The halt of the cassava mealybug may be a great success story, but there are stories of spectacular failure as well. The forests of Hawaii represent one. They’re filled with alien parasites brought there to destroy insect pests. Parasitic flies, for example, were brought in to keep down a species of stinkbug. But the fly could also live inside the koa bug, a big, showy native insect, and now the koa bug has almost disappeared. Parasitic wasps were brought in to control moths that attacked crops, and they also spread to many native species. Before the parasites came, the moths of Hawaii went through huge annual explosions; at their peak, their droppings falling from the trees sounded like a hailstorm. Birds would feast on their caterpillers and feed them to their young. But since the introduction of parasites, many native moths have managed to break out only once every decade or two. The forest birds of Hawaii are declining, and biologists suspect that the death of the moths may be partially to blame, because they can’t feed the birds. And without birds to pollinate the trees and disperse their seeds, the forests themselves may also be suffering.
Hawaii’s plight is the best documented of biological control’s failure because it’s a set of small, biologically distinct islands. But critics suspect that there are many other stories waiting to be told. In the United States, for example, over thirty different parasites were introduced during this century to kill gypsy moths. None of them worked well, and some of them have been destroying the exquisite giant silk moths, threatening them with extinction.
These disasters have made biologists like Lafferty and Kuris much more careful about using parasites. That was why they had set up such a long, tedious test of Sacculina in the first place. After the shore crabs started dying, they repeated their tests on Dungeness crabs. They got the same results: paralysis followed by death. “If I were to be responsible for the destruction of the Dungeness crab,” Kuris said, “my name would be mud. I would be like the guy who introduced the killer bees. The poor man has lived a life of public self-flagellation for forty years. Do I care about the native shore crabs? Sure I do. I yield to nobody on values on this.”
Lafferty broke the bad news to his colleagues in the fall of 1999. By then, the green crab had been spotted as far north as British Columbia, over a thousand miles from its landing point in San Francisco. Lafferty e-mailed me as well, and I immediately called him. I asked him if he was disappointed. “Well, as a scientist, you’re never supposed to be disappointed,” he said. “The truth exists, and you don’t have any control over what’s reality.”
But it was frustrating to watch the green crab keep spreading. “My gut feeling is that if you released these things on the West Coast, chances are they wouldn’t affect native crabs very much. All we found was that they have the potential to.” Putting Sacculina larvae in a cup with a Dungeness crab isn’t the same thing as putting them in the ocean. “It’s got to ask these questions, like where is it likely to find its host crab.”
Sacculina and its relatives use cues such as sunlight and chemicals given off by their hosts to position themselves where they’re likely to bump into a green crab. Those cues might not let them bump into any other species. Lafferty told me about another experiment he had run that supported this idea. He got his hands on another species of parasitic barnacle that is related to Sacculina and lives in the Pacific sheep crab. He then gathered California shore crabs that live in the same range as the sheep crab, but which have never been found carrying a parasitic barnacle of their own. When he exposed the shore crab to the parasite, he had no trouble infecting it. Something must be preventing the parasite from infecting the crab in the wild.
But if you’re trying to use parasites in the ocean as a biological control for the first time in history, you want to be utterly sure of yourself. I asked Lafferty if he had any other ideas for stopping the green crabs. “I don’t think we should sit back and watch the massacre,” he said. He started telling me about another parasite of green crabs called Portunion conformis. It’s an isopod, a relative of pill bugs, and it has independently evolved a Sacculina-like existence of its own in green crabs. It invades a crab as a microscopic larva and then destroys its host’s gonads, taking their place. Eventually it fills up a fair part of the crab’s body, making up a fifth of its weight. By destroying the crab’s gonads, it castrates its host, and like Sacculina, it feminizes male crabs. No one has ever cultured Portunion in a lab, but Lafferty wants to try. And then he wants to run the same tests on these parasites that Sacculina failed.
“They’re absolutely beautiful parasites,” Lafferty said. He had me picture a big, opaque pouch with a mouth at one end, carrying a collection of golden eggs inside. “It’s hard to describe them. They look like—God, they don’t look like anything you could ever imagine.” Parasites may be frustrating to work with sometimes, but for a parasitologist, there’s always a consolation in their beauty.
Herren and Lafferty work on the tattered edge of nature, the cassava fields and oyster banks where humans have transformed wilderness into a new sort of patchwork, where alien species can move thousands of miles in a matter of weeks, where the best-suited species is often the one that can thrive on perpetual chaos. Parasites may be able to soften the blow that we inflict in places like these if we respect their evolutionary power. But I also wondered about those parts of the world still left relatively untouched, and whether parasites might help keep them intact.
That was how I ended up in a Costa Rican jungle hunting frogs with Daniel Brooks. We were wandering around inside the Area de Conservación Guanacaste, a 220,000-acre reserve of dry forests, rain forests, and cloud forests, stretching from Pacific beaches to the tops of volcanoes. Twenty years ago, the forests of Guanacaste were disappearing as ranchers were cutting down trees to clear fields for their cattle, despite the fact that ranching was becoming less and less profitable. A biologist working in the area, a grizzled man named Daniel Janzen, decided to take advantage of the times. He set up a foundation that began buying up the ranches, and he hired the out-of-work cowboys to serve as “parataxonomists”—doing the work of documenting the diversity of Guanacaste by collecting species, dissecting them, and describing them. So the forest has not only been saved but expanded, and the people who live around it have a stake in protecting it. There are no fences around Guanacaste.
By the end of the 1990s, when I visited Guanacaste, Janzen was pretty much done with his reserve building. He was spending more of his time on his true love, the butterflies of Costa Rica. When you enter his little house at the reserve headquarters, three rooms under a corrugated tin roof, you have to stoop below the dozens of plastic bags hanging from the beams, each with a caterpillar feeding on a leaf. “My goal is to find all the caterpillars before I’m buried in the mud here,” Janzen said to me. Not only does Guanacaste contain a fair amount of pristine forest, but more important, in the future its forests will grow and turn into a self-sustaining ecosystem. “A thousand years from now, you come back and it’ll still be there,” he said.
One night Brooks and I burst into Janzen’s house. That day we had done a lot of dissections and looked at a lot of parasites, and we had decided to take a drive to a bar half an hour away for a drink. Along the way, the headlights of Brooks’s four-by-four lit up a furry body on the road. We stopped and backed up. It was a dead fox freshly killed, its tail still a delicate cloud of gray. It went into the back of the truck, and we headed back to Guanacaste. When we got to Janzen’s house, Brooks pulled the fox out and carried it to the front door. He laid it on the concrete floor of Janzen’s front room. The animal looked intact, but it had been hit so hard that its eyes bulged like domes out of its head. Janzen said, “Well, what do we have here?”