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 worms, a type of parasite that jumps between crabs and birds.

Chelsea Wood kneels to search for shore crabs at a beach in Tacoma, Washington. She will later dissect the crabs to search for parasites. Jesse Nichols / Grist

The parasites were a sign that the local shorebirds were doing great, Wood explained.

As scientists have learned more about parasites, some have argued that many ecosystems might actually need them in order to thrive. “Parasites are a bellwether,” she said. “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.”

To understand this counterintuitive idea, it’s helpful to look at another class of animals that people used to hate: predators.

For years, many communities used to treat predators as a kind of vermin. Hunters were encouraged to kill wolves, bears, coyotes, and cougars in order to protect themselves and their property. But eventually, people started noticing some major consequences. And nowhere was this phenomenon more apparent than in Yellowstone National Park.

In the 1920s, gray wolves were systematically eradicated from Yellowstone. But once the wolf population had been eliminated from the park, the number of elk began to grow unchecked. Eventually, herds were overgrazing near streams and rivers, driving away animals including native beavers. Without beavers to build dams, ponds disappeared and the water table dropped. Before long, the entire landscape had changed.

In the 1990s, Yellowstone changed its policy and reintroduced gray wolves into the park. “When those wolves came back in, it was like a wave of green rolled over Yellowstone,” Wood said. This story became one of the defining parables in ecology: Predators weren’t just killers. They were actually holding entire ecosystems together.

“I think there’s a lot of parallels between predator ecology and parasite ecology,” Wood said.

Like the gray wolves in Yellowstone, scientists are just starting to recognize the profound ways that ecosystems are shaped by parasites.

Chelsea Wood holds a jar of fish that her lab dissected for a study published in 2023. Jesse Nichols / Grist

Take, for example, the relationship between nematomorphs, a type of parasitic worm, and creek water quality. The worms are born in the water, but spend their lives on land inside of bugs, like crickets or spiders.

At the end of their lives, nematomorphs need to move back to the water to mate. Instead of making the dangerous journey themselves, they trick their infected hosts into giving them a ride by inducing a “water drive,” an impulse on the part of its insect host to immerse itself in water. The insect will move to the edge of the water, consider it for a little while and then jump in — to its own death, but to this parasite’s benefit.

The story doesn’t end there. In a way, the entire creek ecosystem relies on a worm trying to hitch a ride to the water. Fish eat the bugs that throw themselves in the water. In fact, one species of endangered trout gets 60 percent of its diet exclusively from these infected bugs. “So essentially, the parasite is feeding this endangered trout population,” Wood said.

With less of the threat associated with hungry fish, the native insects in the stream can thrive, eating more algae and thereby giving the creek clear water.

Parasites make up an estimated 40 percent of the animal kingdom. Yet, scientists know next to nothing about millions of parasite species around the world. The main parasites that scientists have spent a lot of time studying are the ones that infect farm animals, pets, and people.

Many of these alarming parasites, like ticks or the parasitic fungus that causes Valley Fever, are expected to increase due to climate change. But no one actually knows what climate change means for parasites, broadly — or how any big change in parasites might reshape the world. “There’s this general sense that infection is on the rise, that parasites and other infectious organisms are more common than they used to be,” Wood said. “At least for wildlife parasites, there really isn’t long-term data to tell us whether that impression that we have is real,” Wood said. “We had to invent a way to get those data,” Wood said.

Wood had an unconventional idea of where to look: a collection of preserved fishes locked away in a museum basement.

Chelsea Wood holds a jar of preserved fish from the University of Washington Fish Collections. Jesse Nichols / Grist

The University of Washington Fish Collections is home to more than 12 million samples of preserved fishes, dating all the way back to the 1800s. But the thousands of jars lining the collection shelves also contain something else: all the parasites living inside the fish samples.

“So much has been discovered from museum specimens that we tucked away at one time, and then pulled off the shelf 100 years later,” said Wood. “It’s really remarkable to get to peer back in time the way that you do when you open up a fish from a hundred years ago. It’s the only way that we’ll know anything about what the oceans were like, parasitologically, that long ago.”

