The Unsung Heroes of Ecosystems: Parasites
A Change in Perspective
For centuries, parasites have been vilified as nature’s antagonists, often associated with disease and harm to humans and livestock. However, a growing number of scientists are beginning to recognize the vital role parasites play in maintaining healthy ecosystems. Chelsea Wood, an assistant professor at the University of Washington, likens parasites to “puppet masters,” shaping the behavior and physical characteristics of their hosts in ways that can have far-reaching effects on entire landscapes.
The Bellwether of Ecosystem Health
During a visit to Titlow Beach in Washington state, Wood explained how the presence of trematode worms, a type of parasite that alternates between crabs and birds, signaled the recovery of the local shorebird population. As scientists have delved deeper into the world of parasites, some have proposed that many ecosystems might actually require them to thrive. Wood stated:
“Parasites are a bellwether. So if the parasites are there, you know that the rest of the hosts are there as well. And in that way they signal about the health of the ecosystem.”
Drawing Parallels with Predator Ecology
To grasp this counterintuitive concept, it’s useful to consider another group of animals that were once despised: predators. In the past, communities often treated predators as pests, encouraging hunters to eliminate wolves, bears, coyotes, and cougars to safeguard themselves and their property. However, the consequences of this approach became evident, particularly in Yellowstone National Park.
When gray wolves were systematically eradicated from Yellowstone in the 1920s, the elk population grew unchecked, leading to overgrazing near streams and rivers. This drove away native beavers, causing ponds to disappear and the water table to drop, ultimately transforming the entire landscape. The reintroduction of gray wolves in the 1990s brought about a remarkable change, with a “wave of green” rolling over the park. This story became a defining parable in ecology, demonstrating that predators weren’t merely killers but essential components in holding ecosystems together.
The Profound Impact of Parasites
Just as with the gray wolves in Yellowstone, scientists are beginning to recognize the significant ways in which parasites shape ecosystems. One example is the relationship between nematomorphs, a type of parasitic worm, and creek water quality. These worms are born in water but spend their lives inside land-dwelling insects like crickets or spiders.
At the end of their lives, nematomorphs need to return to the water to mate. Instead of making the perilous journey themselves, they manipulate their infected hosts into providing transportation by inducing a “water drive”—an impulse that compels the insect to immerse itself in water, leading to its demise but benefiting the parasite.
The story doesn’t end there. The entire creek ecosystem relies on this worm’s quest to reach the water. Fish consume the insects that throw themselves into the water, with one endangered trout species deriving 60 percent of its diet exclusively from these infected bugs. In essence, the parasite is sustaining this endangered trout population. With a reduced threat from hungry fish, native insects in the stream can flourish, consuming more algae and contributing to clear creek water.
The Unexplored World of Parasites
Despite making up an estimated 40 percent of the animal kingdom, scientists know very little about millions of parasite species worldwide. The primary focus of research has been on parasites that infect farm animals, pets, and humans. Many of these concerning parasites, such as ticks or the parasitic fungus responsible for Valley fever, are expected to increase due to climate change. However, the broader implications of climate change on parasites and how significant changes in parasites might reshape the world remain largely unknown.
Wood had an innovative idea to address this knowledge gap: examining a collection of preserved fishes stored in a museum basement. The University of Washington Fish Collections houses over 12 million samples of preserved fishes dating back to the 1800s, along with all the parasites living inside them.
Wood and her team spent over two years meticulously dissecting parasites from the preserved fish samples, identifying and counting them under microscopes before returning everything for future study. In total, they discovered more than 17,000 parasites.
The Decline of Complex Parasites
By analyzing the number of parasites found in fishes over time, the researchers identified a mix of winners and losers. However, one major class of parasites stood out as unequivocally declining: complex parasites, which require multiple host species to survive. On average, this type of parasite decreased by 10 percent each decade.
Wood’s investigation revealed that climate change was the sole factor that perfectly explained the decline in parasites, rather than chemicals or overfishing. Complex parasites can only survive if all of their host species are present. The absence of even one type of host spells the end for the parasite. Wood explained:
“That’s why we think that these complex life cycle parasites are so vulnerable: because things are shifting, and the more points of failure you have, the likelier you are to fail.”
Prior to this study, researchers were unaware that climate change was eradicating this crucial class of parasites.
The Importance of Understanding Parasites
Wood emphasizes the significance of recognizing the vast and intricate roles parasites play in nature. Ignoring what we cannot see puts us at risk of failing to comprehend how the world truly functions. She stated:
“We all have a reflexive distaste for parasites, right? We take drugs, we apply chemicals, we spray. Our argument is that parasites are just species. They’re part of biodiversity, and they’re doing really important things in ecosystems that we depend upon them for.”
As we continue to explore the fascinating world of parasites, it becomes increasingly clear that these often-overlooked organisms are not merely nature’s villains but rather unsung heroes that play a vital role in maintaining the delicate balance of our ecosystems.
5 Comments
Parasitic worms, beneficial? Finally, a diet trend that’ll really get under your skin!
Introducing worms for health: seems Mother Nature does have a twisted sense of humor after all!
Worms as wellness warriors? Sounds like we’re wriggling into strange territory!
Parasitic worms as health boosters? Nature’s weirdest joke on us, I guess.
Worms for wellness, huh? That’s one slippery slope of a health trend!