This fall, spotted lanternflies have been seen all around campus. These colorful bugs are an ever-growing problem, both on Swarthmore’s campus and in the country. These invasive pests are putting undue strain on native plant species and even forcing some vineyards to close down. Spotted lanternflies, a species native to China, first appeared in the U.S. in Berks County, PA, in 2014, and came to Swarthmore around 2016. The lanternflies have continued to grow in population and have spread into fourteen other states, including New York, New Jersey, and Maryland.
In an interview with The Phoenix, Jeff Jabco, director of grounds and coordinator of horticulture at the Scott Arboretum, talked about the lanternfly infestation on campus.
“This year, [the invasion has] been quite severe with high populations. Last year seemed to be much less … 2022 was high. 2021 was low. 2020 was high,” he said.
Lars Rasmussen, integrated pest coordinator at the Scott Arboretum, explains they first appeared around the railroad tracks because one of their favorite trees, the invasive Tree of Heaven, tends to grow there.
“I knew how [these pests] got introduced, so I was always looking up by the railroad tracks … I think I was the first one to see them on campus,” he said.
When lanternflies feed on trees, they leave lesions from which sap flows and attracts other insects. They also excrete a sugary substance while eating called honeydew, which causes sooty mold development on trees. These factors can cause long-term weakening of trees, which makes lanternflies plant stressors.
“They don’t harm people, they don’t bite, they’re just a nuisance ,” Rasmussen explained. “You have a plant or a tree, that’s under pressure [from] other bugs or disease and they can be that maybe one thing that puts it over the edge.”
Swarthmore College is home to many of the plants these bugs are attracted to. These include the Tree of Heaven, Red Maple, Black Walnut, Virginia Creeper, Oriental Bittersweet, and Styrax. Rasmussen went on to explain how the lanternflies feed from these trees.
“They feed really lazily, they can stick through stylets into the tree and then this goes into them, it’s not like they’re sucking, it’s just like the trees pressure or turgor pressure goes to feed into them and then it goes right through them and that’s why they make so much honeydew,” Rasmussen said.
Rasmussen further explained that, while the harmful effects of lanternfly infestation will not cause immediate environmental devastation, there is a chance of trees dying from extended stress due to lanternflies feeding on them for multiple years.
“So if I’m looking at a large population of lanternflies, they rarely will kill a tree. They will possibly in large numbers kill a small Black Walnut. They will [kill] Tree of Heaven in certain situations,” he said.
In addition, perennials, which often grow under trees, can suffer from sooty mold development and die.
“Another concern, being an arboretum, you have a lot of things that are planted underneath, and you’ve got a lot of honeydew which makes black sooty mold which possibly will kill a bunch of perennials underneath, which might be another concern you have to think about,” he said.
The Scott Arboretum is using many techniques to cull the lanternflies. One method for removing lanternflies, Rasmussen said, is killing all but one Tree of Heaven and using it as a “trap tree” to attract lanternflies before killing them with a pesticide sprayed on the tree. Since the Tree of Heaven is itself an invasive species, Rasmussen is able to kill almost all of them, and use the few remaining as trap trees, but he still prefers to use this method sparingly because of the effects of pesticides.
“I do use pesticide to treat two Ailanthus [Tree of Heaven] trees as trap trees. So I will use a systemic pesticide. But if I have to use [pesticides], it’s the last thing to use,” he said.
Another method Swarthmore is using is cutting out plants, like the Virginia Creeper, to remove the flies’ food source. Jabco explained how this technique works.
“We used to have some Virginia Creeper over on the barn. It was just covered by lanternflies. So we just cut it all down … now it will grow back. But if a lanternfly keeps being attracted to it, the idea is that you don’t want to have something that they’re going to be attracted to and feed on. So if we get rid of some of their food sources, then there might be a lower population. And we don’t want to do that with our native plants,” he said.
This strategy, and many others, are untenable for native or protected species. Even other methods, like sticky bands, can be complex and problematic, as traps must be placed at the right time of year and the right type of tree. Sticky bands are most effective on trees with smooth bark or when lanternflies are in the nymph stage of development as they crawl up and down trees and stick to the trap. But it’s critical to make sure that the sticky traps don’t accidentally attract pollinators and interfere with the pollination of trees.
A third method that’s particularly effective is killing nearby egg masses that lanternflies lay on trees or other flat surfaces. This can be done by scraping the egg mass off into an alcohol solution or smashing them. Rasmussen explained lanternfly egg laying has started, and will occur until November, so this method will be actively utilized for the next few months.
“I just smash them off with my thumb, or you can scrape them off into a bag with a little bit of hand sanitizer … They’ll start laying eggs very soon and they’ll lay eggs all the way into November, until the freeze,” he said.
The grounds and horticulture staff also use horticultural soap. Since the eggs are protected in a mud-like covering, this technique dries out the egg clumps to kill them, as opposed to just smashing them.
“Horticultural soap, or a horticultural oil, or a spray, on the eggs, it’s gonna dry them out and we lose like 70% of the number of eggs there. That’s another way I can protect them without hurting anything,” Rasmussen explains.
The invasive species extends much farther than just Swarthmore’s campus. Lanternflies could negatively impact tree nurseries and fruit trees, grapes, soybeans, and corn. In Berks County, the Pennsylvania origin of lanternflies, some vineyards have shut down. According to the Pennsylvania Department of Agriculture, an economic impact study estimated that lanternflies could cause a loss of $324 million annually and 1,800 jobs. Because of this, lanternflies are under quarantine in 34 counties in Pennsylvania to control the movement of items that are likely to be infested (Department of Agriculture). The poster shown is one displayed in the town of Swarthmore.
In an interview with The Phoenix, Abbey Peters ’26 recalled a similar quarantine in Delaware in 2019. Living close to the Delaware-Pennsylvania border, Peters and her mom had to bring papers in the car with them saying that they weren’t transporting lumber, as it could be carrying lanternflies. Before they left to go anywhere, they had to be very careful that they weren’t unknowingly carrying lanternflies.
“We also were never transporting anything that could have lanternflies on it. But yeah, my mom made sure before we left [that] there weren’t any caught on the tires or anything really,” she said.
While Peters and her mother’s actions may seem extra cautious, Rasmussen explained that it’s very necessary to stop lanternflies from spreading.
“[The spotted lanternfly] lays eggs everywhere. On cars, campers, rusty metal, it doesn’t really have a preference. So you’re very much encouraged if you have something like that and you’re going camping or hauling something from one place to another … you should check your vehicles,” he said.
The most important thing to do when you see a lanternfly is to kill it. Rasmussen recommends going at the fly from the front and stomping a few times to kill the fly. First-year Swarthmore students can also use the fly swatters they got at the beginning of the year. In addition, he recommends killing any egg masses, which will become a growing problem in the next few months.
It’s likely lanternflies won’t go away, and will be another invasive species, like the emerald ash borer or gypsy moth, that Swarthmore students will have to deal with in the years to come.
Very informative!