Scientists have identified 2 million species of living things. No one knows how many more are out there, and tens of thousands may be vanishing before we have even had a chance to encounter them. By Jacob Mikanowski
The Earth is ridiculously, burstingly full of life. Four billion years after the appearance of the first microbes, 400m years after the emergence of the first life on land, 200,000 years after humans arrived on this planet, 5,000 years (give or take) after God bid Noah to gather to himself two of every creeping thing, and 200 years after we started to systematically categorise all the world’s living things, still, new species are being discovered by the hundreds and thousands.
In the world of the systematic taxonomists – those scientists charged with documenting this ever-growing onrush of biological profligacy – the first week of November 2017 looked like any other. Which is to say, it was extraordinary. It began with 95 new types of beetle from Madagascar. But this was only the beginning. As the week progressed, it brought forth seven new varieties of micromoth from across South America, 10 minuscule spiders from Ecuador, and seven South African recluse spiders, all of them poisonous. A cave-loving crustacean from Brazil. Seven types of subterranean earwig. Four Chinese cockroaches. A nocturnal jellyfish from Japan. A blue-eyed damselfly from Cambodia. Thirteen bristle worms from the bottom of the ocean – some bulbous, some hairy, all hideous. Eight North American mites pulled from the feathers of Georgia roadkill. Three black corals from Bermuda. One Andean frog, whose bright orange eyes reminded its discoverers of the Incan sun god Inti.
About 2m species of plants, animals and fungi are known to science thus far. No one knows how many are left to discover. Some put it at around 2m, others at more than 100m. The true scope of the world’s biodiversity is one of the biggest and most intractable problems in the sciences. There’s no quick fix or calculation that can solve it, just a steady drip of new observations of new beetles and new flies, accumulating towards a fathomless goal.
But even as thousands of new species are being discovered every year, thousands more seem to be disappearing, swept away in an ecological catastrophe that has come to be known as the sixth extinction. There have been five such disasters in the past. The most famous (and recent) is the end-Cretaceous extinction, the one that killed off the dinosaurs 66m years ago. The most destructive was the Permian, the one that cleared the way for the dinosaurs 190m years before that.
To know if we are really in the midst of a sixth extinction, scientists need to establish both the rate at which species are currently vanishing, and the rate at which they would go extinct without human activity (known as the “background rate”). In 2015, using a census of all known vertebrates, a team of American and Mexican scientists argued that animal species are going extinct “up to 100 times” faster than they would without us – a pace of disappearance on a par with the extinction that took out the dinosaurs.
But as Terry Erwin, the legendary tropical entomologist, pointed out to me, these sixth-extinction estimates are “biased towards a very small portion of biodiversity”. When it comes to invertebrates – the slugs, crabs, worms, snails, spiders, octopuses and, above all, insects that make up the bulk of the world’s animal species – we are guessing. “Conservationists are doing what they can, without data on insects,” he said.
To really know what’s going on with the state of the world’s biodiversity, ecologists need to start paying more attention to the invertebrates and spend less time on the “cute and cuddlies” – Erwin’s term for the vertebrates. (Years of hearing about the wonders of gorillas and humpback whales can make a staunch bug man resentful.) After all, there are far, far more of them than there are of us.
We live in an invertebrate world. Of all known animal species, less than 5% have backbones. About 70% are insects. Fewer than one in every 200 are mammals, and a huge proportion of those are rodents. Looked at from the point of view of species diversity, we mammals are just a handful of mice on a globe full of beetles. The great majority of those beetles are herbivores native to the tropics. So if you really want to understand the total diversity of life on Earth – and the true rate at which it is disappearing – you need to figure out how many types of beetle munch on every variety of tropical tree.
But before you can count species, you have to name them. That’s where the taxonomists come in. The idea of species has been notoriously hard for biologists to define, especially since organisms so often exist on a continuum, becoming harder and harder to distinguish the closer they are to each other. The most widely accepted definition comes from the evolutionary biologist Ernst Mayr, who defined species as groups of animals that breed with one another, but not with others – at least not in the regular course of events. (If you force a zebra and a donkey together to make a zonkey, you’ve created one hybrid, not disproved the fact that they are two different species, since such a mating would not normally occur in nature.)
