Searching for the Rarest of the Rare in the Amazon rainforest

I write this on my way to Tasmania to look for two of my favorite groups of invertebrates, velvet worms (Onychophora) and harvestmen or daddy longlegs (Arachnida, Opiliones). I’ve been studying these two fascinating groups of organisms for the past 25 years. This article is about the study of these obscure animals. I have collected invertebrates all over the world, from the waters of Antarctica, where invertebrate life is splendorous, to the densest tropical rainforests, in all continents, in all oceans. To find the rare is the greatest privilege and the most spectacular adventure, whether for pleasure or research.

Just last week my brother and I went on a safari to photograph a rare cat in southern Spain, the Iberian lynx. The Iberian lynx is one of the rarest cats in the world, once considered more vulnerable than other famous cats like the snow leopard. After being at the brink of extinction, the Iberian lynx has had a considerable comeback, but it still has a long way to go. Seeing this extremely rare and almost mystical animal is hard to describe, and it brings up many hidden emotions.

A year ago, about this same time, my brother was visiting the United States and we traveled to Maine, six hours each way from Boston, to look for another rare animal. A lonely Steller’s sea eagle had been spotted in multiple localities in Massachusetts and Maine that week. This was the first time the species had been seen in this part of North America. This single animal drew hundreds or thousands of people, some flying from places as far as Texas, to have a glimpse at a single bird. The excitement of those who saw it was as patent as the disappointment of those who didn’t—us! I could not resist though, and a week later, after my brother had returned to Spain, I did the trip on my own, and did get to see this beautiful eagle, on a stormy day, far away. The photos were not worth the trip, but seeing the animal was already worth it. Why do we do this? Why do we get so excited to see these rare animals? I believe this is something innate to humans, that clearly impacts us as children, persisting in some of us even when we grow up.

  A, Iberian lynx at sunset, photographed in Ciudad real, Spain; B, Iberian lynx; C, footprint of a jaguar from Reserva Ducke. All photos in this article by Gonzalo Giribet.

I am lucky to get to do something similar for a living, collecting rare invertebrates for Harvard’s Museum of Comparative Zoology for my research on evolution and biogeography—the science that studies why organisms live in particular places. Questions such as why are there no penguins in the North Pole or polar bears in Antarctica have a clear evolutionary response; penguins evolved in the Southern Hemisphere and are not able to cross the warm waters that separate the two hemispheres (note that penguins live in Galapagos because of the cold Humboldt current coming from the south) and bears evolved in the northern continents and only made it to the southern continents after Antarctica had severed its connection to South America and Australia. Evolutionary thinking gives us responses, including to the mother of all questions: what came first, the chicken or the egg? This question is often posed when no possible answer can be provided, by in fact an answer to these questions is clear, if we think in evolutionary terms, as chickens are related to other birds, birds are related to dinosaurs and so on… and all these animals laid eggs, so clearly, the egg came before the chicken!

In the quest for rare invertebrates, I’ve been on many expeditions around our planet, including many in Latin America. One that had a huge impact on me was an expedition to Amazonia in the summer of 2012. The journey was divided in two parts, one to a well-known investigation site and the second on a little-traveled odyssey on the Rio Negro. For the first part, we sampled the best-studied plot in the entire Amazon rainforest, a sector of the forest near Manaus called Reserva Adolpho Ducke, a 6 x 6-mile (10×10 kilometer) plot divided by a grid that has been used for a myriad of ecological and faunistic studies. We probably know more about this 6 x 6-mile plot than about all the rest of the immense Amazon rainforest.

After a week of sampling harvestmen, we had collected a large number of species, about half of them new to science, meaning that no one had seen or named these species before. If a 6 x 6-mile forest plot, near a large city, contained 23 new species in a group like harvestmen, what could we expect when sampling more remote areas of the Amazon or more obscure groups of animals?

Back to our lynx or the snow leopard, these animals are rare because the first one has a relatively narrow distribution, mostly due to habitat destruction and lack of prey, but still thousands of people have had encounters with this elusive cat. The snow leopard is also endangered due to habitat loss, but it is rare because some solitary cats have very large territories. Still, people see these elusive and rare cats. In Reserva Ducke we also saw evidence of a large cat, a jaguar. But what excited us the most were the new species we discovered, two new species of velvet worms (one of which illustrates the cover of a recent textbook on invertebrates I co-authored with Greg Edgecombe), and the many uncharted species of harvestmen (Fig. 2), which had been only spotted by a bunch of scientists. 

For the second part of the trip, funded by the National Geographic Society Explorers program, we embarked on an expedition up the Rio Negro, following the footsteps of one of the greatest explorers of all times, Alfred Russell Wallace. Although most of Wallace’s Amazon specimens were lost when the boat that returned him to England caught fire and sunk, his writings and the mapping of the Rio Negro lasted forever. But Wallace was more famous for his expedition to Southeast Asia and his biogeographic studies there. During that trip, he sent a letter to Charles Darwin telling him about his theory of evolution, which triggered the reading of their joint paper on July 1, 1858 (Wallace was in the Indomalay archipelago at the time) at the Linnean Society of London titled “On the tendency of species to form varieties; and on the perpetuation of varieties and species by natural means of selection.” Wallace is thus considered by modern biologists as the “co-discoverer” of the mechanisms of biological evolution, together with Charles Darwin, even though this is not well known by the general public. Following the footsteps of Wallace in the Rio Negro was not a small feat.

