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What Makes Fireflies Glow?

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When ancient humans saw mysterious blinking lights over field and stream, they sometimes attributed the light to dragons, gods or demons. Reports in early religious writings from China and India hold the earliest recorded discovery of the true source of the lights. The glow came not from deities or monsters, but normal, mortal animals: fireflies.

Greek and Roman scholars made the first thorough examinations of fireflies (which aren’t actually flies, but a family of beetles known as Lampyridae) and other “luminous organisms.” Aristotle described almost 200 marine species with the strange power to glow.

Centuries later, the phenomena of bioluminescence (from the Greek bios (“living”) and the Latin lumen (“light”))was fairly well known, but still poorly understood. While Shakespeare mentioned the “effectual fire of the glow-worm” in Hamlet, English explorers missed their chance to land on a poorly defended Spanish Cuba, mistaking fireflies for Spanish campfires and deciding they would be outnumbered.

In 1887, French pharmacologist Raphael Dubois made a giant leap in figuring out the secrets of bioluminescence.

During one of his experiments, he took tissues from a bioluminescent clam called the common piddock and ground them up. He found that if he put the ground tissues in cold water, they glowed for a few minutes. He’d extracted the animal’s light-producing chemicals. When he put ground tissues in hot water, there was no glow, but adding the hot water to the cold water made the light come back on. He called the hot water extract luciferin (from Lucifer, Latin for “morning star”) and the cold water extract luciferase.

American biologist Edmund Newton Harvey continued on the path that Dubios had forged and spent most of his career looking for luciferin and luciferase in almost every luminous organism he could find. He discovered that luciferins and luciferases from different animals were not interchangeable; he hypothesized this was because bioluminescence and its systems had evolved to fit the various needs of different species.

You Light up My Life: The How’s and Why’s of Bioluminescence in Fireflies
The tag team of the luciferase enzyme and the luciferin molecule is the key to turning on a firefly. To make light, luciferin combines with adenosine triphosphate (ATP), a high-energy molecule that powers cells, to form luciferyl adenylate and pyrophosphate. These compounds bind to the surface of luciferase. Luciferyl adenylate then combines with oxygen to make the molecules oxyluciferin and adenosine monophosphate (AMP). Rapid energy loss from the excited oxyluciferin results in it giving off visible light.

The wavelength of this light is between 510 and 670 nanometers, making it appear like a pale yellow or orange-green color to us. In the area of the body where the light-making reaction happens—called the photic organ or the lantern—there are uric acid crystals that help reflect the light away from the abdomen.

How fireflies control their glow is still a mystery. There are several competing hypotheses that point to oxygen intake, messages from the brain, and other methods for controlling the lantern. However fireflies turn their light on and off, scientists do know what the glow is for: love and war.

For firefly larvae, bioluminescence is a defense against predators. Most firefly larvae produce chemicals within their bodies that are toxic—or at least taste terrible. Their glow warns predators that they won’t be a pleasant meal, and that trying to eat them isn’t going to do anyone any good.

Biologists think adult fireflies used to also use their glow for defense, but it eventually evolved as a tool for mate selection and communication. At certain times of night when they’re active, male fireflies will begin flashing a light pattern specific to their species. Females of the same species will watch and if a flashing male catches a female's eye, she will respond with the same pattern, on a short time delay. A flash dialogue ensues as the male locates his lady fair and flies to her to begin mating. Female fireflies are known to be fond of certain flash characteristics, like longer flash duration and bigger lanterns, and will preferentially respond to and mate with males who have more attractive glows.

Males looking to mate walk a thin line between sex and death every time they flash their light. Females of the Photuris genus of North American have figured out how to turn amorous males into an easy meal. They’ve developed an ability to replicate the mating flash code used by the Photinus genus. The Photuris females will flash back their hacked code in response to males, and when the poor suckers come looking for some loving, they walk into a dinner date that won’t end well.

Not only do the femme fatales get a meal, but they also pick up an insurance policy against getting eaten themselves. Photinus fireflies have a natural defense against predators in the form of steroidal chemicals called lucibufagins, which Photuris fireflies lack. When a female Photuris cannibalizes a male Photinus, though, the toxins slip into her bloodstream. She’s now got a defense against hungry predators and can even pass the protective chemicals onto offspring.

