Lighting up the darkness
By Mark H. Stowers
On a warm Michigan evening, just after the sky turns cobalt and before the mosquitoes lay their claim to the summer air, a familiar spark appears. Then another. Then a dozen. To children, fireflies are summer’s smallest fireworks bringing smiles and laughter and wonderment. To scientists, they are beetles in the family Lampyridae, insects with complicated courtship codes, surprisingly predatory young, and life cycles tied to soil moisture, wetland edges, dark nights, and the slow work of leaves breaking down underfoot.
Katie Hietala-Henschell’s work begins after sunset, when the air cools, the mosquitoes rise, and a field that looked ordinary by day starts blinking with messages. The Michigan Tech alum, endangered species conservation biologist for the Xerces Society for Invertebrate Conservation, grew up in southeast Michigan and now works with the organization’s firefly team to expand the Firefly Atlas, support firefly sanctuaries, and build conservation efforts across the central United States.
“My love for all insects has just grown over the last decade,” she said, describing a career that has moved through forest ecology, invasive species, rare-species surveys, and now fireflies.
For Hietala-Henschell, fireflies are not just a nostalgic summer pleasure. They are a conservation puzzle still being assembled.
“We still need a lot of baseline data and information on the full extent of firefly ranges,” she said. “New species are still being discovered.”
That uncertainty is part of what makes the lights in a Michigan yard both familiar and mysterious – scientists know enough to see trouble, but not always enough to measure it cleanly.
Fireflies or commonly referred to as lightning bugs, are not flies at all. They are soft-bodied beetles in the family Lampyridae, best-known for their bioluminescence – the chemical production of light. The answer to the age old question, “Daddy, why do their butts glow?” is a chemical reaction. Fireflies store Luciferin, a light-emitting compound in their lower abdomen. The enzyme Luciferase combines with the substrate Luciferin along with magnesium and ATP. When oxygen is introduced, the chemical reaction results in bioluminescence. The light is a “cold light” because the light produced is a visible light and not heat and the emitted flash is controlled by how much oxygen flows into the firefly’s light organs. Restricting the oxygen creates flashes and not a constant glow.
Around the world, more than 2,000 firefly species live in forests, wetlands, grasslands, mangroves, rice fields, stream corridors, dunes, and suburban yards. Hietala-Henschell said Michigan currently has “24 different firefly species” known from the state, though she cautions that number will likely change as surveys expand.
“With the currently available data, we don’t fully understand the full range of many firefly species and recent survey efforts are detecting populations outside of their previously understood range and resulting in new state records. It’s exciting to gain a better understanding of where species occur and this information will help inform conservation efforts,” she said.
In Michigan, Sarah Hughson, Ph.D., specialist in outreach and insect/arthropod diagnostician with Michigan State University Plant & Pest Diagnostics, estimates there are “about twenty or thirty species of fireflies.” Their glow may be nostalgic, but their future is not guaranteed.
The firefly life cycle is easy to miss because the famous adult stage is only the finale. Hietala-Henschell said adults live only “about two to four weeks,” but the larvae can live “about one to two years,” meaning fireflies spend most of their lives out of sight. After mating, females seek moist places such as leaf litter, downed logs or sphagnum moss to lay eggs so they do not dry out. Hughson explains that fireflies undergo “complete metamorphosis,” moving through “an egg stage, a larva stage, a pupal stage” and then the adult stage. The larvae hatch looking more like armored little alligators than the delicate adults people catch in jars, and they spend their time eating and growing.
“If we’re thinking about the whole life cycle of a firefly, it’s actually a pretty long-lived insect,” Hietala-Henschell said, “But it spends the majority of its life in the larval stage, just eating and growing.”
Only after this long juvenile period do larvae pupate in soil chambers, leaf litter or, in some species, on vegetation. As Hughson puts it, when insects are larvae, “their job is basically to eat and grow,” storing the energy they will need during the nonfeeding pupal stage. Once adults emerge, their main jobs are to mate, lay eggs and continue the cycle. Their short adult season helps explain why weather can make one summer seem brilliant and another strangely dim – a wet fall, mild winter, and wet spring can support larvae and their prey, while drought or habitat disturbance can suppress the show.
