The Rarest of the Rare

by Diane Ackerman

  “There’s a firefly!” Tom calls, and he stalks it slowly, pouncing at the last moment to cage it in his hand.

  “Have a look,” he says, handing the insect to me.

  Holding its wings between my thumb and forefinger, I inspect the small lantern of its body, flashing a cold green light. It looks like the sight pilots long for late at night: the green rotating beacon of an airport. I slip the firefly into a small white-capped vial. It stops flashing. I tap the vial. It flashes again.

  “See, the flashing is a defensive thing,” Tom explains. “It produces one of the brightest cold lights ever devised. You can read by it.”

  A scintillation catches my eye and I turn to see a swarm of lights in a nearby tree. If we were looking at the sky through a telescope, it would be easy to confuse the firefly-bedecked tree with a glimpse of the Beehive nebula. Watching fireflies is one of the treats of summer nights. Because we’re not dark-adapted, they seem quite bright to us, but photographs barely catch a trace of them. Tom tells me that once, filming with the BBC, he gathered a whole mess of fireflies and threw them at a huge spiderweb (after he’d taken out the spider), and the cameraman filmed that spectacular cloud of fireflies. Children often share a sense of magic about fireflies. I’ve seen firefly auroras on my own front lawn in June. Eighteenth-century American women used to tie fireflies in their hair as decoration. I don’t know what they used as a tether. Sometimes we call them lightning bugs. Glow worms are the wingless ones that keep to the ground. But they’re all beetles belonging to the order Lampyridae, which have enchanted people of many countries. The ancient Chinese and Japanese both had firefly celebrations; Aristotle and Pliny described their habits. What songs would Solomon have sung to his beloved about her eyes flashing like fireflies? Because they’re not mentioned in the Koran, the Bible, or the Talmud, it’s probably safe to assume fireflies couldn’t survive in the Near East. But the story goes that they averted a war in Cuba: When the British generals Sir Robert Dudley and Sir James Cavendish arrived off Cuba, they saw what they thought to be the torches of belligerent Spaniards onshore. So they sailed to Jamaica instead.

  Fireflies flash by mixing two hypergolic chemicals. Unremarkable by themselves, these stuffs combine with a poetic flourish to build powerful, strange new substances. Nitrous oxide and glycerin, for example, produce the explosive nitroglycerin. In fireflies, the match includes luciferin and luciferase, and when they mix in the light organ under the firefly’s abdomen, they give off a yellowish-green light. We’re used to thinking of light sources as radiating heat, but these don’t. Actually, what they shed is oxygen, too much of which living things find as toxic as too little. Manufacturers have begun to take advantage of firefly dynamics by creating beacons, for trick-or-treaters or stranded motorists, which begin to glow when you mix the two chemicals together.

  “How can they do it so quickly—mix up those little beacons?” I ask.

  “How can you start a heartbeat suddenly? It’s amazing it was all done in six days, wasn’t it?” Tom says, with a wink in his voice.

  “Everything fun happened on the afternoon of the third day,” I reply. “Before that it was mainly darkness and light, afterwards bureaucracy.”

  “Good scientific method! If you’re going to have an important experiment, you don’t wait until the last day or you could screw the whole thing up.… Hey! Just look at that flash. Isn’t it wonderful!”

  For some time now, Tom’s been studying the “femme fatale fireflies,” in work he and his graduate student James Lloyd have made famous. As it turns out, males and females flash either when they’re hungry or when they want sex. In the flash-as-semaphore-of-lust scenario, the female waits on the ground or in the vegetation as she is barnstormed by a male. The male usually swoops down, and flashes for half a second while rising like a paintbrush stroke to make a J of light. If it’s his female, she’ll reply with a half-second flash. Then he’ll fly to her again and swoop-flash; she’ll flash back. What makes the luminous dance unique for the mates is the pause between the flashes. It’s as if the fireflies were reading the rests in a visual concerto. When they’re both reassured by this Morse code, they’ll mate. But some fireflies are femme fatales that lure other females’ mates by mimicking their flash code. When a male dives down, expecting to mate, the femme fatale eats him, not just from hunger or because she has a devilish streak, but because certain males carry defensive chemicals in their bodies. By eating such a male, the female saturates herself with a chemical armor that makes her distasteful to birds, spiders, and other predators. There’s enough heart stimulant in ten fireflies to kill a human being. So, armed and dangerous, mates rely on visual passwords during courtship. Everything is at stake. Because it takes a lot of energy to flash, they personalize the pause. What we see is a night decorated with their detailed yearnings and hesitations, a small opera in light.

