Parasite Rex: Inside the Bizarre World of Nature's Most Dangerous Creatures

Epilogue

While I was writing Parasite Rex I went on a string of blind dates. A friend of mine had decided to become my matchmaker, having heard the bit of Jewish lore that three successful matches gives you automatic entry into heaven. The fact that my friend was a Chinese Muslim did not diminish her zeal. Unfortunately, by the time she was done with me, she was no closer to a home in the clouds. The dates fizzled for all the various reasons that dates fizzle. However, one in particular still sticks in my memory today, over a decade later. I was sitting with a woman in a restaurant terrace on a warm night in Greenwich Village. Surrounded by paper lanterns, we were discussing what we did for a living. She told me about advertising. I said I was writing an entire book about how amazing parasites are. She tried to change the subject of the conversation. It was as if I had stuck a thorn in the evening’s bicycle tire. I could almost hear the gentle hiss as it slowly and steadily went flat.

As I described the book on that ill-fated night, I realized what a strange, isolated world I had entered. I regularly drew out life cycles of parasites, marking up paper napkins with arrows traveling from snails to ants to birds. I knew which species of blood fluke infects the blood vessels behind your intestines and which one dwells behind your bladder. I thought that Louis Pasteur should move over and make room in the history of science for Friedrich Kuchenmeister, the tapeworm pioneer, even though I suspected that I was the only person in my time zone who even knew who Kuchenmeister was.

Fortunately, by the time Parasite Rex was published in 2000 I was happily engaged to my wife, Grace, who was not scared off by my obsession. And once people had a chance to read the book, I discovered many kindred spirits. A radio producer asked me to appear on her show, saying that I had given her nightmares for a week. She meant it as a compliment. At a party at the New York Public Library, a high school librarian introduced herself to me. She told me that Parasite Rex had been stolen six times from her library, setting a record. I took that as a compliment as well. The very least I could do, the librarian told me, was to talk to her students. A few weeks later I arrived at her school, carrying a carousel filled with the goriest selection of slides I could find.

Sometimes when I traveled to talk about parasites I would meet people who had their own stories to tell me. On a visit to Johns Hopkins in 2006 a malaria expert told me about a strange sight he saw one day in Zambia. As he walked down a road, he saw a wasp and a cockroach in front of him. When he came up close to them, it looked as if the wasp was leading the cockroach by pulling an antenna, like a dog on a leash.

I suspected he was outside his malarial zone of expertise, but he assured me that a scientist in Israel studied the wasps and was figuring out how they turn cockroaches into hosts for their offspring. So I contacted the scientist, one Frederic Libersat at Ben Gurion University. It turned out that the wasps were real. And they were stranger than I could imagine.

The wasps are beautifully named in both Latin and English: Ampulex compressa, aka the jewel wasp. When a female Ampulex is ready to lay her eggs, she seeks out a cockroach. Landing on the prospective host, she delivers two precise stings. The first she delivers to the roach’s midsection, causing its front legs to buckle. The brief paralysis caused by the first sting gives the wasp the luxury of time to deliver a more precise sting to the head.

The wasp slips her stinger through the roach’s exoskeleton and directly into its brain. She continues to snake her stinger—a bit like a surgeon snaking his way to an appendix with a laparoscope—until she reaches the particular knot of neurons that produces the signals that prepare a cockroach to start walking. The wasp injects a second venom that quiets those neurons down so that the cockroach cannot make itself move.

From the outside, the effect is surreal. The wasp does not paralyze the cockroach. If the cockroach is spooked, it will jump, but it will not run away. The wasp then takes hold of one of the roach’s antennae and leads it, like a dog on a leash, to its doom: the wasp’s burrow. The roach creeps obediently inside and sits there quietly as the wasp lays her egg on its underside. The wasp then leaves, sealing the burrow and entombing the still-living cockroach.

The egg hatches, and the larva chews a hole in the side of the roach. In it goes. The larva grows inside the roach, devouring the organs of its host, for about eight days. It is then ready to weave itself a cocoon, which it makes within the roach as well. After four more weeks, the wasp grows to an adult. It breaks out of its cocoon, and then out of the roach.

The sting is what fascinates scientists like Libersat most. Ampulex does not want to kill cockroaches. It doesn’t even want to paralyze them the way spiders and snakes do, since it is too small to drag a big paralyzed roach into its burrow. Instead, it just delicately retools the roach’s neural network to take away its motivation. Its venom does more than make roaches zombies. It also alters their metabolism so that their intake of oxygen drops by a third. The Israeli researchers found that they could also drop oxygen consumption in cockroaches by injecting paralyzing drugs or by removing the neurons that the wasps disable with their sting. But they can manage only a crude imitation of the wasp’s venom; the manipulated cockroaches quickly dehydrated and were dead within six days.

The wasp venom somehow puts the roaches into suspended animation while keeping them in good health, even as a wasp larva is devouring it from the inside. Scientists don’t yet understand how Ampulex manages either of these feats. Part of the reason for their ignorance is the fact that scientists still have much to learn about nervous systems and metabolisms. But millions of years of natural selection has allowed Ampulex to reverse engineer its host. We would do well to follow its lead and gain the wisdom of parasites.

