Spotted lanternfly nymphs are hatching right now across Bucks County. If you’ve been seeing tiny black bugs with white dots crawling up your trees and fences in May, that’s them. They won’t kill most healthy established trees outright — but they will stress them significantly, excrete sticky honeydew that grows into black sooty mold, and if your trees are already dealing with Emerald Ash Borer or drought stress, the combination can be serious. Here’s what you need to know at every stage of the year.
What Are Spotted Lanternflies and Why Are They in Bucks County?
The spotted lanternfly (Lycorma delicatula) is an invasive planthopper native to China, India, and Vietnam. It arrived in the United States in 2014 when an egg mass hitchhiked into Berks County, Pennsylvania on imported stone. From there it spread rapidly across eastern Pennsylvania — and Bucks County has been in the established infestation zone since the early years of the outbreak.
SLF is not a true fly despite the name. It’s a planthopper — an insect that feeds by piercing plant tissue and sucking sap. It doesn’t bite, doesn’t sting, and poses no direct threat to humans or pets. The damage is entirely to plants: trees, vines, crops, and ornamentals. Pennsylvania alone has estimated hundreds of millions of dollars in potential annual agricultural impact if the population isn’t managed.
In Bucks County specifically, SLF has been present long enough that most homeowners will encounter it every season. The question isn’t whether you’ll see them — it’s what to do when you do.
When Do Spotted Lanternflies Hatch in Pennsylvania?
The SLF calendar runs year-round in Pennsylvania, with four distinct stages that each require a different response. The timing below reflects the Bucks County climate — slightly warmer than central PA, so expect the earlier end of these windows in areas like Warminster, Doylestown, and Perkasie.
-
OCT
–JUNOverwinterEgg Mass StageAfter mating in fall, adult females lay egg masses on any hard, smooth surface — tree bark, fence posts, outdoor furniture, rock walls, vehicle undercarriages. Each mass contains 30–50 eggs and is covered in a gray, waxy coating that looks like dried mud or putty smeared across the surface, about 1–1.5 inches long. Egg masses overwinter and begin hatching in late April when temperatures consistently reach the mid-50s. You can find and destroy them any time between October and early June — every egg mass you scrape is 30–50 fewer nymphs in the summer.
What to do: Scrape egg masses into a zip-lock bag with rubbing alcohol or hand sanitizer. Seal it and throw it away. Don’t just scrape onto the ground — eggs can still hatch. -
MAY
–JULNymphsEarly Nymph Stage (1st–3rd Instar)This is where Bucks County is right now in mid-May. First through third instar nymphs are small — anywhere from ⅛ to ½ inch — and jet black with bright white spots arranged in rows. They’re fast, jumpy, and tend to congregate on smooth-barked trees and shrubs. At this stage they’re feeding actively but are easiest to kill because of their small size and vulnerability. You’ll often see them on Tree of Heaven first, then spreading to nearby oaks, maples, and other host trees. They’re hard to miss once you know what you’re looking for — that black-and-white polka dot pattern is distinctive.
What to do: Stomp them on sight. Use circle traps or covered sticky bands on host trees (see FAQ on wildlife-safe banding). Insecticidal soap sprays work at this stage. Kill every one you see — population pressure matters. -
JUL
–AUGLate NymphsLate Nymph Stage (4th Instar)Fourth instar nymphs are hard to miss: they turn bright red with white spots and black stripes, and grow to about ¾ inch. This is the stage that gets the most attention because the color is striking. They’re still nymphs — no wings yet — but they’re feeding heavily and can aggregate in large numbers on the same tree. Honeydew excretion increases significantly at this stage, and if you have a heavily infested tree you’ll often notice a sweet, fermented smell and see bees and wasps attracted to the sticky residue. Sooty mold begins appearing on bark around this time.
What to do: Same as early nymphs — stomp, trap, and spray. Contact insecticides are effective at this stage. Watch for sooty mold beginning to develop on heavily infested trees. -
AUG
–NOVAdultsAdult StageAdults emerge in late July and August, reaching full size at about an inch long. At rest they look like a grayish-tan moth with black spots. When they open their wings you’ll see the brilliant red hindwings — a warning display. Adults can fly, which makes population management harder. They tend to aggregate in enormous numbers in September and October, covering tree trunks and fences in clusters that can number in the hundreds on a single tree. Adults feed heavily to build energy reserves for egg-laying, which happens from September through November. After first frost, adults die off — but the eggs they laid will overwinter and start the cycle again.
What to do: Contact insecticides, circle traps, stomp on sight. Focus on removing Tree of Heaven from your property to eliminate the primary host. Check vehicles and outdoor items before moving them out of quarantine areas.
What Do Spotted Lanternflies Actually Do to Your Trees?
SLF feeds by inserting needle-like mouthparts into the phloem — the layer of tissue just beneath the bark that carries sugars produced by photosynthesis throughout the tree. This feeding draws resources away from the tree and, when infestations are heavy, can significantly weaken the tree’s ability to grow, repair damage, and fight off other threats.
The immediate damage from feeding is stress: reduced energy reserves, weakened immune response, and increased vulnerability to secondary pests and disease. But the secondary effects are often more visible and more alarming to homeowners.
Honeydew
As SLF feeds, it excretes a sugary liquid called honeydew. On a heavily infested tree, this substance drips from the canopy and coats everything below — bark, lower branches, patio furniture, cars, fences, and the ground around the tree. If you notice a sticky film on surfaces near your trees in summer, that’s almost certainly honeydew. It attracts bees, wasps, and ants, and creates the conditions for the bigger secondary problem.
Sooty Mold
Honeydew is the perfect growth medium for sooty mold — a collective term for several species of black fungi that colonize the sticky coating left behind by SLF. Sooty mold doesn’t infect the tree itself, but it coats bark and leaves with a dark, powdery layer that blocks sunlight and reduces photosynthesis. On a tree dealing with heavy infestation season after season, the cumulative effect is meaningful. If you see what looks like black paint or soot on your tree trunks, that’s sooty mold from an SLF infestation — often a current or recent one.
A tree already stressed by Emerald Ash Borer, drought, root damage, or disease is significantly more vulnerable to SLF than a healthy tree. If you have ash trees with EAB and they’re also dealing with heavy SLF feeding, that combination can accelerate decline considerably. Call us if you’re seeing signs of both — those trees need to be assessed sooner rather than later.