  Elsewhere in the world—near rivers in Borneo and Thailand, for instance—there are “firefly trees” swarming with males that flash in unison to attract females from the forest. Along those midways, schooled in the neon of desire, females come to look for mates in the green-light district.

  “Have you seen the firefly trees?” I ask.

  “No, but I’m told they’re magical,” Tom says. “Isn’t it interesting how fireflies vary their courtship techniques? Different human cultures develop different traditions. The same thing is true with fireflies.”

  “You’d think the twinkling stars would confuse them.”

  “Their eyesight isn’t that good. Human settlements bother them, though—the air is different, the noise level, the lighting. There’s really very little human activity that’s compatible with the rest of the world,” he says with a sigh.

  I’m glad the dusk hides my slow smile. After all, Tom and Maria have raised three children and lived very much in civilization. I have as well. Part of the irony of environmentalism is questing for solutions when you know you’re part of the problem.

  The firefly in my hands flashes green with an afterglow of yellow.

  “I’ll tell you something that really blows my mind,” Tom says. “Nobody knows the life cycle of the common firefly.”

  “Why not?”

  “Because nobody knows where the larvae hang out. Can you imagine that? One of the most familiar insects in the world, and yet we’re still in the dark about it.”

  As we stroll back to camp, small eyes peer at us from the vegetation. Some animals have a mirrorlike membrane in their eyes that reflects light. If you aim a flashlight at the woods, you can often “shine” their eyes. This works with alligators as well as with spiders. Alligator eyes shine red, like two glowing cigarette butts; many spider eyes shine green. There are guidebooks to animal tracks, and even waterproof guides to reef dwellers, which you can take skin-diving with you, but I don’t know of any night guides to animal eyes.

  “Shining spiders” is a favorite pastime of night-prowling naturalists. Once, at an arts center on the east coast of Florida, attracted by eye shine, I found a six-by-ten-foot spiderweb stretching from my cottage roof to the porch steps. Its maker, a fawn-colored wolf spider, large as my fist, would take the web down each morning and reweave it each evening. She always left the guy wires in place, and spun slowly across the web like a hand moving over an autoharp. I named her Anna the Aranha, and often watched her build that gossamer radar net. When it was finished she would wait in a high corner, her green eyes shining, and when something vibrated the web, she knew just where to pounce. By night, the moon walked her silk; by day, the wind made it hum.

  Tom and I share a fondness for spiders. I like the way they weave and how they homestead the sky. Tom likes their dietary savvy, which makes them important to his trade. Spiders are his taste-testers. He feeds them all sorts of bugs, and if they refuse to eat one, he asks himself why. This is “why” with a capital W, the sort of question whose answer will lead to other questions and other answers, and be useful in chemical prospecting. Tomorrow we plan to
visit some of his royal taste-testers. So, bidding Tom good night, I return to the dormitory on the second floor of the main building and read a little before going to sleep. The book I’ve borrowed from a station intern is Leave Me Never, by Suzanne Carey, a steamy Silhouette Desire bodice ripper set at Archbold Station. Laughing at such sentences as “Before she could cry out or even speak, his other arm had come crushingly around her, pulling her up against the remembered male length of him,” I finally fall asleep, thinking about the codes of courtship preferred by humans and fireflies.

