Chapter 1: The Legacy of the Invisible

I hail from a lineage of naturalists and scientists, where every few generations, a family member emerges who can perceive the unseen. In the mid-20th century, that individual was me. As a young child, I expressed frustration to my granduncle Erasmus — my predecessor in spotting these elusive beings — that since no one wanted to accompany me in capturing invisible beetles, I wished to see only what other children could see. Through a haze of cigar smoke, Granduncle replied, “And what if Leeuwenhoek had wished to see only what others saw?”

I countered that Leeuwenhoek had a microscope, while I lacked the means to make others perceive what I could. They didn’t look intently; they didn’t care; they laughed at me. My distress must have been evident, as Granduncle’s imposing moustache loomed closer, carrying the scent of ashes and leather. I noted the peculiar hairs dancing in his nostrils, carried on his breath like tiny feathers.

“It’s not about how hard you look, Sophie. It’s about how you perceive.” His tusky smile accompanied this wisdom, which has since fueled my writing about the invisible creatures I study — beings recognized only by other unseen entities (and, fortunately, by me, for science). I write to share my unique perspective, as Granduncle advised. In essence, I see connections between the unseen animal life and human existence. I might even suggest that we humans are the most invisible of creatures, as we often fail to recognize our own animal nature. To truly understand ourselves, we must confront the unseen aspects of our lives — ourselves and others.

One particularly intriguing case I've examined is that of a firefly species whose generations alternate between visibility and invisibility every 29 years, leading to dire consequences for humanity.

Chapter 2: The Dazzling Beacon Bugs

The poet John Milton once sang, “Hail holy Light.” Who doesn't crave illumination in a shadowy world? Yet, Beacon Bugs prefer darkness. This native firefly species has a remarkable characteristic: for 28 years, they remain invisible to the human eye, quietly mating and passing away without our notice. However, in the 29th year, they produce a visible generation that outshines all others; it is astonishingly brighter and noticeable to the untrained eye. This rare generation of Beacon Bugs becomes a mesmerizing spectacle, a dazzling beacon that reminds us that an invisible firefly is an oxymoron — if you emit light, you ought to be seen. At this point, humanity becomes aware of their presence and faces the repercussions.

To truly grasp the impact of Beacon Bugs on our lives, one must understand the fundamental traits shared by most fireflies. Fireflies attract partners by emitting light in distinct patterns of flashes and steady glows, which serve as codes signaling that two fireflies belong to the same species. However, these codes, while effective for attracting mates, also render them susceptible to predation by cannibalistic fireflies of the genus Photuris. The methods by which Photuris takes advantage of other fireflies' signals will soon be discussed. For now, it is sufficient to note that among the approximately 2,000 firefly species found in environments ranging from Malaysia to the Great Smoky Mountains, only one species employs invisibility as a defense mechanism against Photuris: the Beacon Bugs. Unfortunately, their unique strategy of invisibility can sometimes prove more detrimental than being preyed upon by Photuris.

All fireflies embody a romantic essence. They cannot be bred in laboratories, just as love cannot be manufactured. During courtship, the male offers a nutritious gift to his mate (call it chocolate, if you will). The couple lays their eggs on the ground without constructing nests, embodying their free-spirited nature, while the larvae burrow underground, transforming into glow-worms that carry the torch of firefly lineage from the moment they were mere glimmers within their parents.

The mating ritual of fireflies is a North American tradition, contrasting with the more sedate courtships of their Old World counterparts. Here, each male embarks on a solo evening journey, flashing his lights over lawns at dusk. You observe glimmering ribbons of fireflies floating a few feet above the grass, tracing love letters against the twilight sky, seeking a mate whose enticing form lies hidden in the dimness. In this enchanting moment, you may overlook the lurking nightmare.

A male firefly flits across the tops of towering grasses, signaling his lights, coded for the exhilarating moment when a female, receptive and eager, responds in kind. After a scintillating exchange, he descends to meet her. She swiftly flips him onto his back, pinning him down with her six delicate feet — she is larger than him — and begins to devour him with her sharp mandibles. Her antennae quiver with hunger; the sound of her feasting resonates through the grass. Poor lovesick bug! He has not mated or reproduced; he perishes. To her, he was merely a meal.

Chapter 3: The Cycle of Life and Death

This gruesome act is known as “aggressive mimicry.” Female Photuris fireflies imitate the mating flashes of other species to ensnare and consume unsuspecting males. Photuris is a true horror, a merciless predator, and the ultimate femme fatale. To attract a female of his own species, the Photuris male must deceive her by mimicking the flashes of another species’ male — only then can he reveal his identity while keeping a safe distance. If he is particularly cunning, he may even imitate the female of another species, luring both unsuspecting males and the ravenous Photuris female.

Why don’t the targeted fireflies adjust their mating signals? Well, they do. North American fireflies continuously modify their luminous codes, yet Photuris remains an unyielding mimic, thriving on the thrill of cracking codes before dinner. Reader, gaze upon your evening lawn, where it sparkles and glimmers! It’s a sea of love, crisscrossed by deceitful predators, sowing confusion and death through the pure medium of light. Though it’s July, don’t your bare feet feel cold?