  Animals from Reserva Ducke: A, cover of textbook from Princeton University Press featuring a new species of velvet worm from our Brazil expedition of 2012; B, undescribed species of Macroperipatus; C, the largest spider, Theraphosa blondi; D, an undescribed species of harvestman in the genus Discocyrtus; E, an undescribed sclerosomatid daddy longlegs; F, undescribed cosmetid harvestman; G, another undescribed sclerosomatid daddy longlegs; H, Phareicranaus manauara, one of the many tropical harvestmen that show parental care, guarding clutch of eggs; I, the harvestman Protimesius longipalpis.

The Rio Negro expedition required renting a large river boat that would serve as our home and laboratory for the next two weeks. We settled on a tall white and green beauty named Uape Azu, with a fantastic crew, including Doña Cristina, aka “A feticheira da cozinha,” our talented cook. We did the food shopping for 15 people for the two weeks, and the next morning we started sailing off from Manaus, crossing the white waters of the Amazon river towards the black waters of the Rio Negro. As we slowly cruised the Coca-Cola-colored waters, Doña Cristina realized that we had not done our shopping properly and sent one of the small accessory boats off to a local river community to purchase another 40 pounds of chicken!

We sailed for almost three days towards one of the river’s tributaries, the Rio Jufarí. The reason to go there was to find a tiny harvestman called “? Gen. enigmaticus,”an enigmatic animal not assigned to any particular genus at the time, that had only been collected once, in 1966 by L. Beck, and described in 1969 by German harvestman guru Professor Jochen Martens. No one had ever seen this animal since 1966 and only three specimens were known. Translate this to the vertebrate world, and it would be considered probably among the rarest vertebrate in the world. In fact, most vertebrates are known from multiple locations and multiple specimens, even those which are deemed extremely rare. But the number of invertebrates known from a single collecting event is in the tens or hundreds of thousands. And so many remain to be discovered!

In some groups of invertebrates, people estimate that more than 90% of species remain to be discovered. Certainly, since I started working on the tiny mite harvestmen in 2000 (the group I was after in this expedition), we have doubled the number of known species, basically, a group of recent taxonomists have described as many since 2020 as there had been described since 1802, when the first mite harvestman was described.

A, inundated forest with houses in the water; B, the Uape Azu tide to a tree top; C, the Uape Azu sailing among the tree tops in the inundated forest; D, one of the small support boards taking us to dry land for collecting; E, our laboratory setup on the upper deck of the Uape Azu; F, talking to one of the communities of the Rio Jufarí; G, crossing an igarapé to get to dry land for collecting; H, inundated forest edge.

When we arrived at our destination, we tied the boat to the top of a tree that was 90% underwater, as we were traveling after a very wet rainy season. This is when the term “inundated forest” really hit me. Entire trees underwater, floating houses, other houses, where people lived, were half underwater, the hammocks hanging barely above the water level. Even though I had spent a lot of time in the jungle, I had never seen such a thing. It fascinated me. Our routine consisted of finding accessible dry land with the smaller support boats and have our “mateiro” Osmaildo open a trail with his machete, so we could then find a small area to work, looking under logs or sifting leaf litter to find small creatures living in the forest.

Alternatively, we could set off from the community crossing an igarapé (image 3G) until reaching dry forest. Suffice to say that we found lots of the mite harvestmen that had only been collected five decades earlier and that we were able to properly study this animal back in the laboratory. We discovered lots of new species and recollected others also known from the area by a single specimen, such as a species of Ricinulei, a rare group of arachnids known as “hooded tick spiders” because they have a hood covering their “mouthparts”—but they are neither ticks or spiders. During the expedition we also engaged with the local river communities, who live between two worlds. We lectured the kids in their church, while showing them images of the animals we had come to look for from so far away.

Another memory of this trip is the sky, so clear, reflected on the black waters, which provided a perfect mirror image. I have only seen such sky in the most remote places of the Congo basin or the deserts of Namibia, realizing how much we have grown accustomed to the light contamination that keeps us from seeing the stars. This was a truly wonderful expedition with some of my best colleagues.

A, One of our Brazilian counterparts searching for small creatures in sifter leaf litter; B, a scorpion, Tityus obscurus; B, the mite harvestman Neogovea enigmatica; C, a new species of daddy longleg in the genus Guasinia; E, male Ricinulei, Cryptocells iaci; F, an amblypygid or whipe-spider, Heterophrynus sp.

The trip ended with a big incident at the airport that involved the environmental police getting our entire U.S. team from Harvard and The George Washington University off the plane, missing our flight, and not even compensating us or apologizing for their mistake. We were able to fly back home a day later. But despite the inconvenience, this trip to the Amazonia remains one of the most productive and mystical of my life.