This story appears in the April 2021 issue of National Geographic magazine.
On a balmy January morning in Manaus, a Brazilian port city surrounded by rainforest, a group of entomologists and I scattered into a supermarket to stock up for an expedition.
Twenty minutes later, in the checkout line, it became clear that we had different ideas about what that meant.
I had peanuts, raisins, and bug repellent; the entomologists, all of whom were dipterists, or fly specialists, had heaps of bruised produce, nearly expired trays of chicken, and bits of peacock bass wrapped in cellophane.
“I asked for the worst tomatoes they have, the most rotten potatoes and onions—that’s the kind of stuff flies like,” said Dalton de Souza Amorim, a professor of entomology at the University of São Paulo.
Wearing a T-shirt stamped with a sketch of Plagiocephalus latifrons, a fly with a head shaped like bicycle handlebars, Amorim said dipterists often use putrid food to bait traps on the ground, where the majority of their research is focused. But on this trip, he and his colleagues—Brian Brown, the entomology curator at the Natural History Museum of Los Angeles County; Stephen Marshall, an emeritus professor from the University of Guelph in Ontario; José Albertino Rafael of the National Institute of Amazonian Research (INPA); and two research assistants—had a more novel mission.
We were headed two hours northwest to a 40-meter (131-foot) steel tower that rises from a pristine area of rainforest. Built in 1979, the tower had long been used to track the exchange of carbon dioxide between the atmosphere and the trees. More recently, it also had become the site of a pioneering entomology experiment.
For years, dipterists had suspected that the fly species occupying the Amazon rainforest’s floor differ from those found among its lofty trees, but no one knew how different they were.
After many visits to the tower for other experiments, Rafael got to thinking: What if he used the tower to find out? In 2017 he set five insect traps at various heights of the tower, starting at the ground level and spacing them every eight meters (26 feet), up to 32 meters (105 feet) high. He hoped doing so would reveal new insights into the stratification of insects in the forest.
Two weeks later Rafael returned with Amorim and was pleased to see the traps stuffed with insects. When the pair sent the samples to colleagues for closer examination, their excitement grew. Of the more than 16,000 flies collected in two weeks, there were thousands of species that even experts couldn’t immediately identify.
Insects are to the animal kingdom what the deep sea is to Earth: largely unknown to science. “We think because we know the birds and the mammals that we’ve already discovered what’s on this planet. In fact, we’ve just scratched the surface,” says Brown.
The Smithsonian Institution says that “there are more insect species that have not been described (named by science) than there are insect species that have been previously named.” Flies are particularly diverse: More than 124,000 species have been identified, but scientists suspect countless more are awaiting discovery.
The Amazon is home to at least 10 percent of the world’s known biodiversity and hundreds of thousands of insect species. But it’s an uncertain time for the rainforest and for insects.
A 2019 study suggested that about a third of insect species would be vulnerable to extinction in the next few decades, a result of habitat loss from intensive agriculture, pesticide and fertilizer pollution, and climate change, among other factors. And in Brazil, President Jair Bolsonaro zealously has been promoting development of the Amazon, more than 300,000 square miles of which has been lost to industry since the 1970s.
Although it’s common for scientists to stumble upon new insects in the Amazon, the volume of unfamiliar fly specimens caught in Rafael’s tower traps was staggering. “It was like they discovered a new continent in terms of the level of novelty,” Brown said.
(Brian Brown, curator of entomology at the Natural History Museum of Los Angeles County, photographed all the insects in this article using a camera-and-microscope setup that was originally developed to examine flaws in computer chips.)
Moreover, many species appeared only in traps set above the ground level. “Finding a separate fauna in the canopy was astonishing,” Amorim said later. “Almost two-thirds of fly diversity is present in the eight- to 32-meter traps, but not in the soil. That means quite a lot of loss when big trees are cut down.”
Many of the mystery flies seemed to be phorids, humpbacked creatures the size of a few grains of salt, some of which are parasitoids that jab their eggs into bees, ants, and other insects.
Brown, one of the world’s preeminent experts on the family Phoridae, knew he needed to see these new phorid species in the wild for himself—and as quickly as possible. “I always feel like we’re one farmer and machete away from losing a whole bunch of species,” he said ruefully.
He arranged an expedition with Rafael, Amorim, and Marshall, who had been his professor when he studied entomology at the University of Guelph. Their schedules aligned to meet in Manaus just after the New Year—and just before the coronavirus spread worldwide—in January 2020.