Beacon Bugs have adopted the most extreme self-defense strategy: their periodic invisibility. For 28 years, they remain unseen by Photuris and other visible predators, refraining from glowing. As I have the privilege of observing these invisible Beacon Bugs, I can confirm that without their lights, they are extraordinarily inconspicuous. They resemble a slimy piece of tobacco, shrouded in leathery elytra, as if the object had solidified in a neglected spittoon.

With their lights extinguished, the first invisible generations experience a population surge, shielded from the predation of Photuris and her partners. My data sighs with relief. Yet, puzzlingly, rather than stabilizing, the Beacon Bug population begins to decline. The final invisible generation is so sparse it’s nearly wiped out. Why would a potent defense strategy coincide with the decline of the very species it safeguards?

Several hypotheses emerge. A firefly’s flash can deter predators averse to being blinded by their meal. By adopting a strategy of lightlessness, Beacon Bugs may inadvertently attract new predators. Invisible creatures can perceive one another; during spring, for instance, the world is awash with invisible frogs and toads, lacking the charming princes of fairy tales. There’s no such thing as a free lunch, especially if you become the meal.

Another hypothesis may more adequately explain this gradual decline. Like many fireflies, Beacon Bugs spend a significant portion of their lives in larval form underground. A great deal can change in that time: a meadow can be paved, excavated, or flooded. When the adult Beacon Bugs finally emerge, they may struggle to locate one another — have you ever tried to navigate an unfamiliar neighborhood at night without headlights? Perhaps the newly adult Beacon Bugs face challenges in reuniting, leading to their fragmentation into smaller, more vulnerable groups.

Reflecting on the 2011 scandal surrounding the wreck of the luxury sloop Folly in Lake Erie, one might wonder about the accuracy of perception. The Folly ran aground due to hull failure, taking with it the lives of its owner, Hoagland “Hog” Makemerry, and his young wife, Tipple. During the televised trial that followed, the skipper maintained he had been steering toward the Toledo harbor light — a claim deemed absurd, as the Folly was far too distant to have seen it. Laughter erupted from audiences spanning Cleveland to Detroit.

Yet I suspect the Folly’s skipper was not inebriated but genuinely saw a lighthouse beam that shouldn’t have existed. Consider this curious phenomenon surrounding shipwrecks in Lake Erie: a ship sinks almost precisely every 29 years — the sandsucker Isabella Boyce in 1917 and the teak barquentine Success in 1946, among others. I wouldn’t be surprised if this pattern extends across the nation, wherever sailors recount tales of phantom lights that lead ships to disaster, in meadows and marshes where fireflies emerge.

What likely transpired that fateful night? It was a cloudy, moonless evening when the Folly followed the beam cutting through the darkness, a guiding light her skipper instinctively trusted. Who would question such a light, one that resonates with our understanding, beckoning us home? The skipper could not have foreseen the spectacle occurring in the pitch black ahead, where swarms of male Beacon Bugs coalesced in their thousands, pulsing on and off in unison.

Even if he had been a boy who captured fireflies in a jar, releasing them to flash along with his flashlight, how could he imagine that a sky-high swarm of Beacon Bugs was echoing the Toledo light’s beam and rhythm? Through that tragic night, the massed cloud of male Beacon Bugs, desperate for connection, broke their concealment and emitted the brightest signals they could muster. To any ship passing by, it appeared as the beckoning light of harbor and home.

Thus, the wreck of the Folly became collateral damage in the cycle of the Beacon Bugs, a revolution that unfolds every 29 years. It may seem ironic to label a periodic event a revolution, yet as long as revolutions continue to occur in the ceaseless passage of time, there is no irony in acknowledging their awe-inspiring spectacle and their inherent mystery. How could any of us, including the captain of the Folly, grasp the urges that drive a generation to rebel against the wisdom of their shadowy predecessors, igniting themselves amid the darkness, mimicking the brightest light in their universe?

Desire reinvents the wheel, and though the wheel may remain ever-changing, the subtle differences accumulate to form hope. Along the shores, female Beacon Bugs congregate in their multitudes, responding to the signals of love transmitted from earth to sky and vice versa. Meanwhile, Photuris, the eternal predator, the relentless enemy of all new beginnings, delightedly adds a long-missed item to her menu.

On the treacherous rocks of Niagara Reef lies a gold compact, once held in the hands of poor Tipple Makemerry. It used to reflect a human face, now it mirrors the cold assembly of the Pleiades. The desire for light, the betrayal by light — how unsettling it seems, yet how fitting and natural it is.

Sharona Muir is a recipient of the National Endowment for the Arts Fellowship and has published work in Granta, Orion, and various other publications. She is the author of The Book of Telling. This narrative has been adapted from Invisible Beasts: Tales of the Animals that Go Unseen Among Us Copyright © 2014 by Sharona Eve Muir.