To the study of parasites, Phillips has often given blood, sweat, and tears—sometimes, very literally. For example, she collects leeches “in the usual way”—by finding the right watery habitat, donning shorts, wading in, and making a lot of movement. The leeches come to her. When one bites, she has to lift her leg very slowly because some of them will drop off if they leave the water too quickly. “This is why I do yoga,” she tells me.

Leeches are exceptional, though. In most cases, to collect a parasite, you need to collect its host. Kayce Bell studies the parasites of mammals, and she’s spent a lot of time trapping chipmunks. After euthanizing the animals, she plucks them of fleas, mites, ticks and lice, and then systematically dissects them, scanning every gastrointestinal organ for tapeworms, flukes, and more. Each rodent is more than just an individual: It’s a world, ripe for exploring. “I can do a chipmunk in about 30 minutes,” she says.

This work matters, because parasites are ecologically vital, and poorly studied. And much like the rest of nature, they’re in danger. As hosts die, so do their parasites—and sometimes, conservationists deliberately usher the latter into oblivion. In one notable case, the same people who saved the Californian condor from extinction also wiped out the harmless condor louse, by delousing the last surviving birds.

Humans can also make things harder for parasites in subtler ways. Many of these creatures have free-living stages, where they travel through the world in search of hosts. On these journeys, they’re vulnerable to the same changes in temperature and rainfall that are affecting the entire planet. Global climate change is also forcing animals to move into new areas; that could be a problem for the parasites that depend on those animals, especially if they have complex life cycles that involve several hosts.

Phillips and a team of like-minded scientists recently used the National Parasite Collection to simulate these changes, by looking at how the whereabouts of parasite groups have shifted over time, and how those ranges relate to climate. They estimated that between 5 and 10 percent of parasite species will go extinct by 2070 because of climate change, as will 30 percent of parasitic worms.

These are conservative figures, born of research that has been heavily skewed toward North America, says Carrie Cizauskas from the University of California, Berkeley, who was involved in the study. “There’s hardly any data across Africa. There’s very little parasite research in global-biodiversity hot spots, which are also likely to be parasite-biodiversity hot spots.” With a more detailed portrait of our parasitic planet, Cizauskas says that scientists can work out which groups are most in need of saving.

The very concept of saving parasites is so counterintuitive that Cizauskas and her colleagues found it hard to publish their studies on parasite extinction risk. Reviewers would say, “Why should we conserve these things that everyone thinks are gross?” This attitude seems especially trenchant, but as I’ve written before, history suggests that it can change. Microbes were once seen as germs; now, we’re starting to appreciate how important those in our bodies are for our health. Top predators were once seen as competitors or trophies; now, conservationists talk about protecting or even reintroducing them. Parasites could get the same reputational makeover.

“People ask me if I dreamed about being the curator of the National Parasite Collection when I was five,” Phillips says. “No, not at all. But dreams change over time.”

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