Firefly light is a language, and Hietala-Henschell said scientists often need that communication, also referred to as flash pattern, to identify a species.
“We really need their behavioral data,” she said, “Including the flash pattern, where they’re flying, what time they’re flying, and the color of the flash. In many flashing species, males fly above vegetation sending species-specific signals – single pulses, paired flashes, rising glows, or repeated patterns.”
Hughson says some species “will have different patterns that they use when they light up,” a system that helps them “recognize one another” and attract mates. Females often wait lower in the grass or on leaves, watching for the correct signal before answering. Their light also has an edge. Hughson notes that “there are also a couple of species where the female will mimic the pattern of other species so they can catch them and eat them.”
In other words, the same glow that courts a mate can also lure prey.
Sean Zara, wildlife program coordinator for Oakland County Parks and Recreation, adds that “All firefly larvae can glow, even in species whose adults do not use light to attract mates. Larval glow likely began as a warning signal because larvae are toxic or at least bad tasting. A way of telling predators, ‘you don’t want to mess with me.’”
Light pollution is a critical factor in the short life span of adult fireflies. Hietala-Henschell called it one of the major threats because it affects fireflies’ “ability to communicate,” along with other nocturnal insects and migrating birds. Porch lights, security lights, landscape lighting, sports fields, parking lots, streetlights, billboards, headlights, and the regional haze of skyglow can all interfere with courtship. A lawn may still look green by day, but if it is washed in light at night, it may be functionally unusable for species that communicate by flash.
Globally, fireflies are most diverse in warm, humid regions, but they occur across temperate and tropical landscapes. Southeast Asia is famous for synchronous fireflies that gather in mangroves and river corridors, where whole trees can pulse in rhythm. In Japan, fireflies are woven into cultural memory and seasonal festivals, yet some populations have been harmed by stream modification and water pollution.
The US is also home to synchronous fireflies, the most famous being Photinus carolinus (Synchronous Firefly) in the Great Smoky Mountains. This species is found in the Appalachian and Allegheny Mountains from as far south as Georgia and north into New York. To help protect populations from the negative effects of firefly tourism, the National Park Service and other stewards have implemented best practices such as using a lottery system to limit the number of visitors, minimizing the use of artificial light, and keeping visitors to trails and boardwalks to reduce disturbance to the ground where larvae are vulnerable to trampling. In Europe, glowworm species have declined in many areas as meadows, hedgerows, and dark rural lanes have changed. In North America, the flashing fields of the eastern United States are among the best-known displays, while western species may be less conspicuous or less dependent on flashing.
The common pattern is not that every firefly everywhere is disappearing at the same rate. It is that many species are vulnerable for similar reasons – they need intact habitat across their full life cycle, moisture for larvae and prey, dark nights for communication, and landscapes not saturated with broad-spectrum insecticides. Species with narrow ranges, specialized wetland or coastal habitats, aquatic larvae, or flightless females can be especially at risk because they cannot easily move when conditions deteriorate.
In the United States and Canada, researchers have begun turning anecdotes into assessments. Hietala-Henschell said The Xerces Society and partners helped conduct IUCN Red List conservation assessments for firefly species in the U.S. and Canada, and the results show both danger and uncertainty.
“Over half of the species assessed were data deficient,” she said. “Scientists do not yet have enough information to say how many firefly species are faring. When species of conservation concern are included, up to a third of the species in the US and North America appear to be threatened with some level of extinction.”
The Firefly Atlas was created to help fill those gaps by collecting observations, photographs, survey data, and habitat information from community scientists across North America. The largest U.S. threats mirror the global list – habitat degradation and loss, light pollution, climate change, pesticide exposure, poor water quality, invasive species, and physical disturbance of leaf litter, soil, wetlands, and shoreline vegetation. Hietala-Henschell puts habitat first.
“Habitat loss and degradation is probably the first, the biggest threat,” she said. “We’re still filling in wetlands when really, we shouldn’t be because they’re really hard to restore and create in other places.” Fireflies are not simply ‘yard insects.’ They are residents of layered habitat such as wet places, shaded places, unmowed edges, native plant communities, forest margins, marshes and damp meadows. Remove the layers, and the lights often go with them.”