Chelsea Wood dissects fish samples in her lab at the University of Washington. Jesse Nichols / Grist

Wood and her team spent over two years opening up jars and surgically dissecting the parasites from within. Under microscopes, they identified and counted the parasites before returning everything for future study. In the end, they found more than 17,000 parasites.

Looking at the number of parasites found in fishes over time, the researchers found a mix of winners and losers, but there was one big class of parasites that was unequivocally declining: complex parasites, the kinds that need several different host species in order to survive. That type of parasite declined an average of 10 percent each decade, the team found.

Jesse Nichols/Grist

In Wood’s investigation, there was only one factor that perfectly explained the decline in parasites: It wasn’t chemicals or overfishing. It was climate change. It made a lot of sense: Complex parasites can only survive if everyone one of those host species are around. If just one type of host goes missing? “Game over. That’s it for that parasite,” Wood said. “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.”

Wood said that, before this study, researchers had no idea climate change was wiping out this important class of parasites.

“It’s likely a collateral impact,” she said. “We don’t even have a handle on how many parasites there are in the world, much less the scale of parasite biodiversity loss right now. But the early indications are that parasites are at least as vulnerable as their hosts, and potentially more vulnerable.”

Wood says that it’s important for people to understand that parasites play huge and complex roles in nature, and if we ignore what we can’t see, we risk missing out on understanding how the world really works. “We all have a reflexive distaste for parasites, right? We take drugs, we apply chemicals, we spray, Wood said. “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.”

This article originally appeared in Grist at https://grist.org/video/parasite-climate-change-ecosystem-health-science/. Sign up for Grist’s weekly newsletter here. Grist is a nonprofit, independent media organization dedicated to telling stories of climate solutions and a just future. Learn more at Grist.org

The post Nature Can’t Run Without Parasites. What Happens When They Start to Disappear? appeared first on Modern Farmer.

By literally wiping out tons of pests every night, bats save US farmers an estimated $3.7 billion annually. Besides the bug carnage, bats also pollinate crops such as coconuts, agave, guava and bananas, disperse seeds and create fertilizer. 

However, these little mammals are under attack—more than half of North American bats risk severe population declines over the next 15 years. And agriculture, which destroys foraging and roosting habitat, is one of the greatest threats to bats. 

Yet farmers can be important allies for wildlife by using innovative practices to conserve bats. In turn, this mammalian air crew protects and pollinates their fields.

Pests and heirloom produce

“I know a lot of people are kind of freaked out by the bats but they are invaluable in sustainable agriculture—absolutely invaluable,” says Stephanie Miller, owner of Mystic Pine Farm in Virginia, which specializes in organic heirloom crops from the African diaspora.

Her farm is bustling with bat activity for several reasons.

“We don’t obviously use any chemicals because that’s also a main deterrent and that will definitely get rid of your bat population very quickly,” says Miller. 

Besides directly poisoning bats, pesticides and insect-resistant crops reduce the abundance of their prey. 

A wooded area on Mystic Pine Farm in Virginia. (Photo courtesy of Stephanie Miller)

Miller also maintains oaks on her property to provide roosts for the bats and intentionally supplies food for her winged guests. 

“I grow night-blooming plants that attract the bats and give them nectar and feed them,” says Miller. “Also, I grow species of native plants and what I would consider medicinal herbs that they also like to feed off of or attract the food that they eat—things like purple coneflower, yucca and sunflowers.” 

Research backs these observations up: Lower-intensity practices such as agroforestry and organic farming support higher bat activity levels and diversity compared to more intensive agriculture.

Factors at the landscape level also come into play.

“You should always leave as much natural habitat as possible around your farms,” says Merlin Tuttle, a bat researcher and founder of Merlin Tuttle’s Bat Conservation. “Where pests do the worst damage is where you have huge monocultures, where for miles and miles you have nothing but corn or soybeans or wheat planted. And in those cases, bats and other natural predators can’t survive the off-season. After you harvest the corn or the wheat, there’s no pests out there to eat.” 

In turn, Miller benefits from having bats around.