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Getty Images (Johnson) / iStock (ghosts)
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History
When Lexicographer Samuel Johnson Became a Ghostbuster
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Getty Images (Johnson) / iStock (ghosts)

Dr. Samuel Johnson is today best known for his Dictionary of the English Language (1755), which remained the foremost authority on the English language until the Oxford English Dictionary appeared more than a century later. The dictionary took Johnson nine years to complete, for which he was paid the princely sum of 1500 guineas—equivalent to $300,000 (or £210,000) today. Although it wasn’t quite the commercial success its publishers hoped it would be, it allowed Johnson the freedom to explore his own interests and endeavors: He spent several years editing and annotating his own editions of all of Shakespeare’s plays, and traveled extensively around Britain with his friend (and eventual biographer) James Boswell—and, in 1762, helped to investigate a haunted house.

Johnson—who was born on this day in 1709 and is the subject of today's Google Doodle—had a lifelong interest in the paranormal, once commenting that he thought it was “wonderful” that it was still “undecided whether or not there has ever been an instance of the spirit of any person appearing after death. All argument is against it, but all belief is for it.” According to Boswell, however, he was more of a skeptic than an out-and-out believer, and refused to accept anything without seeing the evidence for himself. So when the news broke of an apparently haunted house just a few streets away from his own home in central London, Johnson jumped at the chance to perhaps see a ghost with his own eyes.

The haunting began in the early 1760s, when a young couple, William and Fanny Kent, began renting a room from a local landlord, Richard (or William—sources disagree, but for clarity, we'll use Richard) Parsons, at 25 Cock Lane in Smithfield, London. Soon after the Kents moved in, Richard’s daughter, Betty, began to hear strange knocking and scratching sounds all around the house, and eventually claimed to have seen a ghost in her bedroom.

Richard soon discovered that William was a widower and that Fanny was in fact his deceased wife's sister; under canon law, the pair couldn't be married, and Richard became convinced that the ghost must be that of William's deceased first wife, Elizabeth, blaming William’s presence in the house for all of the strange occurrences. He promptly evicted the Kents and the noises soon subsided—but when Fanny also died just a few weeks later, they immediately resumed and again seemed to center around Betty. In desperation, a series of séances were held at the Cock Lane house, and finally Fanny’s ghost supposedly confirmed her presence by knocking on the table. When questioned, Fanny claimed that William had killed her by poisoning her food with arsenic—an accusation William understandably denied.

By now, news of the Cock Lane Ghost had spread all across the city, and when the story broke in the press, dozens of curious Londoners began turning up at the house, queuing for hours outside in the street hoping to see any sign of supernatural activity. According to some accounts, Parsons even charged visitors to come in and “talk” to the ghost, who would communicate with knocks and other disembodied noises.

But with the suspicion of murder now in the air, the Cock Lane haunting changed from a local curiosity into a full-blown criminal investigation. A committee was formed to examine the case, and Johnson was brought in to record their findings and investigate the case for himself.

On February 1, 1762, one final séance was held with all members of the committee—Johnson included—in attendance. He recorded that:

About 10 at night the gentlemen met in the chamber in which the girl [Betty] supposed to be disturbed by a spirit had, with proper caution, been put to bed by several ladies. They sat rather more than an hour, and hearing nothing, went down stairs, when they interrogated the father of the girl, who denied, in the strongest terms, any knowledge or belief of fraud … While they were enquiring and deliberating, they were summoned into the girl’s chamber by some ladies who were near her bed, and who had heard knocks and scratches. When the gentlemen entered, the girl declared that she felt the spirit like a mouse upon her back.

But the committee were suspicious. Betty was asked to hold out her hands in front of her, in sight of everyone in the room:

From that time—though the spirit was very solemnly required to manifest its existence by appearance, by impression on the hand or body of any present, by scratches, knocks, or any other agency—no evidence of any preternatural power was exhibited.

Johnson ultimately concluded that it was “the opinion of the whole assembly that the child has some art of making or counterfeiting a particular noise, and that there is no agency of any higher cause.” And he was right.

As the investigation continued, it was eventually discovered that Richard Parsons had earlier borrowed a considerable amount of money from William Kent that he had no means (nor apparently any intention) of repaying. The two men had a falling out, and Parsons set about elaborately framing Kent for both Fanny and Elizabeth's deaths. The ghostly scratching and knocking noises had all been Betty’s work; she hidden a small wooden board into the hem of her clothing with which to tap or scratch on the walls or furniture when prompted.

