In the 1980s, conservationists ushered the planet's 22 last remaining Californian condors into captivity. They saved the birds, cared for them, fed them, and bred them. They also de-loused them and, in doing so, they killed off the last remaining condor louse—a harmless parasite that lived only on Californian condors. The condor population rose to over 400. The condor-louse population fell to zero. “It's a great example of a species that was knowingly, willingly, and thoughtlessly driven extinct by veterinarians,” says Kevin Lafferty, a parasitologist from the University of California, Santa Barbara. “I would hope we would act differently now.”
Lafferty is one of several scientists calling for conservationists to pay more attention to saving parasites. We view these organisms—these blood-suckers, free-riders, nutrient-drainers, and mind-controllers—with disgust and antipathy, and we're more likely to aggressively exterminate them than compassionately preserve them. But, in many cases, this kind of “taxonomic chauvinism” is a mistake.
Parasites play a critical role in ecological systems. They are abundant: In 2008, Lafferty traipsed through three Californian estuaries and found that the local trematodes—microscopic flatworms that specialize in castrating snails—outweighed all the resident fish and birds. They direct the flow of energy: A Japanese team found that trout get 60 percent of their diet from suicidal insects, driven to drown themselves in streams by mind-controlling worms inside their bodies. They keep populations of pests under control: All sap-sucking insects are targeted by some manner of parasitic wasp or fly that lays eggs inside their bodies. When we lose parasites, we lose ecological lynchpins rather than inconsequential oddballs.