Taxonomists do not just name individual species; they also have to figure out how species are related to each other. Over the centuries, many scientists have tried to fit the world’s creatures into a coherent system, with mixed results. Aristotle tried to classify all life forms based on their essential traits, and in particular, the way they moved. Sedentary animals gave him the most trouble. He seems to have spent a lot of time on the island of Lesbos, puzzling over whether sea anemones and sponges were animals, plants, or plant-like animals.
The real revolution in taxonomy came in the 18th century, during the age of Enlightenment. It was largely the work of one man, Carl Linnaeus, who was hailed as the Isaac Newton of biology. Linnaeus was an odd figure to rise to such heights: a brilliant, headstrong, egotistical showoff with a prodigious knack for remembering the sexual characteristics of plants. He made one major expedition – to Lapland, in Sweden’s north – but mostly relied on the discoveries of others. He inspired 17 “apostles” to venture into the world in search of specimens to complete his system. Seven never came home. Based on their collective work, he named 7,700 species of plants and 4,400 species of animals.
Later biologists found much to quibble with in Linnaeus’s system. For instance, he grouped hedgehogs and bats together as “ferocious beasts”, and shrews and hippos together as “beasts of burden”. Linnaeus’s lasting achievement was not in creating the groups themselves, but the system by which all subsequent species would be named. He decreed that all species should have a two-part name. The first part indicates the genus to which a species belongs, and the second part is the species name.
This is a brilliantly efficient system for both naming and sorting. With it, we can tell in an instant that we, Homo sapiens, are both related to, and distinct from, our evolutionary relatives Homo erectus and Homo habilis. It is also a source of considerable fun for taxonomists. Presidential names – the bushi, obamai and donaldtrumpi (a remarkably coiffed moth) – reliably grab headlines. Less frequently, species names invoke politics or recent events. A Brazilian mayfly received the species name tragediae, to commemorate the catastrophic collapse of a dam in 2015. Taxonomists are also not above the occasional pun or rhyme. Terry Gosliner, an expert on nudibranchs, or marine sea slugs, once giving the name Kahuna to a species belonging to genus Thurunna from Hawaii, to make Thurunna kahuna.
Gosliner found his first nudibranch while still at high school. Since then he has travelled the world in search of them, and has named more than 300 in his 40-year career. As denizens of coral reefs, sea slugs are particularly sensitive to rising sea temperatures. Some scientists think climate change and ocean acidification might cause reefs to vanish entirely in the next 50 to 100 years. Gosliner tends to be a bit more optimistic, emphasising the reefs’ ability to bounce back from stress. But while corals reefs face peril in the seas, an even greater crisis could be developing for insects on land – the true dimensions of which entomologists are only beginning to grapple with.
Before entomologists could ponder the terrifying possibility of an insect mass extinction, they first had to come to grips with the true scale of insect diversity. They are still struggling to do that now. But for many, the breakthrough moment came in 1982, with a brief paper published by a young beetle specialist named Terry Erwin.
Erwin wanted to figure out how many species of insect lived on an average acre of rainforest in Panama, where he was working. To do this, he covered a single tree in sheeting and “fogged” it, by blasting it with insecticide from a device resembling a leafblower. He waited several hours while dead bugs cascaded on to the plastic sheeting he had spread on the ground. He then spent months counting and sorting them all. What Erwin found was startling: 1,200 species lived on this one tree. More than 100 lived on this particular tree and nowhere else. Scaling this result up, Erwin estimated that there are 41,000 different species in every hectare of rainforest, and 30m species worldwide.
This estimate quickly became famous, and controversial. Erwin is widely respected in the field. He has been commemorated in the names of 47 species, two genera, one subfamily and one subspecies – a good gauge of respect in the entomological community, where, according to the International Commission on Zoological Nomenclature, naming a species after yourself is forbidden by custom, but not law. Still, many entomologists are sceptical about Erwin’s wilder estimates, and more recent studies have tended to revise the 30m number down somewhat. But Erwin remains intransigent. “It’s like Wyatt Earp and Billy the Kid, these kids out here taking potshots at me. None of them have any data,” he told me recently. “They’re just sitting in that office throwing numbers around.” He thinks the real number might be as high as 80m, or even 200m – and that a large number of these species are in the process of vanishing without anyone being around to even notice.
