The Surprising Secret Weapon Against Spotted Lanternflies

The spotted lanternfly is a large, visually striking insect that first showed up in the U.S. in 2014.  In just over a decade, this invasive species has multiplied across the American Northeast, with new range expansions into the Midwest and South, bringing the total number of states where they can now be found to 19, as well as the District of Columbia. 

Not only do they feed on plant sap and harm trees, but spotted lanternflies also pose a threat to the grape and wine industry, among many other crops. Scientists have recently said that squashing them likely won’t make a dent in their populations. 

However, they may have stumbled upon a new weapon in the fight against the invasive species—one that just so happens to be critical habitat for monarch butterflies, an insect species perhaps as loved as the lanternfly is despised: 

Milkweed. 

When spotted lanternflies feed on the stuff, they have a tendency to drop dead.

“We were planning to run the experiment for a week, except when we went back the next day, the majority of the lanternflies that were on milkweed were dead,” says Anne Johnson, a postdoctoral researcher at Michigan State University. 

There have been many different solutions proposed for the spotted lanternfly invasion, including pesticides, parasitic wasps, and sticky tapes. (Read more: “Inside the race to kill an invasive menace—before it gets to a town near you”)

But the potential benefits of milkweed in controlling the insects wasn’t something scientists dreamed up in a lab. “It really started with people paying attention to what was happening in their yards,” says Sara Hermann, an associate professor of entomology and ecology at Penn State University. 

Back when Johnson was completing a Ph.D. at Penn State, she ran a citizen science survey that asked everyday people to submit observations about what animals were preying upon spotted lanternflies. But the project, called Birds Biting Bad Bugs, also yielded a surprising amount of people saying they were finding dead lanternflies under their milkweed plants.

At the same time, Hermann, who studies milkweed and monarchs, was hearing the same story from a different segment of the public. “We thought, ‘Well, this is something we can actually test. You have spotted lanternfly, and I have milkweeds. So why don't we just put them together and figure out if this is real?’” says Hermann. “Like, wouldn’t that be crazy?”

While the results have not yet been published, the experiment was pretty straightforward. Hermann and Johnson set up a series of enclosures where spotted lanternflies were given access to either various species of milkweed, grapevine (a treasured lanternfly food), or no plants. 

“What we saw is that lanternflies exposed to milkweed had a substantially higher mortality than the lanternflies when they were given grape,” says Hermann. 

While this all makes logical sense—monarch butterflies are able to absorb toxins in milkweed that in turn make them taste bad to predators—the researchers admit that they have not yet figured out what in the plants’ chemistry is lethal to lanternflies.

Even if the results aren’t fully confirmed, the researchers say planting milkweed is a great idea for a few reasons. For starters, there are dozens of species of milkweed native to the U.S., and each is important for native pollinators, including the monarch butterfly. While swamp milkweed (Asclepias incarnata) wasn’t quite as effective at killing lanternflies as common milkweed (Asclepias syriaca), the former is preferred by farmers and gardeners because it doesn’t spread as willingly. (While milkweeds are native, they have historically been removed by farmers because of the way they can outcompete food crops.)

While Hermann and Johnson say there’s much more work to be done, both find the results of the preliminary study exciting.

“The magnitude of mortality, I would say, depends on the life stage [of the lanternfly] and the species of milkweed,” says Hermann. “It's kind of complex, but we saw anywhere from 10 to 90 percent mortality within just 24 hours.”

Adult lanternflies and nymphs in the last stage before adulthood—likely the ages of spotted lanternflies in your yard right now—were hardest hit by the milkweed, she says.

In the experiment, there were also treatments where the lanternflies could choose between grapevines and milkweed. Surprisingly, some spotted lanternflies chose to feed upon the milkweed and die, even though they had the option to eat grapevine instead. Scientists say this may be because lanternflies are cosmopolitan in their tastes—they’ll try nearly anything.

“It’s likely because there are no milkweeds in their native habitats,” says Brian Eshenaur, a plant pathologist with Cornell University’s Integrated Pest Management Program who was not involved in the research. “So, it doesn’t know not to feed on it.” 

“I've even seen them attempt to feed on telephone poles, just because it kind of looks like a tree to them,” says Johnson.

This gives the researchers hope that enough lanternflies will feed on milkweed out in the world, even when there are other plants to choose from. Combined with Johnson’s earlier research—showing that everything from birds and spiders to mantises, snakes, and yellowjackets are now feasting on spotted lanternflies—it suggests that there are more allies in this fight than they might have originally thought.

“You know, there's going to be no silver bullet for something like this,” says Hermann. “But if we can create habitat where predators exist and where options like milkweed exists, then we know that we're already putting our best foot forward in terms of managing these insects. And a lot of that comes down to planting native plants, which is really cool.”