The sticky mess is honeydew, the sugary waste these bugs push out while they feed on sap. Spotted lanternfly honeydew drips off the branches and coats whatever you keep under the tree, and you end up with a tacky film that never quite dries. USDA APHIS lays out the rest of the chain, from the vinegar-like smell that shows up as the sugar ferments to the black growth you find on top.
My back kitchen window went cloudy first. A gray haze on the glass that a normal wipe would not touch, then a sour vinegar smell every time I cracked the sash open in the afternoon. I scraped a fingernail down the pane and got a gummy line. The maple outside had adults packed along the trunk, and every plant under that tree had gone black on top.
Sap feeding starts all of the trouble. These bugs work stems, leaves and bark with piercing-sucking mouthparts, and fruit is not on the menu. That feeding makes honeydew, a sticky sugary excretion, and the drops land on whatever sits below you. You rarely see the mist land. You will spot the shine on a car hood long before you spot the insects overhead.
The black film is sooty mold, and the mold grows on the sugar rather than inside the tree. Spores land on the honeydew, feed on the sugar, and spread into a dark crust across leaves, bark, your deck rails and your siding. Your tree is not sick with a fungus, so treating the tree does nothing about the film. Under the heaviest feeding the groundcover below dies off, killed by mold on the sugar that rained down.
The smell is the part you notice next. Honeydew ferments where it lands, and under a heavily fed tree you get a wet, vinegary odor you can catch from across the yard. Sap weeping from wounds on the trunk adds to that sour edge. Other insects come for the sugar too, so you also get a busy crowd on the trunk that has nothing to do with the lanternflies.
Your car takes the worst of it if you park under the canopy, because the hood collects the drip and bakes the sugar on by noon. Patio furniture, grills and trash can lids pick up the same coating. That nuisance is the main household harm you get from spotted lanternfly honeydew. The bugs pile up on trees and on the surfaces of the synthetic things you leave outside.
Cleanup goes far easier the sooner you get to the job. Fresh honeydew rinses off with soap and water, but once sooty mold sets into a crust you are into real scrubbing. Sticky residue on deck boards is the complaint I hear most, and your boards turn gray and slippery underfoot if you leave the film through a wet week. Give the deck a rinse after a heavy week of drip, and you save yourself an afternoon with a stiff brush later.
Hose the surface down before the honeydew dries on you. Wet sugar comes off with a fraction of the work.
Go over your deck, rails and furniture with warm soapy water and a stiff brush to lift what the hose leaves behind.
Park outside the drip line, and pull your cushions and grill out from under the canopy while feeding is heavy.
Look at the groundcover under your tree, because that is where the mold does harm rather than make a mess.
Adults on your siding look alarming and cause no structural damage. The bugs land on buildings for warmth or height, and nobody has pinned down every other reason. Your walls are not food, and nothing is boring into the wood. The mess on that wall came off the tree above. A wash takes care of your siding, and the feeding overhead is the part that deserves your attention.
Read the full article: Spotted Lanternfly: What It Actually Damages