Everywhere, invertebrates are threatened by climate change, competition from invasive species and habitat loss. Insect abundance seems to be declining precipitously, even in places where their habitats have not suffered notable new losses. A troubling new report from Germany has shown a 75% plunge in insect populations since 1989, suggesting that they may be even more imperilled than any previous studies suggested.
Entomologists across the world have watched this decline with growing concern. When Brian Fisher, an entomologist at the California Academy of Sciences with a particular expertise in ants, arrived in Madagascar in 1993, he expected he would be able to describe some new species, but he had no idea of the extent of the riches he would find there. “Everything was new. It was like it was in the 1930s,” Fisher said. In that time, he has identified more than 1,000 new species of ant, including some whose adults feed exclusively on the blood of their own young, a group he has nicknamed the “Dracula ants”.
A thousand ants is quite a lot, but scientists have identified 16,000 species – so far. To a layperson like me, they all seem basically alike. Some are brown, some are black, some are cinnamon-coloured, but other than that, they look pretty much like the (invasive, Argentine) ants that swarm my kitchen in California every time it rains. To an expert like Fisher though, they are as different from one another as warblers are to a birder. Under a microscope, each ant positively bristles with identifying features in their flagellate hairs, their segmented antennae, and most of all, in their mandibles, which under magnification look like diabolical garden shears.
In the decades since Fisher started making expeditions to Madagascar, deforestation has accelerated, and today only 10% of its virgin forests remain intact. Fisher says that “in 50 years I can’t imagine any forest left in Madagascar”. According to Wendy Moore, a professor of entomology at the University of Arizona, who specialises in ant nest beetles, “There is a sense of running out of time. Everyone in the field who is paying attention feels that.” Because many insects depend on a single plant species for their survival, the devastation caused by deforestation is almost unimaginably huge. “Once a certain type of forest vanishes, thousands, or tens of thousands, or hundreds of thousands of species will vanish,” Erwin told me. “Deforestation is taking out untold millions of species.”
While we still don’t have a clear idea of what’s happening to insects at the species level, we are in the midst of a crisis at the population level. Put simply, even if many kinds of insects are holding on, their overall numbers are falling drastically. The alarming new data from Germany, which was based on tracking the number of flying insects captured at a number of sites over 35 years, is one warning sign among many. According to estimates made by Claire Régnier of the French Natural History Museum in Paris, in the past four centuries, as many of 130,000 species of known invertebrates may have already disappeared.
Various kinds of anecdotal evidence appear to support these observations. The environmental journalist Michael McCarthy has noted the seeming disappearance of the windscreen phenomenon. Once, he writes, “any long automobile journey,” especially one undertaken in summer, “would result in a car windscreen that was insect-spattered”. In recent years this phenomenon seems to have vanished.
Although insecticides have been blamed for the declines in Europe, Erwin thinks the ultimate culprit is climate change. The location he has been observing in Ecuador is pristine, virgin rainforest. “There’s no insecticides, nothing at all,” he said. But gradually, almost imperceptibly, in the time he has been there, something has changed in the balance of the forest. Studying the data, Erwin and his collaborators have found that over the past 35 years, the Amazon rainforest has been slowly dying out. And if the forest goes, Erwin tells me, “everything that lives in it will be affected”.
If this trend were to continue indefinitely, the consequences would be devastating. Insects have been on Earth 1,000 times longer than humans have. In many ways, they created the world we live in. They helped call the universe of flowering plants into being. They are to terrestrial food chains what plankton is to oceanic ones. Without insects and other land-based arthropods, EO Wilson, the renowned Harvard entomologist, and inventor of sociobiology, estimates that humanity would last all of a few months. After that, most of the amphibians, reptiles, birds and mammals would go, along with the flowering plants. The planet would become an immense compost heap, covered in shoals of carcasses and dead trees that refused to rot. Briefly, fungi would bloom in untold numbers. Then, they too would die off. The Earth would revert to what it was like in the Silurian period, 440m years ago, when life was just beginning to colonise the soil – a spongy, silent place, filled with mosses and liverworts, waiting for the first shrimp brave enough to try its luck on land.
Conserving individual insect species piecemeal, as is done with most endangered mammals, is extremely difficult. Not only are the numbers mind-boggling, but insects and other invertebrates don’t tend to have the same cachet. Polar bears and humpback whales are one thing; soft-bodied plant beetles from the Gaoligong mountains of Yunnan are quite another.
