Janzen’s wife, Winnie, wandered out from the back room to see what was going on. She had their pet porcupine, Espinita, on her shoulder, and it raised its quills in fear. “You’ve been learning too much from your cats,” Winnie said to Brooks, “bringing gifts to people’s doors.”
It takes a strong friendship to flop a bloody fox on someone’s floor, and Janzen and Brooks have shared exactly that kind of friendship since 1994. (Janzen even named a species of parasitic wasp that he discovered after Brooks.) They met as Janzen was looking for help to count every species in the reserve. No one had ever done something on this vast scale—Janzen estimates that there are 235,000 species in Guanacaste. But he dreamed of having a full inventory of species, which scientists could use as a sort of yellow pages to let them pick out species to study and to help them discover how biodiversity is created and maintained in tropical forests. As soon as Brooks heard of the project, he wanted in.
Brooks has been a parasitologist since the mid-1970s. It was he who figured out how to use the relationships of parasites to reconstruct the wanderings of their hosts millions of years ago. He began working with frogs in Kansas but spent most of his career working in Latin America, looking at the parasites of stingrays, alligators, and other animals. It is slow work, and usually a parasitologist can hope to discover only a sliver of parasite diversity. And that’s why Brooks jumped at Janzen’s idea. “As soon as I heard about what was going on here,” says Brooks, “I turned over all my stingray stuff to my Ph.D. students. I realized this was the place I wanted to make the focus of my work.” For once, in one place, parasitologists might be able to know all the parasites. Guanacaste would become, as Brooks says, “a known parasite universe.”
Janzen was a little puzzled by Brooks when they first met, and I could see some of that bafflement in his face when Brooks laid the fox on his floor. How can someone get so thrilled by a corpse? But Brooks evangelized Janzen until he began to see the parasitic light. “This guy shows up, and my vision of a mouse is changed forever,” Janzen told me. “Now I see it as a bag of tapeworms and nematodes. You have this happy mouse and you open him up and he’s full of them.”
After showing off our find, Brooks and I took the fox to his shed. Brooks switched on the fluorescent light, and moths swarmed in through the chicken wire. He laid the fox down in the freezer, alongside an ocelot and a tapir—other lucky finds that he was going to open up eventually.
We got our drink—Cuba Libre in a can—and when we were done, at about eleven, we drove back to the reserve. Brooks pulled up by the shed and switched the light back on. The best way to see parasites is to open up a fresh body. As a corpse decomposes, the parasites lose their bearings and drift away from their natural homes. Soon they start to die themselves, their bodies disintegrating. So Brooks pulled the fox out of the freezer and got out a pair of scissors.
The fox’s inner ecology turned out to be pretty simple: it was loaded with hookworms, which had been gouging blood out of its bowels. “This guy had a screaming hookworm infection,” Brooks said, pulling apart the fox’s intestine under a microscope. What struck me most about the dissection was Brooks himself. He kept apologizing to the fox as he cut it open—“Sorry, sorry”—kept cursing its stupid death, kept complaining about how the collision had smashed its lungs. The other scientists who worked at Guanacaste looked on Brooks as something of a vampire, a scientist interested in the beautiful animals of the forest only if he could slit them open. But I had never seen someone mourn a dead animal so deeply.
Janzen’s dream of a full inventory fell apart in 1996 during negotiations with the Costa Rican government. Janzen didn’t like how the money for the project was going to be diverted from the central mission of counting species, so he decided he had to abandon it. “We shot the horse in the head,” was how he put it to me. But Brooks was able to get enough money from the Canadian government to keep going with the parasites. He estimates that the nine hundred forty vertebrates of the reserve harbor eleven thousand parasite species (including only the parasitic animals and protozoa), most of which will be new to science. “It’s going to take the rest of my career to do this inventory,” Brooks said. I wondered why he was planning to put himself through so much pain.
Over the course of the next day, I put the question to him a few times and got a new answer each time. Biodiversity is a staggering thing in a tropical forest such as Guanacaste, but you can’t see most of it without the aid of a scalpel. “There are undoubtedly more species of parasites than free-living organisms,” says Brooks. “When you preserve a species of deer, you’re preserving twenty species of parasites from four kingdoms.”
If that’s not enough, you can justify the project out of enlightened selfishness. Most medicines trace their genealogy to some natural compound in some organism, be it penicillin from a fungus or digitalis from foxglove. Only in the past few years have scientists begun to work their way through the parasite’s pharmocopeia. Cordyceps, a fungus that invades insects and sprouts flowerlike stalks out of its body, is the source of cyclosporin, an important antibiotic. Hookworms produce molecules that clasp perfectly with clotting factors in human blood, and biotechnology companies are putting them through trials as blood thinners for surgery. Ticks can also tamper with our blood to make their drinking easier, using chemicals that not only dissolve clots but reduce inflammation and kill bacteria that try to enter a wound. There are other parasitic tricks that still await an explanation. Blood flukes can steal substances out of our own blood to camouflage themselves from the immune system, but no one has figured out how they do it. If scientists did, they might be able to apply their discovery to transplanted organs. A doctor might be able to pump a patient’s blood through a donor lung and essentially turn it into a gigantic protected fluke. That could spare patients from the dangers of immune-suppressing drugs. And these are only a few parasites; who knows what sorts of chemicals the millions of others have evolved?
Another reason for a parasite inventory came up when Brooks and I took a day off from dissections. We drove up the side of Volcan Cacao, thrashing in the back of a Land Cruiser on a road made from boulders. Much of the forest up the sides of the mountain had been cut down by ranchers, but conservationists had bought the land back and were waiting for the forests to grow back down the slopes. We stopped driving at the border of the forest and hiked in, instantly dunked in an ocean of trees, blue morpho butterflies bounding through the shade like fish swimming overhead. A thin rain worked its way down through the thick canopy as we walked over a creek. Brooks stopped to look upstream and down. “This place should be packed with frogs,” he said. And there was nothing.
Beginning in the late 1980s, frogs began to disappear from the high elevations of Central America. On Cacao, not a single species of frog can be found. At first biologists had no idea what was causing the deaths; all they knew was that the corpses of frogs were piling up, untouched by birds. Only in 1999 did a biologist isolate what is probably the cause: a fungus brought down from the United States. Its spores travel through water until they meet the skin of a frog. Thereupon they dig into the animal and devour the keratin in its skin, releasing a toxin that quickly kills it. The only thing that keeps the fungus from killing every frog in Central America is the fact that it’s adapted for cool climates, and it’s too hot for the fungus to survive below a thousand meters.