“I’m using nature, including the bats, to control my pest population,” says Miller. “And bats do a lot of work. They actually pollinate certain crops. They also eat pests that might be an issue and keep those populations under control.”

For instance, bats kill corn earworms, a major pest of popcorn and one of Miller’s main crops. 

“I’m using nature, including the bats, to control my pest population,” says Virginia farmer Stephanie Miller. (Photo courtesy of Stephanie Miller)

Pecan protection 

While Miller exemplifies a bat-friendly farmer, she’s not alone. Through Merlin Tuttle’s Bat Conservation and Bat Conservation International, pecan farmers are learning how to cut down on pests by installing bat houses.

One example is John Worth Byrd, owner of a sustainable pecan farm in central Texas.

“We have three moth-born pests here, the walnut caterpillar, the pecan nut casebearer and the hickory shuckworm,” says Byrd. “But the bats, their primary food is moths. So, I thought, well that’s great. Some people in Georgia had done it, put bat houses into their pecan orchards. So, I started putting up bat houses.” 

Byrd has five species of bats on his property. Some forage in wide open spaces away from their roosts, while others dine locally in the orchard canopy. While all the bats suppress pecan pests, the locavores kill the most. 

Byrd uses a couple of strategies to help his bats. Besides putting up bat boxes, he doesn’t spray any pesticides on his property. In addition, if a tree dies in his orchard, he leaves it up. 

“A lot of these bats roost in these old dead pecan trees…” says Byrd.

“The best bats were staying in these cavities, not as many numbers like the [Brazilian] free tails in my houses, but they were doing a lot. They were local feeders instead of feeding in the atmosphere.” 

Unsurprisingly, all this pest-munching is valuable.

“If people could actually see what bats are doing, they’d be lined up to protect them,” says Tuttle. “It’s estimated by our Parks and Wildlife Department here in Texas that consumption of insect pests is saving Texas farmers approximately $1.4 billion annually.”

Aiding agaves

One of Mexico’s most iconic products has also jumped on the bat conservation bandwagon.

Through the Tequila Interchange Project, tequila and mezcal producers are growing bat-friendly agaves. These spiky plants are normally cloned, but letting some of them flower has several advantages. Night-blooming flowers provide nectar for bats, including an endangered species, the Mexican long-nosed bat. By feeding on the flowers, bats also pollinate them.

Commercial farming of blue agave, used for tequila, has eroded its genetic diversity and increased its susceptibility to disease. For instance, in the 1990s, a combination of bacteria and fungus spread through agave fields, and nearly 25 percent of the crop was abandoned.

This hasn’t gone unnoticed by agave farmers. 

“They understand that something is happening,” says Irene Zapata Moran, a doctoral student at the University of Wyoming. “They see that there are more diseases in the crops. And people who have been in this industry all their life, they have told me they remember before that the plants used to be bigger.”

A lesser long-nosed bat feeds on an agave blossom in Arizona. (Photo: Shutterstock)

Bat pollination is seen as a solution, because as opposed to cloning genetically identical plants, sexual reproduction brings in new genes. This could also increase the plant’s ability to adapt to climate change.

However, allowing for natural pollination of agaves involves a direct financial hit for farmers. 

Farmers normally cut the flower stalks on the agave to allow the sugar to be concentrated in the core. After harvesting, they use this core for tequila production. 

“They’re completely rivals—you cannot have agaves in bloom and tequila from the same plot,” says Zapata Moran.

One solution could be for tequila producers to charge a premium price for bat-friendly products. Offsetting just a portion of their sunken costs could be an effective way to incentivize farmers who may not be motivated to give up some of their crops in the name of biodiversity.

The vast swaths of cropland and pasture blanketing the globe present a golden opportunity for bat conservation. And, with more than 18 percent of species listed as threatened globally, bats need all the help they can get. While sustainable practices require funding, cost-sharing programs, such as those from the USDA Natural Resources Conservation Service, can help farmers. Plus, the payoff is worth it—bats are an eco-friendly solution for many agricultural woes.

The post Agriculture Threatens Bats. These Farmers Want to be Part of a Solution. appeared first on Modern Farmer.