The Parsons—along with a servant and a preacher, who were also in on the scam—were all prosecuted, and Richard was sentenced to two years in prison.

Although the Cock Lane haunting turned out to be a hoax, Johnson remained open minded about the supernatural. “If a form should appear,” he later told Boswell, “and a voice tell me that a particular man had died at a particular place, and a particular hour, a fact which I had no apprehension of, nor any means of knowing, and this fact, with all its circumstances, should afterwards be unquestionably proved, I should, in that case, be persuaded that I had supernatural intelligence imparted to me.”

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The King of Kong © Jim Naughten. Courtesy of Michael Hoppen Gallery
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geography
The Mountains of Kong: The Majestic West African Range That Never Existed
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The King of Kong © Jim Naughten. Courtesy of Michael Hoppen Gallery

If you look closely at a 19th century map of Africa, you’ll notice one major way that it differs from contemporary maps, one that has nothing to do with changing political or cartographical styles. More likely than not, it features a mountain range that no longer appears on modern maps, as WIRED explains. Because it never existed in the first place.

A 19th century map of West Africa
From Milner's Descriptive Atlas, 1850

The “Mountains of Kong” appeared on almost every major commercial map of Africa in the 1800s, stretching across the western part of the continent between the Gulf of Guinea and the Niger River. This mythical east-west mountain range is now the subject of an art exhibition at London’s Michael Hoppen Gallery.

In "Mountains of Kong," stereoscopic images by artist Jim Naughten—the same format that allowed Victorians with wanderlust to feel like they’d seen the world—reveal his view of the world of wildlife that might have existed inside the imagined mountains. As the gallery describes it, “he imagines a fictitious record made for posterity and scientific purposes during an expedition of the mountain range.” We’ve reproduced the images here, but to get the full effect, you’ll have to go to the gallery in person, where you can view them in 3D with a stereoscope (like the ones you no doubt played with as a kid).

Toucans fight a snake in two almost-identical side-by-side images.
The Toucans © Jim Naughten. Courtesy of Michael Hoppen Gallery

Naughten created the images by taking two photographs for each, and moving the camera over some 3 inches for the second photo to make a stereoscopic scene. The landscapes were created by shooting images of Scottish and Welsh mountains and dioramas in natural history museums, using Photoshop to change the hues of the images to make them seem more otherworldly. His blue-and-pink-hued images depict fearsome apes, toucans sparring with snakes, jagged peaks, and other scenes that seem both plausible and fantastical at the same time.

The Mountains of Kong appeared in several hundred maps up until the 20th century. The first, in 1798, was created by the prominent geographer James Rennell to accompany a book by Scottish explorer Mungo Park about his first journey to West Africa. In it, Park recounts gazing on a distant range, and “people informed me, that these mountains were situated in a large and powerful kingdom called Kong.” Rennell, in turn, took this brief observation and, based on his own theories about the course of the Niger River, drew a map showing the mountain range that he thought was the source of the river. Even explorers who later spent time in the area believed the mountains existed—with some even claiming that they crossed them.

Two colobuses stand in a tree on a mountaintop.
The Colobus © Jim Naughten. Courtesy of Michael Hoppen Gallery

The authority of the maps wasn’t questioned, even by those who had been to the actual territory where they were depicted as standing. Writers began to describe them as “lofty,” “barren,” and “snow-covered.” Some said they were rugged granite peaks; others described them as limestone terraces. In almost all cases, they were described as “blue.” Their elevation ranged from 2500 feet to 14,000 feet, depending on the source. Over the course of the 19th century, “there was a general southward ‘drift’ in the location,” as one pair of scholars put it.

Though geographers cast some doubt on the range’s existence as time went on, the Mountains of Kong continued to appear on maps until French explorer Louis-Gustave Binger’s Niger River expedition between 1887 and 1889, after which Binger definitively declared their nonexistence.

By 1891, the Mountains of Kong began dropping off of maps, though the name Kong still appeared as the name of the region. By the early 20th century, the mountains were gone for good, fading into the forgotten annals of cartographic history.

[h/t WIRED]

All images courtesy Michael Hoppen Gallery.

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