  After breakfast the next morning, Tom, Maria, Mark Deyrup (another entomologist), and I set out for Highland Hammock, an island of dense vegetation about an hour’s drive north. Because Tom is intrigued by the orange-and-brown-spotted ornate moth, which may contain a drug useful to humans, we’re going to do some experiments involving spiders. En route, we stop along the roadside and stroll in the brush, hoping to be lucky enough to find one of the endangered Tequesta scrub grasshoppers Mark is studying. This season he has already walked hundreds of miles along these highways and found precious few of them for study. A zebra swallowtail flutters across our path like a piece of newsprint, seemingly oblivious to the whoosh of traffic only a few yards away. The four-lane superhighway creates its own jet streams, transporting careless insects to who knows where.

  “I think I see one,” Maria calls. We hurry toward her with careful steps. Her keen eyes have zeroed in on a tiny twitch of black and white spots under a thatch of grass. The insect we’re searching for is wingless, but it can hop quite a distance, thanks to powerful leg muscles. Maria glues her gaze to the bouncing grasshopper, pointing at it, hop by hop, until Mark catches it in his hands.

  “Pretty big fellow,” he says, turning it over. “Actually it’s a female.”

  We huddle round him to have a closer look at the tiny black-and-white creature, which is both striped and spotted. In profile, it looks like a graph.

  “The female is larger than the male,” Mark explains, “and she tapers at one end. She lays her eggs underground, so she has these complicated little trowels at the rear end.”

  Bending down for a closer look, I follow her golden belly to a tiny pair of diggers. Then I look at the two compound eyes, surprised to discover black and white spots running right through them, too. Each domed eye is composed of hundreds of clear facets, in which the polka dots seem suspended.

  “One of the peculiar things about scrub grasshoppers,” Mark says, “is that they stay in coitus for many hours. You’ll see them hopping around together, attached.”

  “Ultimate togetherness,” Tom says. “They’re an item.” Maria laughs; it was only yesterday that Tom and Maria first heard that expression about a twosome and they like the late-breaking-news sound of it.

  “How long do they live?” I ask.

  “Almost a year,” Mark says as we climb into the car, put the grasshopper safely away, and continue our drive. “But it’s hard to study their relationships because ridges of scrub are sometimes isolated from each other by highways, housing tracts, orange groves. But grasshoppers seem to change genital shape very readily, and we can use that to identify which ones have been living close together and which ones have traveled. See, with insects, there’s something called runaway evolution. Genitals change very fast within a group. It’s apparently based on female preference. One group will develop a few little extra prongs on the male genitalia, although there’s nothing particularly adaptive about them.”

  “If they don’t help the animal adapt to its environment, why do they develop?”

  “Just because the females like them. A little prong starts for some reason; the females prefer the prongs and mate with those males; and the offspring carry genes for prongs. You know, it may not be too different from the way the Irish elk became extinct—because the females kept saying, ‘I don’t want you until you get even bigger antlers.’ Ultimately, the antlers got too big to carry.”

  One might wonder why female grasshoppers prefer the prongs in the first place. But nobody really knows. One theory is that it’s very important for females to know that they actually have mated. The males have to transmit clearly the message that copulation has taken place. Among insects, copulation often gets interrupted by predators, weather, and so on. So it’s important that both partners realize sperm has been transferred. If a male stimulates a female using a lot of ballyhoo or a novel design, he’ll succeed in procreating, because the female will be absolutely sure copulation took place and will therefore reject other males. There’s no point in her spending a lot of time mating if it’s not necessary. These genital changes become extraordinarily elaborate and can involve bundles of hair, little growths of hooks, peculiar reversible sacs with hairs on the end, and unusual knobs that point in opposite directions. They’re adaptive only in the sense that they assure the female that she’s mating with a male of the right species, but they have no external use at all. They’re just decorative. So, it’s highly unlikely that different species would develop exactly the same genitals. This fact alone allows scientists to trace the relatedness of organisms and their habitats.