Like children antsy to get to an amusement park, the dipterists squirmed excitedly as Rafael’s truck bumped through the rainforest. When he turned onto the clay track that led to the tower, they could no longer contain themselves.
They burst out of the truck, left idling on the side of the deserted road, and crowded around a bush that buzzed with insects. Within minutes, they were catching critters with their bare hands.
“That’s a ceratopogonid, I think,” Brown said as he hunched over to look at the fly on Rafael’s palm. Heloísa Fernandes Flores, a graduate student who conducts research with Amorim, rushed to collect it while Brown pointed out a tarantula hawk, a large wasp that preys on tarantulas and has one of the most painful stings in the animal kingdom. The dipterists were delighted to spot one; I was delighted it stayed a respectable distance from my face.
The next morning the scientists began working in earnest. Dressed in khaki hiking pants tucked into rubber boots, Brown started most mornings by climbing to the tower’s eight-meter (26-foot) level. There, he would remove a sizable bottle of diluted honey from his messenger bag and squirt it onto the leaves to lure bees and, by extension, the phorid flies that attack them, using sharp ovipositors to ram eggs into their bodies. He would repeat the same thing at 16 and 24 meters (52 and 79 feet), to see whether different flies showed up at higher elevations.
The swarms of petite stingless bees that arrived to feed on the honey proved irresistible to Melaloncha, or bee-killing phorid flies, which alighted on the leaves next to them.
“The flies curl their abdomen underneath their body, so the sharp part to attack the bees is right up under their head,” Brown narrated one morning, watching a phorid chase down a bee through the viewfinder of his camera. “Then it gets in the right position and uses its ovipositor to jab an egg in between the hard parts of the bee.”
When he was satisfied with his recordings, Brown would collect a few specimens with his aspirator, a long rubber tube attached to a rigid hollow tip, with mesh between them. He would put the rubber end in his mouth, scan the leaves for phorids, and point the rigid end at the flies he wanted to trap.
“You have to suck hard and be decisive,” he said. “There’s one.” He pointed the tube at a barely visible speck and inhaled it into captivity.
Despite the oppressive humidity, Brown did not waste a second in the rainforest. When he wasn’t collecting specimens or recording videos, he was scrutinizing his finds under a microscope or chatting with his fellow scientists about flies. He and Marshall, his former professor, spoke of other dipterists as if they were star athletes—referring to them by their last names only.
On one of our final mornings in the rainforest, we woke groggily after a night’s sleep that had been interrupted by the incessant barking of the station’s adorable, but loud, red mutts.
“I think they killed a possum,” Amorim said, yawning.
Without missing a beat, Brown asked brightly: “Does it have any bees on it?”
Brown’s passion for flies is profound, but he recognizes that others might need convincing. One morning at the station, Brown and I talked about the importance of his work and the challenge of conveying it to others.
When he makes presentations to the public, Brown likes to explain that flies are nature’s great recyclers. Fly larvae consume food waste, fallen leaves, dead animals, and feces, and they turn it all into nutrients that can be used by other creatures. Fruit flies, which share about 60 percent of their genes with humans, are crucial to genetics research. “And if people are totally cynical,” he says, “I tell them flies pollinate cacao. Without flies, you wouldn’t have chocolate.”
Though life without Lindt sounded gloomy enough, I asked what else might happen if fly populations were to disappear.
As he focused the lens of a microscope to examine a new phorid species, he asked, Have you heard of the parable of the rivet popper by Paul and Anne Ehrlich?
“Imagine you’re on an airplane and you see someone popping rivets off the wing. So you talk to the guy, and he says, ‘Oh well, we probably don’t need all of these rivets. They’re all doing more or less the same thing, and if we get rid of a few of them, it’s not going to make any difference.’ ”
I told him that sounded frightening.
“That’s the way that species are in ecosystems. People who don’t care say, ‘We’re not going to miss a few phorid flies.’ But at some point, we’re going to get to where ecosystems aren’t sustainable anymore.”
Brown paused, letting the squawks, chirps, and croaks of the rainforest fill the air. Then he sighed, stood up, and began gathering his gear to head to the tower.
This is writer Haley Cohen Gilliland’s first story for the magazine. Photographer Craig Cutler specializes in still life and environmental portraiture. Entomologist Brian Brown uses macrophotography to study insects.