It’s sunset on an unnamed mountain, in an unexplored corner of one of the greenest countries on earth. We’ve arrived by helicopter across a rumpled landscape of swamps and hills, and it feels as if we’re the first humans ever to pass the night here.

Now five of us sit on a remote ridge of Suri­name’s Grensgebergte Mountains, watching the mist settle over forested hills beyond forested hills, along the border with Brazil. A pair of macaws fly below us, showing off their brilliant colors. A hummingbird whips past, hovers briefly to sip nectar from a costus flower, and vanishes again into the dusk.

“What the hell was that?” cries Brian O’Shea, an ornithologist from the North Carolina Museum of Natural Sciences. “That’s not a great-billed hermit. That’s something totally different.” His head swivels toward a fellow birder. “Did you see how long the tail was? We have to investigate that.”

Somewhere out along the ridge, a flock of marbled wood quail call like a cuckoo clock striking the hour. The scrim of daytime sky gives way to a bright spangle of stars. The birders go off in search of other bird songs, and the herpetologists head out to chase frogs into the night.

Back at base camp a few days later, Piotr Naskrecki, an entomologist from Harvard’s Museum of Comparative Zoology, remains incredulous. “A new hummingbird? Impossible. I mean, it would be fantastic. It would make this trip.” He hesitates just long enough for his competitive instincts to kick in. “Well, not really. I have better stuff.” Then he heads off to catch a flight to the mountaintop.

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We’ve come here, across roughly 240 miles of uninterrupted forest from Suriname’s populated coast, to discover new species and, in my case, to take a firsthand look at what species discovery is all about. Our expedition is set to last just three weeks, closer to a modern bioblitz than a 19th-century voyage of discovery, but with a fair share of the latter’s potential for disease, discomfort and frustration, leavened intermittently by the chance to see something no one has ever seen before. Our group includes 18 scientists, among them ornithologists, botanists, entomologists, mammalogists, fish squeezers and snake grabbers. We also depend on a cadre of local boatmen, builders and cooks to set up camp and negotiate the unpredictable Palumeu River.

The expedition is the result of 15 months of planning, two reconnaissance overflights and $300,000 in expenses, part of a long-term Conservation International effort to identify and protect biodiversity worldwide. It is one of many such projects that are helping make this a new age of species discovery. About 18,000 new species get described in scientific journals each year, according to the International Institute for Species Exploration. This ongoing search for life on earth is not nearly so highly publicized as the search for life in outer space. Many of the species being discovered would cause a global sensation if only they had the sense to turn up on another planet. Finds from the past several years include, for instance, a North African spider that cartwheels its way out of danger and a pancake batfish from Louisiana that hops on its fins.

A point of order about the meaning of discovery: Even a crocodile that has existed only as a fossil for the past 130 million years can suddenly become a “new species.” In fact, most of the new species named each year are specimens from existing museum collections that have been described for the first time in print, with a genus and species name, following the rules of scientific classification. So far, humans have identified about 2 million species; estimates put the total number out there anywhere from 10 million to 100 million. The process is painfully slow: A taxonomist knowledgeable in a particular group has to examine a promising specimen in microscopic detail and compare it with related specimens preserved in natural history museums around the world. If a species proves to be unique, the taxonomist designates a representative sample, or “type specimen,” at a scientific institution.

This process may seem like a colonialist enterprise, a way for Western scientists to take over the flora and fauna of less developed nations. But the same basic urge occurs in almost all human groups. It’s called “folk taxonomy” when barefoot farmers do it. In India’s Western Ghats, for instance, locals recognize three separate species of the genus Biophytum, a leafy little plant in the wood sorrel family, where the scientists long noted only one. The nuances matter to the farmers because they use one for treating scorpion stings, another for earaches and a third as bait. In 2008, genetic analysis showed that the folk taxonomy was right, leading to the description of several species, which thus became “new to science.”

The strength of scientific taxonomy is that it puts local knowledge in a global context. Scientific names are a common language, spoken on this expedition by an Amerindian primatologist, a Canadian mammalogist of Chinese extraction, a Surinamese herpetologist from a Hindu family, a Polish entomologist living in America, a Dutch botanist living in Denmark, and a polyglot band of others.

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Our expedition begins in the capital city of Paramaribo, where scientists gather to study maps and overflight photos. The target area includes a couple of inaccessible mountains. That’s promising, because their isolation and elevated topography make them possible havens for new species. But helicopter landing areas appear to be lacking. Andrew Short, an associate professor of ecology and evolutionary biology at the University of Kansas, suggests jumping off while the chopper hovers, then climbing back aboard after a “lightning” raid for specimens. He wants to do this for microscopic water beetles, which are his passion. Someone worries that an overeager explorer might fall off a cliff in pursuit of his quarry. Naskrecki studies the landscape and tries to be reassuring. “You’ll roll off. You won’t plummet.”

