That sticky, shiny coating on your car, patio, or deck chairs isn’t actually poop in the traditional sense. Spotted lanternflies excrete a sugary liquid waste called honeydew, and when these insects gather in large numbers, it can rain down heavily enough to coat everything beneath them. It’s essentially undigested plant sugar, and it creates a cascade of problems from black mold growth to swarms of wasps.
What Honeydew Actually Is
Spotted lanternflies feed by piercing into trees and other plants with needle-like mouthparts and sucking out the sap. They’re after nitrogen and amino acids, but plant sap is mostly sugar water. Because they can’t fully digest all that sugar, they excrete the excess as a liquid waste. This honeydew drips continuously while the insects feed, and it can pool on any surface below: leaves, sidewalks, cars, outdoor furniture, playsets.
The volume can be staggering. Spotted lanternflies are swarm feeders. Researchers have documented up to 400 adults on a single grapevine, and each one is constantly cycling sap through its body and dripping honeydew. If you’ve walked under an infested tree and felt what seemed like light rain on a clear day, that was lanternfly honeydew falling from above.
The Black Mold That Follows
Honeydew by itself is sticky and annoying, but the real damage comes next. Left to accumulate outdoors, honeydew acts as a growth medium for sooty mold fungi. This is the dark, sometimes black coating you’ll see on leaves, branches, railings, and pavement beneath infested trees. It looks alarming, almost like the surface has been lightly charred.
On plants, sooty mold blocks sunlight and reduces the leaves’ ability to photosynthesize. For homeowners, the combination of sticky honeydew and dark mold can make outdoor spaces unusable during peak lanternfly season, typically late summer through fall when adults are most active.
It Attracts Wasps, Bees, and Ants
Because honeydew is essentially sugar water, it draws every sugar-seeking insect in the area. Yellowjackets, wasps, hornets, and ants all show up to feed on the sticky residue. If you’ve noticed more stinging insects around your yard during lanternfly season, the honeydew is likely the reason. This secondary pest problem can make outdoor dining or yard work genuinely hazardous for people with sting allergies.
Honeybees collect lanternfly honeydew too. They process it into a distinct type of honey that starts appearing in hives around August, when adult lanternflies emerge in large numbers. This honeydew honey is dark brown with a smoky odor, less sweet than typical honey, and leaves a lingering aftertaste. Opinions on the flavor are split. In informal taste tests, roughly half of people enjoy it. Bakeries purchase it, and some beekeepers market it as a novelty product. Lab testing shows pesticide levels in honeydew honey from treated areas are far below any safety concern, and the honey is safe for both humans and bees.
Which Plants Get Hit Hardest
Spotted lanternflies feed on more than 70 plant species, but grapes take the worst damage. Heavy feeding weakens vines so severely that they lose winter hardiness, fail to bloom the following season, and can die outright. This makes lanternflies a serious threat to vineyards across the mid-Atlantic and anywhere the insect continues to spread.
In yards and natural areas, tree of heaven is their preferred host, but they also target black walnut, silver and red maples, willow, river birch, black cherry, and tulip poplar. Silver maples seem to be a particular favorite among the maples. If you have any of these trees and you’re finding honeydew on surfaces below, the lanternflies are likely feeding overhead even if you haven’t spotted them yet.
Cleaning Honeydew Off Surfaces
Fresh honeydew washes off relatively easily with warm soapy water and a sponge or cloth. The sooner you get to it, the better. Once it dries and sooty mold starts growing, removal takes more effort. For cars, a standard car wash with soap and water works if you don’t let it sit for weeks. For decks and pavers, a pressure washer on a moderate setting can clear both the honeydew residue and the mold layer.
On plants, there’s not much you can do about sooty mold other than managing the lanternfly population itself. The mold won’t kill a healthy, mature tree on its own, but it adds stress on top of the sap loss from feeding. Younger or already-stressed trees are more vulnerable. Removing tree of heaven from your property can reduce the number of lanternflies that congregate in your yard, since it’s their preferred host for both feeding and egg-laying.
Is It Harmful to Pets?
Honeydew itself is sugar water and not toxic. Dogs or cats that walk through it or lick it off their paws are not in danger from the honeydew alone. The bigger concern is if your yard has been treated with insecticides targeting lanternflies. In that case, follow the product’s safety guidelines for keeping pets off treated surfaces for the recommended period. The honeydew and sooty mold, while unpleasant, are not known to pose a poisoning risk to domestic animals.