Not long ago, I took a trip to the first wildlife refuge established with the express purpose of protecting an endangered insect, the Antioch Dunes National Wildlife Refuge, about an hour’s drive north-east of Berkeley, California. The reserve is small – only 55 acres, hemmed in on three sides by a chain-link fence, and by the San Joaquin river on the fourth – and, in truth, the Dunes do not dazzle the eye. The terrain resembles an unlovely, overgrown plot of land intended for development at some unspecified point in the future. The day I went, three vultures huddled around the body of a cat while the turbines of a wind farm spun lazily on the opposite bank of the river.
Once, however, these dunes were a miniature Sahara, home to a number of animals and plants that existed nowhere else. It took decades before that fact became apparent to biologists, and by then, it was very nearly too late. When white settlers arrived in California, the dunes were seen simply as a source of raw materials. The dune sand was unusually well-suited for brickmaking, and between the San Francisco earthquake of 1906 and the postwar housing boom, most of the sand was mined out and turned into buildings. Once the dunes were gone, most of the land they formerly stood on was built up.
It wasn’t until the 1960s that biologists began to realise how special the Antioch Dunes were. By that point, only three native species remained. There were two plants – the Contra Costa wallflower and the Antioch Dunes evening primrose – and one insect, the Lange’s metalmark butterfly. The metalmark butterfly is tiny, with a wingspan about the size of thumbnail. A pretty brown-and-orange with white spotting, they are weak flyers, capable of travelling a maximum 400 metres (1,300ft) after they emerge from their chrysalises for seven to nine days every August.
After the Dunes Reserve was established in 1980, the butterfly enjoyed a brief resurgence. Today, it is struggling. At last count, there were only 67 individuals in the park. The Lange’s lay their eggs on one plant and one plant only: the naked-stemmed buckwheat, which is currently being choked out by weeds. The only other population of Lange’s is kept in a captive-breeding programme at Moorpark College in Simi Valley, California. If something should happen to these, it would be the end of the species.
In a bid to save the butterfly, the US Fish and Wildlife Service has recently begun a bold experiment in habitat restoration, covering much of the refuge in sand. Spread a metre deep, the sand suffocates invasive plants, allowing the species that originally evolved on the dunes to reclaim their lost ground. “If we can bring back the environment, we can bring back the butterfly,” wildlife refuge manager Don Brubaker told me. The day I visited, his co-worker, refuge specialist Louis Terrazas, spotted a hopeful sign. The season’s first shoots of native primrose had just started peeking out above the sand. Given time, this remnant of a remnant might spring back to life.
When I asked Brubaker if his painstaking efforts on behalf of the Lange’s was worth all the trouble, he replied: “Why protect the species? Why not? Because it’s what we do – we’re enabling the planet to keep functioning.”
In some ways, the tiny ranges of invertebrates like the Lange’s Metalmark Butterfly make them perfect targets for protection. Sarina Jepsen is the director of endangered species and aquatic conservation at the Xerces Society, a Portland, Oregon-based non-profit focusing on invertebrates. She told me that for insects, “often small patches of land can make a huge difference,” unlike what is needed for, say, wolf or tiger conservation. “We don’t necessarily need hundreds of thousands of acres to make a difference with these species,” she said. Even so, the amount of work that goes into saving even a single species can sometimes feel overwhelming. It isn’t enough to save one in a lab. You have to rescue whole environments – the products of complex interactions between plants, animals, soil and climate that have built up over millennia.
At a certain point, it becomes clear that to even think about extinction in terms of individual species is to commit an error of scale. If entomologists’ most dire predictions come true, the number of species that will go extinct in the coming century will be in the millions, if not the tens of millions. Saving them one at a time is like trying to stop a tsunami with a couple of sandbags.
Like many of the species they study, taxonomists are presently at risk of becoming a dying breed. Faculty hires, museum posts and government grants are all declining. Fewer students are drawn to the field as well. All too often, taxonomy gets dismissed as old-fashioned and intellectually undemanding, the scientific equivalent of stamp collecting. Molecular biology, with its concern for DNA, proteins and chemical processes within individual cells, dominates curriculums and hoovers up grant money. “All the university courses are oriented towards it, and so is the funding,” says Terry Erwin.