An advance team, mainly members of the Wayana and Trio communities along the Palumeu River, has set out ahead in eight boats loaded with 6,600 pounds of equipment. Heavy rains have complicated their route, forcing them to unload the boats below the Kasikasima Rapids and haul each one uphill through the forest. The team must carry the cargo on their backs, reload it onto the boats, and push upstream again—repeating the process over and over. It takes them ten days to reach the destination. Then the team sets to work expanding an agricultural clearing to serve as a helipad.

For those of us arriving in leisurely helicopter relays, that helipad looks like a pinhole cut in the dense, endless forest. Our pilots gently deposit us, and the biologists vanish into terra incognita. Naskrecki almost instantly has his first potential new species. It’s a fungus that has taken over the body of a jumping spider. He notices it only because the spider’s eyes still rise plaintively above the thick mat of parasitic growth. The fruiting bodies on its back look like a tray of cream cupcakes topped with red candy drops. “Or nipples,” says Naskrecki. There’s also a fungal stalk jutting up in front of the spider’s eyes, like a rhino horn.

Suriname is still almost 95 percent forest, and becoming a hotbed for species discovery could make for a powerful nation brand, according to Russell Mittermeier, the executive vice chair of Conservation International, who has visited more than 30 times over the years. “Suriname is the greenest country on earth,” he says one night at base camp. “The whole damned thing is green. We’re trying to demonstrate that developing a green economy based on natural resources is the way to go. You could easily make this competitive with Costa Rica.” The new-species angle, he adds, could be “the piece that says this is something new and exciting. People always connect with that. They connect with the adventure part, too. You’re flying around in remote areas, and sometimes the helicopters don’t work.”

Our own helicopter has just come down to earth with its engine smoking. There are not nearly enough boats to bring us all back to camp. At dinner that night, Naskrecki notes in a tone of purely scientific interest that there are more sand flies than he has ever seen anywhere, and that sand flies transmit leishmaniasis, a dreaded affliction among tropical explorers. Someone else reports having seen an open leishmaniasis sore on one of the boatmen. Then the rain starts rattling down.

We have mosquito nets, tarps and ripstop nylon tents. But the sense of being stranded in the wilderness recalls past explorers who endured far worse in the pursuit of new species—the 19th-century English naturalist Henry Walter Bates, for instance, who went hungry and occasionally barefoot (“a great inconvenience in tropical forests”) during 11 years of collecting on the Amazon. Or his Welsh colleague Alfred Russel Wallace, who endured the fungal smell of clothes that never quite dried (not to mention malaria) during four years in South America—only to lose his collections when his ship burned and sank in the middle of the Atlantic Ocean. And yet where modern readers might expect misery, the journals of these explorers instead delight in discovering new beetles, butterflies and other species.

A replacement helicopter eventually arrives and sets Short down on a bare saddle of the mountaintop. As a kid growing up in Newark, Delaware, Short used to dam up pools in the stream behind his family’s house, and it eventually led him to specialize in aquatic insects. Now he travels to remote elevated regions, finds the places where water seeps down rock faces and gets out an ordinary kitchen dish brush to scrub up the algae and make his water beetles come scrambling out. Here on the mountain, he spends 14 hours and collects what he believes to be a dozen or more new species, and four new genera, all swimming in a plastic vial he refers to as “the awesomeness.”

When he returns later, someone remarks that they look like dirt. Short patiently explains that there’s also dirt mixed in (“otherwise the awesomeness would be blinding”) and that most of the beetles are smaller than pinheads. These are all “beetles no one has ever seen before,” he says. “So everything that’s known about these beetles is in my hand, or in my notebook, or in my mind.”

O’Shea is also back from the mountaintop, but his mood is less luminous. “Stop asking about the f------ hummingbird,” he mutters. He caught his quarry from the costus flower and delicately extricated it from his mist net. But in the sober half-light of the forest, he recognized it as the well-known sooty-capped hermit. Disappointment is the bleak wingman of discovery.

What did Naskrecki find? Up the trail behind base camp, he aimed his headlamp at a leaf, then reached out with the sort of tongs used to grab groceries on a high shelf. It had two strainers attached, and he clapped them together to trap a katydid inside. After studying his catch, Naskrecki said, “Oh, my God.” Most male katydids make their mating song by sweeping their wings together in front of their bodies. One of their wings has a scraper, like a violinist’s bow, and the other has an amplifying box, like the body of the violin. This katydid was a silent male; it had no violin. “The loss of sound production is extremely rare,” he said. “It’s happened in only four species in a family of 10,000. This is the fifth.” He bagged the specimen. “Wow! Incredible.”