I could not believe at first that I could have written an entire book on parasites and miss a marvel like the jewel wasp. But as the years pass, I continue to learn of more parasites, each of which that brings back that old familiar feeling of spooky respect. There are simply too many parasites for anyone to appreciate them in full. And the catalog of parasites grows each year, as scientists discover new ones. In 2009, I discovered that one of those parasites had been named after me.

The news came from a young parasitologist named Carrie Fyler. In college, Fyler was not sure what to do with her life. She was captivated by parasites but couldn’t believe that a life could be made out of that passion. Then she read Parasite Rex and changed her mind. She went to graduate school at the University of Connecticut to study with the parasitologist Janine Caira. Caira’s specialty is the study of tapeworms that live in sharks and their relatives. Fyler has traveled with Caira to places like Senegal and Chile in order to dissect fish and pluck out their tapeworms. Fyler wrote her dissertation about a genus of tapeworms called Acanthrobothrium, which includes 165 known species. As part of her research, she examined some mysterious Acanthrobothrium tapeworms that Caira and her colleagues had discovered on a 1999 voyage aboard the Ocean Harvest, a commercial trawling ship sailing the Arafura Sea off the north coast of Australia. The fisherman pulled up a massive whip ray belonging to a species never seen before. Caira was more interested in its tapeworms, which were equally new to science.

There are about 1.8 million species of animals, plants, fungi, and microbes that have names. There are many millions more still to be named. Each year, scientists name tens of thousands of new species, which means that they have centuries to go before they finish the job. We name our children as soon as they’re born, but naming a new species comes long after its discovery. Once scientists find an organism that looks like it just might not belong to any known species, they search the scientific literature to see if it is indeed new to science. If it is, they inspect it in painstaking detail, observing all the information one might be able to use to identify another organism as belonging to the same species. This is not the sort of work a genesequencing robot can do for you on your lunch break. This is natural history, old school.

There are some 6,000 species of tapeworms named so far, but scientists regularly discover new ones. When Fyler examined the whip ray tapeworms Caira gave her, she discovered that they were five new species. As she began to describe them, she decided to name one of them Acanthobothrium zimmeri.

I’m happy to report that A. zimmeri is a fine parasite. It has the bizarre anatomy that you’d expect from a tapeworm—an animal that has abandoned brains, eyes, and mouth and has turned its skin into inside-out intestines. Its head is festooned with a distinctive set of suckers, hooks, and muscular pads, which presumably it uses to clamp onto the gut of its host. Like other tapeworms, the rest of its tiny body is made up mostly of segments, each of which carries both testes and ovaries. (I note, without comment, that in her Folia Parasitologica paper, Fyler describes the vagina on each segment of A. zimmeri’s body as “thick-walled, sinuous.”)

When I first discovered I was going to have a species named for me, I was overwhelmed by delusions of grandeur. But eventually I came back down to earth. My fall came in Arlington, Texas, where I had traveled to attend a meeting of the American Society of Parasitology. I got into a hallway conversation with Fyler and another cestodologist about the newly named A. zimmeri.

“Yeah, I guess that makes sense,” he said, sizing me up. “Acanthrobothrium is kind of tall and thin like you.”

Naming species was not in fact the hallowed ritual I had imagined. With so many species to name, it is actually rather routine. Fyler named the other four tapeworms Caira found in the whip ray for:

1. the ship that Caira and Jensen were on (A. oceanharvestae)

2. her grandfather, whom she called “Pop” (A. popi)

3. James Rodman at the National Science Foundation (A. rodmani)

4. Jim Romanow, who took care of the microscopes Fyler used (A. romanowi).

I’m still grateful for Fyler’s gesture, and I still can’t help but feel some vaguely paternal pleasure at seeing how A. zimmeri helps scientists learn a little bit more about the diversity of life and how that diversity evolved. Fyler and her colleagues compared A. zimmeri’s DNA to other Acanthobothrium species and discovered something interesting: the five Acanthobothrium species that they found dwelling in the single whip ray were not closely related to one another. Instead, their closest relatives live in other species of whip rays. Somehow their ancestors must have made the leap from one host to another, and somehow they must have made a place for themselves in the crowded ecosystem that is the inside of a whip ray’s gut.

For now, that leap remains almost entirely a mystery. Scientists have no idea what sort of life cycle A. zimmeri and its relatives have—what happens to the eggs that the tapeworms release from the whip rays, or what other hosts they may have to invade first before finally ending up in another whip ray. Like its whip ray host, A. zimmeri’s intermediate hosts probably have yet to get names of their own.

I hope some day scientists do figure out my namesake’s life cycle, but I also worry that their time may be running out. Whip rays, like many other rays and sharks, are in serious trouble these days thanks to reckless overfishing. And whenever one species becomes extinct, it can take other species with it. Switching host species is an exquisitely rare event, and so it’s likely that A. zimmeri can only live in one species of whip ray. When its host goes, it may disappear as well.

Now, more than ever, I feel my existence intertwined with that of parasites. Long after I’m dead, I hope that there will be whip rays swimming the Arafura Sea infested with tapeworms that bear my name.