Meanwhile, the new species keep piling up. Already today, as I’m writing, ZooKeys and Zootaxa, two of the largest and most prolific taxonomic journals, have announced the discovery of a potter wasp from South America, a water scavenger beetle from the Tibetan plateau, an erebid moth, an Andean scarab beetle, two Korean crustaceans and a whole genus of parasitoid wasps (don’t worry, we’re safe – the bastards prey on aphids), and it isn’t even noon yet.
What to do with this onrush? Many taxonomists I spoke to admit that it simply isn’t manageable. Brian Fisher confessed that many taxonomists find themselves awed at some point by “the immensity of what we don’t know”. Kipling Will, of the University of California, Berkeley, who has spent two decades studying one subfamily of ground beetles, told me, while gesturing at boxes of samples that had just flown in from Australia: “We do what we can. I have so much undescribed material. It takes decades just to get where we are.” With any species, it takes time to do a proper dissection, test their DNA, compare them to their nearest relatives, and compile all the information necessary to publish something as new. With so many invertebrates being found each year, it’s common for them to spend years, or even decades, in a queue waiting for their coming-out party.
So what to do? And why bother? There are plenty of practical reasons to worry about the fate of invertebrates. They are a vital part of the ecosystems that function as the heart, lungs and digestive system of our planet. Some might carry, inside their exotic biochemistries, cures for any number of diseases. Recently, chemicals harvested from sea slugs have been tested in clinical trials in the US for use as cancer-fighting drugs. Others could be used as natural alternatives to pesticides. But ultimately, it’s not certain that any of these will be enough on its own. The answer could have more to do with aesthetics, or enthusiasm for the living world – the quality EO Wilson named “biophilia”.
When you ask people who work in invertebrate taxonomy why they have devoted their lives to a particular type of insect, snail or clam, the word you hear most often is “beautiful”. Their eyes light up in front of their chosen genus or subclass. The occupants of a case full of slightly iridescent, mostly black beetles will be described as “rather huge and incredibly beautiful”. (Huge is relative, too – they are the size of the final joint of a little finger.) Surrounded by jars full of tiny sea slugs, they will gush about their beauty and the glorious variety of their colour, shape and behaviour. Amy Berkov, a professor of tropical ecology at the City College of New York who works on wood-boring beetles, came to entomology from a background in art and chose her new field, in part, because “there’s nothing more amazing than looking at insects”. Even the ant specialists – generally a pretty hard-nosed-bunch – will trade Latin names of rare ants with the affection you usually hear reserved for old friends.
It’s easy to care about the cute and cuddlies. Soon we’ll be living on a planet that has lost its last mountain gorilla, its last leatherback turtle. A world without tigers or polar bears; what a sad place that will be.
But to think about the coming invertebrate extinctions is to confront a different dimension of loss. So much will vanish before we even knew it was there, before we had even begun to understand it. Species aren’t just names, or points on an evolutionary tree, or abstract sequences of DNA. They encode countless millennia of complex interactions between plant and animal, soil and air. Each species carries with it behaviours we have only begun to witness, chemical tricks honed over a million generations, whole worlds of mimicry and violence, maternal care and carnal exuberance. To know that all this will disappear is like watching a library burn without being able to pick up a single book. Our role in this destruction is a kind of vandalism, against their history, and ours as well.
Take Strumigenys reliquia, one of the ants I heard discussed with such warmth at the California Academy of Sciences. Strumigenys is a predator, a native of the undergrowth, and very rare. It was first discovered in 1986 by Phil Ward of the University of California, Davis. He spotted this incredibly rare species on a two-hectare patch of woods a few miles from his office. It has never been seen anywhere else. Ward thinks there is a reason for this. California rivers were once flanked by giant forests of hardy, flood-resistant, evergreen oaks. Geologists think these riverine forests were a feature of the landscape for at least 20m years. Accounts from early settlers and explorers give an idea of what they might have been like. They write of flocks of geese “blackening the sky”, salmon choking the streams and grizzly bears gathering under the oaks to feed on acorns in troupes of a hundred or more.
Today, except for a few scattered acres like the one Ward found in Yolo County, those forests are gone. They were chopped down long ago for firewood and ploughed under to make way for tomato farms and almond orchards. The salmon, the geese and the grizzlies have all gone too. Only the ant remains. Only it remembers.
Main image: Alamy; Getty; Guardian Design; Sara Ramsbottom
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