For all his delight in such discoveries, Naskrecki takes a grim line on why they matter. “What I see taxonomists doing,” he says, “is putting names on tombstones.” Species are currently disappearing far faster than new ones are being discovered, largely because of habitat destruction, deforestation and climate change. Naskrecki hopes to describe as many as possible before they vanish forever. “I can’t stop extinctions,” he says. “But at least we will know what we have lost.” Species that look identical to human eyes can be dramatically different from one another, says Burton Lim, a small-mammal specialist from the Royal Ontario Museum. Over the past few years, DNA sequencing has allowed humans to peer into these differences for the first time. The largest land mammal on earth, for instance, has turned out to be two separate species of African elephants; the tallest mammal turns out to be four species of giraffes. Once biologists are clued in to these genetic differences, they frequently find that newly identified species behave differently. One bat may prey on a different species of moth than another, for instance, or pollinate a different flower, and it may take both species to keep a habitat healthy.

One common argument for species discovery is that a newly identified plant or animal may one day prove invaluable to humans. For instance, the antiretroviral AZT, which turned AIDS from a deadly global pandemic into a manageable disease, was derived from an obscure Caribbean coral reef sponge discovered in 1949. This utilitarian argument is not, however, what motivates the expedition scientists. They do not expect their new species to provide the cure for cancer or the next biofuel. “Probably 99 percent of species on earth have no direct impact on our affairs,” says Naskrecki. But naturalists are driven to discover them anyway for the same reason space scientists work to discover new planets: “We want to know what’s out there.”

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One day the rains come, and keep coming, till it dawns on us that we have sited our base camp on a flood plain. Short builds a dam to block the rising water, but the Palumeu soon threads channels around us.

“Get out of bed!” a voice cries in the darkness before dawn. “Get out of bed now!” It’s the insistent, sleep-wrecking voice of camp counselors and drill sergeants. We peer over our hammocks, and the river is right there beneath us. Everyone scrambles to pack up specimens, equipment and baggage.

At the helipad, O’Shea and Serano Ramcharan, a Surinamese wildlife specialist, identify bird calls. “White-throated toucan,” says Ramcharan, of a sound like puppies being tortured. O’Shea picks out the wolf whistle of the screaming piha. They go back and forth, rapid-fire. It takes them just ten minutes to get 20 species. As we lift off, the helicopter pilot, also in a musical mood, sings “So Long, Farewell” from The Sound of Music.

At our new camp just above the Kasikasima Rapids, the scientists redeploy their dragnet of seines, mist nets, pit traps, Winkler extractors, aluminum boxes and other collecting devices. Specimens flow into the tent. Many of the researchers carry sophisticated species databases with them on their laptop computers, including photos of type specimens. Thus they can experience the euphoria of a new discovery in the morning and, by mid-afternoon, be crestfallen when the database reveals that somebody else described the same species a century ago. But it’s better to be disappointed quickly and move on to the next thing than to linger for months in false hope.

Lim has what looks to be a new species of mammal, a kind of rice rat with unusually large hind feet, although closer examination back in the lab will reveal that it’s simply a big-footed version of an existing species. But Naskrecki’s katydid will be confirmed as a new species. Short will return home with an estimated 26 new species and 8 new genera (though it will take years for them all to be published with formal names). The expedition, all told, will come back with about 60 species that are new to science. Conservation International will use these discoveries to help inspire Suriname’s National Assembly to preserve 72,000 square kilometers of rainforest. (The Trio and Wayana communities declared this area an indigenous conservation corridor in 2015. Now CI is working with the government to set up legal designation, zoning and financing for the nature preserve.)

Near the end of the trip, we make the long climb in from the river to the mountain called Kasikasima. Massive granite boulders, grooved and mossy from eons of rainfall, remind us that we are traveling across one of the oldest geological formations on earth, the Guiana Shield, largely unchanged in billions of years. We step out of the brush onto a bare plateau, as if stepping onto a stage.

Below us, the shadows of clouds make their way across endless forest, and the sunlight catches on a bend in the Palumeu River. Someone points out the Orange Mountains off to the east. The story among locals is that they are home to “ape men.” Even now, almost anything is possible here on earth. Below us, howler monkeys are roaring. For a moment, it’s as if the most extraordinary planet in the entire universe lies spread out before us, still waiting to be discovered.