Estelle Caswell/Grist
This story was originally published by Grist and is reproduced here as part of the Climate Desk collaboration.
When Chelsea Wood was a child, she would often collect Periwinkle snails on the shores of Long Island.
“I used to pluck them off the rocks and put them in buckets and keep them as pets and then re-release them,” Wood said. “And I knew that species really well.”
It wasn’t until years later that Wood learned that those snails were teeming with parasites. “In some populations, 100 percent of them are infected, and 50 percent of their biomass is parasite,” Wood said. “So the snails that I had in my bucket as a child were not really snails. They were basically trematode [parasites] that had commandeered snail bodies for their own ends. And that blew my mind.”
Wood, now a parasite ecologist at the University of Washington, sometimes refers to parasites as “puppet masters,” and in many cases, it’s not an exaggeration. Some can mind-control their hosts, for example, causing mice to seek out the smell of cat pee. Others can shape-shift their hosts, physically changing them to look like food. And their ripple effects can reshape entire landscapes.
For centuries, people have thought of parasites as nature’s villains. They often infect people and livestock. In fact, parasites are by definition bad for their hosts, but today, more scientists are starting to think about parasites as forces for good.
“I don’t think anyone is born a parasitologist. No one grows up wanting to study worms,” Wood said. “Somewhere along the way, I like to say, they got under my skin. I just fell in love with them. I couldn’t believe that I’d gotten that far in my biology education and no one had ever mentioned to me that parasites are incredibly biodiverse, ubiquitous, everywhere.”
On a cloudy August morning, Wood took me to Titlow Beach in Washington state, one of her team’s research sites. Back in the 1960s, one of Wood’s research mentors had sampled shore crabs here. At the time, the area was very industrial and heavily polluted. But when researchers, including Wood, came back to collect samples half a century later, the beach had transformed. The water was cleaner and the shorebirds had returned, but those weren’t the only promising signs: The crabs were now full of trematode........