Michigan is wholesome firefly country because it has the ingredients many species need – lakes, rivers, wetlands, damp woods, marshy fields, floodplains, roadside ditches, rain-soaked lawns, and long summer twilights. Hughson noted most Michigan fireflies, as larvae, live in “moist soils” near places such as wetlands, streams, ponds and lakes, where they feed on “soft-bodied animals” including earthworms, slugs and snails. Adults, she says, often favor grassy areas; some are predators, while many feed on pollen and nectar from flowers.
In some recent summers, Michiganders have reported unusually vivid firefly displays. Hietala-Henschell said the answer to whether numbers are declining is nuanced.
“We don’t have the data to say that outright,” she said, “Because long-term monitoring has not existed for fireflies the way it has for some other insects. Anecdotally, many people report seeing fewer fireflies, but some species appear to be doing well. The big dipper firefly, or common eastern firefly, is one example. We have that one in Michigan, and it’s the one you see in your yard. The last couple of years, they’ve been doing great.”
Hughson emphasizes that while insects are declining globally and fireflies are part of that broader concern.
“We don’t have any fireflies on the federal endangered species list,” Hughson explained.
Still, Michigan is not risk-free. Hietala-Henschell said that of the state’s 24 known species, “over a third” are either data deficient or species of conservation concern. Some may be rare; others may simply be poorly documented.
“That should be enough to get people to want to care,” she said.
One example of that uncertainty and risk is the Marsh Imp, a Michigan firefly tied closely to wetland habitat, according to Hietala-Henschell.
“One species of conservation concern in Michigan is Pyractomena lucifera, also known as the Marsh Imp. This species has been assessed as Data Deficient by the IUCN Red List Firefly Specialist Group and appears to have a decreasing population trend based on available data. It can be found across the central and eastern US and into Canada. This species is a wetland habitat specialist and found in marshes with aquatic vegetation and cattails. The Marsh Imp occurs in small populations making it susceptible to extreme weather events and development. One population that was studied in the 1970s appears to be extirpated, likely due to habitat loss. While data on direct threats for this species is lacking, we can infer likely threats based on the Marsh Imp’s life history. Two of the likely leading threats include habitat degradation, from development or changes in hydrology, and light pollution. Additional research is needed to better understand the effect of these threats, population size, and population trends. There are no protections or conservation strategies in place for this species and others like it,” she said.
The Marsh Imp is a smaller Pyractomena, typically measuring less than half an inch (9–10 mm), when compared to more common species such as Pyractomena borealis (Spring Treetop Flasher) or Pyractomena angulata (Say’s Firefly). The habitat it occupies and the flash pattern are essential pieces of information needed to identify this species. It gives a faint orange flash that repeats every five–seven seconds. In addition to being a marsh specialist and occurring in small numbers, this species is challenging to detect due to its short display period, typically occurring for up to an hour after sunset. In Michigan, it can typically be seen in late June through July.
Zara points readers toward the species many backyard observers are most likely to notice – the common eastern firefly, also known as the big dipper. It gets that name, he says, because “they flash and they make a little dip as they’re flying,” creating a small J-shaped signal for females.
Michigan is home to three common groups (or genera) of flashing fireflies. These are Photuris, Photinus and Pyractomena. Each genus contains several species with different life histories. Some of these species are relatively common and some of them are rare and experiencing decline. The rare ones are often habitat specialists or sensitive to certain threats. While fireflies at first glance look fairly similar across these three groups, there are some differences that can help people identify what fireflies are on their property and narrow it down to the genus level. Fireflies in the genus Photuris can range in size from medium to large (9-15 mm), typically have a greenish flash, and the markings on the head shield tend to consist of a clean black anchor, t-shape, or some variety in between. Species in the genus Photinus typically range in size from small to medium (7-12 mm) (with the exception of a couple larger species like Photinus pyralis and Photinus carolinus), give a yellowish flash, and have a dark spot or bar on their head shield. Fireflies in the genus Pyractomena range in size from small to large (7-15 mm), give an orange flash, and have a black triangle on their head shield with a diagnostic ridge.
