May 2022, ScientificAmerican.com 65Jovelle Tamayo
reveals that parasites account for 75 percent of the links
in food webs; another study shows that they provide
us with valuable ecosystem services, including pest con-
trol estimated to be worth billions of dollars.
Like predators, parasites can exert an effect on
populations of other organisms in their habitat, which
shapes everything from nutrient cycling to the types
of plants that grow there to the abundance of top
predators. In other words, parasites “play a major role
in the natural world that was previously just over-
looked,” says Armand Kuris, a parasite ecologist at the
University of California, Santa Barbara. “Their top-
down control of populations operates differently than
predation—it’s slower—but their effect can, frankly, be
just as massive.”
Just as parasites’ critical roles are being revealed,
pioneering work conducted by Wood and others is
beginning to show that many of these important ani-
mals are in trouble. They are contending with the
same threats as better-known species: climate change,
habitat destruction, pollution, and more. Because
their fate is tied to their hosts—many of which are
also in decline—they are often doubly vulnerable, par-
ticularly if they are specialists that live on or in only
one species. “Every species you can think of that’s
endangered has parasites that rely on it,” Hopkins
explains. “If those species go extinct, then their par-
asites can also go extinct.”
But parasite conservation is a hard sell. Saving cer-tain parasites—and, in turn, preserving their roles in
nature—will depend on convincing policy makers, the
public and a wider community of scientists that pro-
tecting them is worthwhile.NOT ALL BODY INVADERS ARE BAD
ask a parasite ecologist how they got into parasites,
and they’ll likely tell you it was by accident. Wood grew
up on New York’s Long Island and dreamed of becom-
ing a marine biologist. She imagined a career spent
swimming with dolphins. In college, however, there
were no opportunities for undergraduate marine biol-
ogy research. The closest thing she could find to get on
the water was an internship collecting marine snails
infected with trematodes in New Hampshire and
Maine. The parasites interested her “in no way, shape
or form,” she says. “I wasn’t there for them.”
Wood’s mindset shifted slowly, then completely. In
parasites, she began to discover an unseen world oper-
ating in parallel to the one of free-living species. Her
undergraduate courses had hardly mentioned those
animals. “It’s possible to get a degree in biology and
never learn anything about parasites,” she says, citing
a 2011 study that found that 72 percent of 77 conserva-
tion biology textbooks either did not mention parasites
at all or only portrayed them as threats to the hosts
they occupy. As Wood learned more, she felt as though
she were waking up out of the Matrix: she could sud-
denly see a hidden layer of intricacy and connectionPAR ASITE ecolo
gist Chelsea Wood
stands among the
specimens at the
University of Wash
ington Fish Collec
tion, part of the
Burke Museum
of Natural History
and Culture.