  “Tom and I are very different entomologists,” Mark continues. “A lot of his work has an old-fashioned natural-history base, but he’s in the vanguard of what’s being discovered now. Almost nothing that I do couldn’t have been done a hundred years ago.”

  “Both of us have been dragged kicking and screaming into the nineteenth century,” Tom corrects him.

  “No, my kind of work is catching-up work. A lot of the natural-history and survey studies that took place in Europe in the eighteen-hundreds were never done in Florida. People were busy doing other things. So I spend a lot of time just listing insects, finding out where they live, how they live. It’s not something that you can be paid to do.”

  When we think of science, we often picture arcane quests after minutiae, or efforts to explain underlying principles. But it’s amazing that in a civilization as complex as ours, we are still engaged in Adam’s task, the naming of the animals.

  “There are very few places where you can actually look at a whole ecosystem and say how many of something live there,” Mark says. “At the station, we’re beginning to be able to do that. We’ve just put together a new moth-and-butterfly list, for instance, with more than eleven hundred species on it. And there’s another five hundred or so species to be identified—that’s just moths and butterflies! We have roughly nine hundred species of beetles listed, but we assume there are about two thousand. And the ants, bees, and wasps probably make up an even larger group. We’ve listed about one thousand flies. So the total number of different kinds of insects in Archbold’s small habitat is about ten thousand. And that’s nothing compared with what you’d find in a deciduous forest. The Endangered Species List is barely a start. Most insects aren’t even known. So how can we tell which ones are endangered?”

  Soon we arrive at Highland Hammock, a state park. As we walk along carefully laid-out pathways, we enjoy the primal feel of the dense forest, which contains a mix of northern and southern trees: vast woods of sweet gums and hackberries, red maples, hickories, and live oaks and pines. Flowering poison ivy vines twenty feet long hang from branches, with Spanish moss, epiphytes, and orchids. Flexing open a broad palmetto leaf, I see four species of moths, whose caterpillars are feeding on the leaves; wasp and fly parasites that attack the caterpillars; miscellaneous spiders, which coexist perfectly well with the moth caterpillars; parasites that attack the spiders; small millipedes; yellow ants; and fly maggots. On this one leaf, three feet above the ground, a complex ecosystem thrives. These are not creatures that one would find in the normal leaf litter on the forest floor, which is filled with other spiders, ants, and centipedes and is a dangerous place to live. Instead, these insects raise their generations on a sort of penthouse forest floor. It’s odd to think of there being a specialized habitat no larger than a palmetto leaf.

  “Aha!” Tom calls gleefully.

 
; We find him up the road a few yards, happily inspecting a huge spiderweb, billowing at eye level between two trees. A big furry spider with a crazy-eight-shaped body and eight many-knuckled legs sits in the upper-right-hand corner of the web. Tom takes a vial out of his pocket, pulls an ornate moth from it, and tosses the moth onto the web. In a flash, the spider rappels down the silk and cages the moth in its legs.

  “So much for the moth,” I sigh.

  “Wait.” Tom raises a cautionary finger, as the spider begins cutting the moth loose from the web, using sharp fangs at either side of her mouth. “See, she’s decided she doesn’t want it. See how she backed away? Now the question is how she will treat it. She’s cutting—see the cutting? There are two palps, which are like two short hands around the mouth—if we had palps, we could eat and play music at the same time!—and she’s taking the thread with those two palps and putting it in her mouth. It’s going to be cut loose in a second. Now she’s starting to pull back so the moth doesn’t damage more of the web.”

  The spider cuts a perfect window in the web with her sharp fangs. Playing doggo, the moth finally falls free and takes flight. Then the spider returns to her watch at the top of the web.

  “Good heavens. Why did she do that? I thought spiders liked moths.”

  “Only edible ones,” Tom says.

  “Even so, why clip it from the web?”

  “Because the spider can’t see everywhere at once on a big web. So she takes the high ground and waits. When something vibrates the web, she can read the vibrations to tell exactly where it is. But if her web is cluttered with debris, she’ll get a faulty signal.”