katana, or traditional swords.
Ukiyo-e woodblock image. — Courtesy of Wikimedia Commons
And yet the firefly may be in danger of quietly slipping out of sight without corrective human action. In addition to participating in The Firefly Atlas, Candace Fallon suggests simple steps to support firefly populations: rewilding a portion of a garden or yard; creating desirable dampness, shadows, and perching spots for larvae, ground-loving females, and juveniles; minimizing or rotating soil disturbance to allow juicy snails, slugs, and earthworms — favorite foods of fireflies — to proliferate; avoiding agricultural chemicals; planting shade trees; and refraining from introducing non-native species that may harm fireflies and their food-sources.
Then there’s the tricky one: reducing light pollution. Dark sky organizations estimate that approximately eighty percent of the earth’s inhabitants can no longer see the Milky Way, but diminished stargazing isn’t the worst of it. There’s substantial and growing evidence that artificial light at night is linked to the development of cancers in animals. Among other trials, a 2017 Harvard study, the Nurses’ Health Study II, argues persuasively that exposure to residential outdoor light at night may contribute to invasive breast cancer risk in humans.
The tentative conclusion is that light at night (LAN) disrupts circadian patterns and decreases the nocturnal secretion of melatonin. Ill effects of working at night are currently being scrutinized by science. Especially for people working aptly named graveyard shifts, evidence suggests that LAN increases risks for obesity, depression, sleep disorders, diabetes, and breast cancer. In particular, the blue light produced by LEDs (our multiple screens) and those energy-efficient compact fluorescent lightbulbs pose elevated danger to humans, according to experts at Harvard Medical School.
According to Avalon C.S. Owens, PhD, Tufts Institute of the Environment Fellow, the night sky has become 100% brighter during the past ten years, and the persistence of skyglow — the diffused haze produced by distant lights even in rural areas — plays a significant role in what entomologists call the coming Insect Apocalypse. The effect of light pollution on insects, she says, is a “giant blind spot” among fellow scientists.
Humans fear the dark. Without weapons, our naked-and-afraid ancestors were basically defenseless against stronger, faster nocturnal predators. Evolving lighting technology thus seemed like a godsend, first in fending off hungry carnivores, and then in allowing us to be active and productive (ah, progress!) around the clock. Will we ever go back to our campfires, beeswax candles, and smoky whale-blubber lamps? Not likely. But, Fallon says, “…just turning out your porch-light at night may help fireflies stabilize and survive.”
What You Can Do
- In the evening, draw your blinds and curtains so interior light does not spill outside.
- Turn off your porch light (or don’t use it at all).
- Leave some of your yard or garden “wild” to provide shelter for fireflies and glow worms.
- Don’t use pesticides, or even diatomaceous earth (the latter harms snails and slugs).
