Spotted lanternflies damage trees by piercing the bark and draining sugary sap from the phloem, the tissue that transports nutrients throughout the plant. In most cases, they don’t kill mature trees outright. Instead, they weaken them over time by depleting energy reserves and creating conditions for secondary damage like mold growth. The plants confirmed to die from lanternfly feeding are grapevines, tree of heaven, and black walnut saplings.
How Lanternflies Feed
Spotted lanternflies belong to a group of insects with piercing-sucking mouthparts, essentially a needle-like beak that drills into a plant’s phloem to tap directly into the sugary sap flowing inside. They’re after the nitrogen and amino acids dissolved in that sap, but those nutrients make up only a small fraction of the liquid. To get enough, the insects consume massive quantities of sap and excrete the excess sugar-water as a sticky substance called honeydew.
Interestingly, lanternflies don’t have strong muscles for pumping sap out of a plant. They rely on the plant’s own internal pressure to push sap into their mouthparts. This is why they prefer vigorous, well-hydrated plants with strong sap flow. Early-stage nymphs have weaker beaks and can only feed on soft, new growth or non-woody plants. By the fourth nymph stage and into adulthood, their mouthparts are strong enough to penetrate tree bark, older wood, and the trunks of established plants.
Energy Drain and Carbohydrate Loss
The core damage mechanism is energy theft. Trees produce sugars through photosynthesis and store carbohydrates to fuel growth, fight disease, and survive winter. When large groups of lanternflies feed on a tree, they siphon off those sugars faster than the tree can replace them. Research from Penn State has shown that heavy feeding alters the sugar and carbohydrate chemistry inside host plants, though different tree species respond differently.
This drain on stored energy has several downstream effects. Photosynthesis slows. Nutrient levels drop. The tree becomes less cold-hardy, meaning it’s more vulnerable to winter damage it would normally survive. Over time, branches may wilt, leaves may drop prematurely, and sections of the canopy can die back. None of this necessarily kills a large, healthy tree in a single season, but it compounds year after year, leaving the tree progressively weaker and more susceptible to other stressors like drought, disease, or additional pest pressure.
Honeydew and Sooty Mold
The honeydew lanternflies excrete creates a second layer of damage. When swarms feed on a tree, the sticky waste coats the bark, lower branches, leaves, and everything beneath the canopy. Left to accumulate, honeydew becomes a growth medium for dark fungi collectively called sooty mold.
Sooty mold doesn’t infect the tree directly, but it coats leaf surfaces in a thin, dark film that blocks sunlight. Since leaves need sunlight to photosynthesize, a heavy coating of sooty mold reduces the tree’s ability to produce energy at the same time the insects are draining its reserves. It’s a one-two punch: less energy coming in, more energy going out. The honeydew also ferments and produces a noticeable odor that attracts bees, wasps, and other insects to the area.
What Tree Damage Looks Like
If lanternflies are feeding on a tree, the earliest visible sign is often sap oozing or weeping from small puncture wounds on the trunk. These wet spots may give off a fermented smell. Below the feeding sites, you’ll likely notice a buildup of sticky honeydew on the ground, on outdoor furniture, on cars parked nearby, and potentially dark patches of sooty mold on surfaces that stay wet.
As feeding pressure continues, the tree itself may show wilting leaves, premature leaf drop, and branch dieback, where individual limbs stop producing new growth and die. In severe infestations, the overall canopy thins out and the tree takes on a visibly stressed appearance.
Which Plants Actually Die
Despite the alarming swarms, spotted lanternflies are not confirmed to kill most established trees. Penn State’s research identifies only three plants known to die from feeding: grapevines, tree of heaven, and black walnut saplings. For everything else, lanternfly feeding is classified as a plant stressor that contributes to long-term weakening rather than direct mortality.
Grapevines are by far the most vulnerable. Up to 400 adult lanternflies have been documented on a single vine. That kind of feeding pressure can reduce or completely eliminate production, and in the worst cases, it kills the vine. Pennsylvania vineyards experienced significant losses in the early years of infestation there, with some operations forced to replant entirely. Economic modeling for New York State estimates potential grape production losses reaching $8.8 million per year once infestations become established.
For shade trees and hardwoods, the situation is less about sudden death and more about a slow decline. A mature maple or oak can withstand a season of heavy feeding, but repeated years of sap loss, reduced photosynthesis, and depleted carbohydrate stores weaken it to the point where a harsh winter, a drought, or a secondary pest could finish it off. The lanternfly feeding alone may not deliver the killing blow, but it sets the stage for it.
Why Large Swarms Matter
A handful of lanternflies on a large tree won’t cause meaningful harm. The damage becomes serious when the insects aggregate in large numbers, which is their natural tendency. Spotted lanternflies are social feeders that congregate in dense groups on preferred hosts, and because they rely on the plant’s sap pressure rather than their own pumping strength, a well-hydrated, vigorous tree is actually more attractive to them than a struggling one.
This clustering behavior means damage is often concentrated on specific trees rather than spread evenly across a landscape. A single tree in a yard or park can become heavily infested while nearby trees of different species remain relatively untouched. The concentrated feeding, combined with the honeydew buildup and sooty mold beneath the swarm, can make the damage look catastrophic even when the tree has a reasonable chance of recovery if the pest pressure is reduced.