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Blowtorching spotted lanternflies is, in fact, a bad idea

What the war on invasive lanternflies gets wrong.

A smashed spotted lanternfly on the ground in New York on August 24.
| AP

If you see a spotted lanternfly, kill it. Immediately. And without hesitation.

That’s our civic duty, according to state officials in New York, Pennsylvania, and other states where these invasive species — which are neither flies nor moths but a type of insect known as a planthopper — have multiplied in recent years.

The kill-on-sight order is rooted in a legitimate concern. Spotted lanternflies drink the sap of dozens of different plants, including commercial ones like grapevines. They can weaken and sometimes kill crops, putting foods (and the revenue they generate) at risk.

A wanted poster that the Pennsylvania Department of Agriculture tweeted earlier this month.
Pennsylvania Department of Agriculture

So we stomp them. We squash them. We go on lanternfly-killing bar crawls.

But some people have taken killing these winged insects to extremes. They’ve burned trees with flame throwers, doused plants in pesticides, and crafted homemade bug-killing concoctions (that kill a lot of other stuff, too).

Experts warn that these extreme efforts are likely doing more harm than good.

“There are people who are dumping all sorts of pesticides on these guys and not following proper procedures, or lighting things on fire to try to get rid of them,” said Anne Johnson, a doctoral researcher at Penn State University who studies spotted lanternflies. “You don’t need to be that extreme. You are probably causing more damage that way.”

Scientists have also learned that lanternflies are not as harmful as they once feared, according to Brian Walsh, a horticulture educator at Penn State Extension who’s been researching lanternflies for years. The insects typically don’t kill trees, nor are they likely to harm humans or pets directly (though there are some reports of pets getting nauseated or lethargic after eating them, Johnson said).

That doesn’t mean you should stop squishing them. It could still help limit the impact, Johnson said. But ultimately, managing the lanternfly fly problem comes down to something much bigger: restoring degraded ecosystems that have allowed these pests to thrive in the first place.

A one-of-a-kind killing campaign

The spotted lanternfly, native to parts of Asia, was first discovered on American soil in the fall of 2014, in eastern Pennsylvania. Because the insect threatens farms and the local environment, researchers dubbed it an “invasive species,” instead of using the more neutral term “nonnative.”

Lanternflies have since proliferated. They’ve spread to at least 14 states, from Delaware to Indiana, and are now in major cities including New York, Philadelphia, and Wilmington (where one landed, iconically, on President Joe Biden). Typically, you’ll just encounter one or a handful of them, but they can occasionally swarm, especially around certain trees.

New York State Integrated Pest Management Program

When researchers first detected lanternflies, they thought they might be able to eradicate them from the US altogether, Walsh said. At the time, people thought lanternflies depended on one kind of tree, which biologists could remove, and that, despite having wings, they couldn’t really fly, he said.

Neither of those beliefs has proved to be true.

Nonetheless, it was that goal of eradication that fueled the public campaign to kill every last one of them, Walsh said. And messaging from that campaign — which has attracted a huge amount of media buzz — has, in turn, inspired “a lot of bad actions,” Walsh said, referring to the extreme lengths some people have gone to get rid of the insects.

In at least some cases, people in Pennsylvania have run blowtorches up and down their trees, he said, which can damage the plant and other animals living on it. “Anyone who goes out and buys a propane torch ... don’t,” Johnson said.

Other people, aggravated by the bugs, have doused trees with pesticides and homemade concoctions, some of which involve gasoline or dish soap, Walsh said. “Don’t try to make your own formulations,” Johnson said. “A lot of those can hurt your plants or kill other things in the area.”

In one case, someone complained to Walsh that spotted lanternflies were killing a tree in her yard. After careful inspection, he realized that she had mistakenly sprayed the tree with an herbicide — glyphosate, a potent chemical designed to kill plants — instead of a pesticide, as journalist Abigail Gruskin reported for the Atlantic.

Walsh, who used to run a large landscaping business, has also fielded complaints from his clients that lanternflies killed their trees when, in fact, another invasive species — the emerald ash borer — was most likely to blame.

In reality, it’s not clear that any efforts by average citizens have helped stem the spread of lanternflies. “Look, we’re not going to eradicate them,” Walsh said. “We need to look at this as more of a chronic problem.”

How bad are these bugs, really?

Spotted lanternflies can harm trees in a few ways. They steal nutrients by sucking down sap, much like a parasite, and they create holes in the plant through which pathogens can enter, Johnson said. They also exude a sugary liquid called honeydew as they drink, which can attract sooty mold that can harm the plants as well.

Researchers from Penn State have tried to put a number on the potential damage that lanternflies can cause. In a study published a few years ago, they concluded that lanternflies could cost Pennsylvania’s economy at least $324 million a year, and potentially upward of $500 million a year, if the insects weren’t held in check.

Spotted lanternflies on a tree in District Township, Pennsylvania.
Harold Hoch/MediaNews Group/Reading Eagle via Getty Images

Another recent study found a link between infestations of lanternflies in vineyards and a drop in grape production and vine health in the Northeast. There are also reports of lanternflies decimating entire vineyards.

But aside from their impacts on grapevines, spotted lanternflies are not as harmful to commercial crops and forests as scientists once feared, Walsh said. “It’s not destroying all of our crops,” he said of the invasive species.

There’s another important point here: Ecosystems are complicated, so introducing a new species can have all kinds of unexpected impacts.

The honeydew that lanternflies produce, for example, may actually be a food source for honeybees and other nectar-seeking insects. One company in Pennsylvania has even started selling honey with a unique flavor apparently influenced by spotted lanternfly honeydew, called “Doom Bloom,” as reporter Alexandra Jones wrote for Atlas Obscura.

Praying mantises are among the many predators known to catch and eat spotted lanternflies.
Courtesy of Jeffrey W. Doelp

Johnson’s research has also shown that a number of predators, from birds to small mammals, are feasting on lanternflies. One complicating factor is that the tree of heaven, a lanternfly favorite, produces a host of toxins that could end up in lanternflies and their honeydew. Johnson is doing research to understand if predators tend to avoid eating lanternflies that feed on the tree of life.

A problem of our own making

Spotted lanternflies are a problem because we brought them here (likely as eggs on a cut stone shipment). The introduction of nonnative species is an unfortunate and common side effect of globalization.

But that’s just part of the story. Not only are lanternflies here in the US but they’ve been able to thrive — and that’s due, in part, to much broader ecological disturbances.

The tree that lanternflies seem to be most attracted to is the tree of heaven, which is from Asia and is actually another invasive species. Lanternflies use the tree to feed, and they often lay their eggs on its bark. The tree of heaven grows easily in urban environments where other trees have been cut down, such as along railroads. By changing ecosystems, humans have allowed the tree of heaven to multiply, which is now helping to sustain populations of lanternflies.

These invasive insects also face little competition for food and few predators. Both native birds and insects have declined dramatically over the past several decades, largely due to the destruction of ecosystems.

So, ultimately, to control lanternflies humans may have to restore ecosystems. That could mean getting rid of other invasive species and planting native trees and other plants that attract predatory birds and native bugs, Johnson said. A fully functional, restored ecosystem is likely to be more resistant to infestations of spotted lanternflies.

Then again, it’s unlikely that we’ll ever wipe out lanternflies altogether — it’s rare to completely eliminate any invasive species. Instead, we’ll have to learn to live with them, just as we do with the more than 6,000 nonnative species in the US. That means more squishing. More trapping. More egg scraping. Though, in any case, a flame thrower is not the answer.

Kim Mas contributed reporting to this article.

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