Oakland County sits in a landscape where firefly needs collide with suburban habits. The county has lakes, ponds, wetlands, woodlots, parks, golf courses, stream corridors, and remnant farm fields – exactly the kinds of moist, mixed habitats fireflies can use. Zara says fireflies occur in “a lot of different high-quality habitats,” with some species acting as wetland specialists and others using different ecological niches. Oakland County also has expanding development, roads, lawn-dominated neighborhoods, bright exterior lighting, mosquito-control pressure, and invasive plant management challenges.
Oakland County also faces broader habitat issues common to southeastern Michigan – fragmented wetlands, stormwater runoff, shoreline hardening, deer browse pressure, invasive plants such as Phragmites and knotweed in some areas, and the gradual replacement of layered native vegetation with turf, mulch, and ornamental plantings. These changes may not target fireflies directly, but they simplify the damp, messy places where larvae hunt and adults display.
Zara noted Oakland County Parks and Recreation sees them as part of a larger conservation picture.
“If parks are protecting native habitats and rare habitat types, they’re probably going to do well if we’re doing everything else right,” he said. “Oakland County Parks does not manage specifically for fireflies, but they are part of a larger conservation picture. They’re probably going to do well if we’re doing everything else right.”
Fireflies are ecological neighbors, not just ornaments. Their larvae are predators that help regulate populations of slugs, snails, worms, caterpillars, mosquito larvae, blackfly larvae, and other small animals. Zara describes the larvae as “heavily armored,” flat, plate-covered insects with a “very heavy metal look,” crawling at ground level and actively hunting smaller prey.
Hughson offers a more cautious framing for their role in human terms – fireflies “don’t harm people, they don’t harm crops,” but they are also not always easy to classify as providing a direct economic service. Their value may be less agricultural than cultural, ecological and experiential.
Adults may also visit flowers, moving pollen incidentally as they feed or rest. More broadly, fireflies are indicators of habitat quality. Zara says they “seem to be indicators” of quality habitats, or at least places without heavy insecticide overspray. Their presence suggests that a yard, park, shoreline, or meadow is doing more than looking tidy. It’s functioning as habitat. He also sees a human benefit that should not be dismissed – fireflies “make people feel good” and may be “one of the first things that get kids interested in nature.”
For people and ecosystems, fireflies have few true disadvantages. They do not bite or sting in any meaningful way for humans, and they are not structural pests. Some adult fireflies prey on other fireflies, and some species contain defensive chemicals that make them unpalatable or potentially toxic to predators. That isn’t an ecosystem problem. It’s part of their natural role. The more practical concern is that people sometimes misunderstand firefly habitat as messy, mosquito-laden, or neglected. In reality, the leaf litter, tall grass patches, and damp edges that support fireflies also support many other beneficial insects, amphibians, birds, and soil organisms.
Light pollution – In developed parts of Michigan, nighttime light is one of the most fixable threats. Hietala-Henschell calls light pollution “the best kind of pollution” because “you can literally just stop it by turning a switch.” She recommends motion-sensor lights, timers, shielding exterior fixtures so light points only where needed, closing curtains in summer so indoor light does not spill outside, and using redder light where practical because it appears less disruptive to fireflies.
“Leaving artificial lights on at night can actually be detrimental to them,” Hughson says. Because fireflies use light as a form of communication to attract mates.”
Pesticides – Broad-spectrum insecticides used on lawns, gardens, ornamentals, crops, or for mosquito control can expose adults, larvae, prey, and wet soil habitats. Hietala-Henschell said fireflies are “just insects,” so insecticides aimed at other pests can still harm them. She urges landowners to avoid pesticide use, when possible, rely on mechanical removal or spot treatments where needed, and avoid whole-yard spraying. “A lot of times when we try to control for one type of insect, the insecticide that we use might kill other insects that we’re not intending to impact,” Hughson says.
Habitat simplification – Replacing wetlands, rough edges, meadow margins, and leaf litter with turf, hardscape, seawalls, sidewalks, parking lots and ornamental mulch removes shelter, moisture, display perches, and prey.
“Habitat loss can include the loss of woodland or wetland areas,” Hughson said. “The conversion of land to agriculture or urbanization, and more paved surfaces that block fireflies’ access to soil.”
Climate stress – Drought can dry soils and reduce prey. Heavy storms can alter wetland edges. Warmer winters and earlier springs can shift timing. Hietala-Henschell said climate change worries her because fireflies and their prey can suffer when larvae dry out under heat and drought, while extreme flooding can “scrape away habitats and wash them to a different place where the habitat isn’t suitable. Fireflies need that middle ground of not too dry and not too wet. Climate change can be especially relevant because fireflies really like to use moist soils.”
Water quality and invasive plants – Fireflies that depend on wet habitats can be affected by runoff, degraded shorelines, channelized drainage, and invasive plants that simplify habitat structure. Oakland County’s invasive species work highlights how local biodiversity depends on active stewardship of parks, roadsides, wetlands, and natural areas.
Helping fireflies is less about installing something special and more about stopping the habits that erase them. For lakefront owners, Hietala-Henschell’s first recommendation is simple – “turn off any unnecessary lights.” Landowners can begin with a broader rule – make part of the property darker, damper, softer, and more layered.
“There’s a lot homeowners can do,” she said. “Many actions don’t really cost a lot of money.”
Hughson’s simplest recommendation is also one of the easiest – “turn off the outdoor lights at night.”
Turn off unnecessary outdoor lights during firefly season, especially from dusk through late evening. Use warm-colored, shielded, downward-facing lights only where safety requires them. Reduce lawn area and allow patches of taller grass, sedges, native wildflowers, shrubs, and woodland edge plants.
Hietala-Henschell encourages property owners to be comfortable with “a little bit more of a messy yard,” because a short-cut turf monoculture may look clean but is “too sterile” for insect communities that evolved with native plants, leaf litter, moist soil and shelter. Leave some leaf litter, rotting logs, brush piles, and unmowed edges where larvae can shelter and hunt.
Hughson specifically recommends leaving “some wild habitat in yards,” including tall grass, logs and sticks.
“Leaf litter is a great overwintering site for different types of insects, including fireflies,” Hughson said.
Protect wetlands, rain gardens, pond edges, ditches, and low moist areas from mowing, filling, or chemical treatment. Avoid broad-spectrum insecticides and routine mosquito fogging whenever possible; Hughson recommends using insecticides only when they are actually needed and tolerating insects that are not harming people, crops, pets or property. Plant native vegetation of varied heights to create perches for flashing adults and habitat for prey.
Hietala-Henschell also recommends planting trees and native vegetation. Trees can help “make your own space darker,” she said, by filtering light from neighboring properties while giving adult fireflies cover during the day. Broad-leaved trees such as catalpa, sycamore and maple can provide daytime resting places. Manage stormwater with rain gardens, native buffers, and reduced runoff.
Record sightings with community science programs such as Firefly Atlas or Firefly Watch. Hietala-Henschell said the Firefly Atlas uses a no-kill survey protocol – participants catch a firefly, photograph the top and bottom against a scale, document the flash pattern and release it back where it was found.
Fireflies ask for a kind of restraint that runs against modern landscaping – fewer lights, fewer chemicals, fewer hard edges, fewer spotless lawns. They need the places between. The damp margin, the unmowed corner, the leaf-littered strip beneath shrubs, the dark shoreline, the native meadow that looks a little wild until the first flash appears. In return, they give more than beauty. They help regulate small prey, enrich backyard biodiversity, and remind us that a healthy night is not empty. It is alive, signaling.
In Michigan and Oakland County, the future of lightning bugs will be decided yard by yard and park by park. The good news is that many of the best actions are simple – turn off the patio lights, skip the pesticide treatment, leave some leaves, keep wet places vegetated, and let a portion of the property grow into layered habitat. If enough landowners do that, summer nights may keep their oldest language – a field speaking in sparks. And children’s wonder and amazement will continue for generations as they gaze into the Michigan skies and their own backyards.
