Spotted Lanternfly in Your Garden: What It Actually Harms

How to know it’s spotted lanternfly

Only the adult has wings, and even the adult usually keeps the showy ones hidden — which is why this insect is easy to miss until there are many of them.

Egg mass:

A flat patch covered with a gray-brown, mud-like coating, laid on tree trunks, decks, houses, outdoor equipment and rocks. Each mass holds about 35 eggs on average.

Early nymphs:

The first three stages are black with bright white spots, starting around an eighth of an inch and roughly doubling in size at each molt.

Late nymph:

The fourth stage is unmistakable — red with white dots and black stripes, about a half-inch long.

Adult:

About an inch long, with a black abdomen banded in yellow, gray forewings marked with black spots, and hindwings patched with red, black and white. At rest the forewings cover everything else and read as tree bark.

Behavior:

Both nymphs and adults are strong jumpers and will jump when approached or prodded — a useful tell at a distance.

The year it runs on

Generations: One generation a year.

Where it spends the winter: As eggs, in those mud-coated masses on any hard surface outdoors — which is exactly why the insect travels on vehicles, firewood and outdoor furniture.

1. September to December: Eggs are laid on trees, decks, houses, equipment and rocks.
2. Late April to June: Eggs hatch. Nymphs feed on sap from tender new growth, are in near-constant motion, and move through plants in groups.
3. July onward: Adults emerge and shift to feeding on the twigs, branches and trunks of woody plants.
4. Fall, until hard freezes: Adults stay active and gather in large numbers on favored trees before being killed by hard freezes.

This calendar is Pennsylvania’s, from Penn State Extension, where the insect was first established in the United States. Because spotted lanternfly spreads largely by hitchhiking rather than by flying, whether it is on your land is a question about quarantines and movement, not about your latitude — which is what the rest of this playbook is about.

What the damage actually costs you

This is a sap feeder, so the damage is stress and honeydew rather than chewed leaves — and it falls very unevenly across plants.

• •Large numbers of insects gathered on trunks and branches, often returning year after year to the same "hot" tree even when neighboring trees look identical.
• •Dieback of individual tree branches where large numbers of nymphs have fed.
• •Damage to perennials and annuals where nymph numbers are high.

How much the plant can take: It depends entirely on the plant. Penn State reports that heavy feeding has contributed to the death of grapevines, tree-of-heaven and black walnut saplings, and that high feeding levels may stress trees by reducing photosynthesis — with damage more apparent on plants already stressed by something else. Nymphs take less sap than adults, so the same number of nymphs does less harm. For most garden plants the honest answer is that the insect is a nuisance and a quarantine problem rather than a threat to the plant.

The move

Penn State Extension’s own first instruction is to “avoid overreacting to the situation and teach others not to overreact.” These are the moves that earn their keep, from their Spotted Lanternfly Management Guide:

1. 1

   Scrape the egg masses you can reach

   Eggs are laid September through December under a mud-like covering — roughly 35 per mass — and sit there until they hatch from late April into June. For any mass within reach, Penn State found that scraping or smashing works better than the oil sprays sold as ovicides.

2. 2

   Scout before you treat anything

   Penn State emphasizes that not every tree in an already-infested area needs to be treated: a few lanternflies on a large, healthy tree are unlikely to do permanent damage. Scout your own property through the season, then treat only where high populations show up and persist.

3. 3

   If you trap, use a circle trap — and screen any sticky band

   A circle trap is a modified funnel you can buy or build, set about four feet up a smooth-barked trunk; it catches the most from hatch through June. Plain sticky bands are not recommended without a wildlife barrier — they catch bats, squirrels, small birds, lizards and beneficial insects. If you use one, guard it with mesh window screening; chicken wire is too open to help.

4. 4

   Never spray a plant that is blooming

   To protect the pollinators that visit flowers for nectar, no insecticide should go on a plant in bloom. Penn State also notes that killing the lanternflies present today will not stop more from arriving later in the season.

5. 5

   Check the car, the firewood, the patio furniture

   The quarantines exist to stop human-assisted spread: adults can hold onto a vehicle at 65 mph, and egg masses hide in wheel wells and on outdoor gear. The permit requirement applies to businesses, not households — what residents are asked to do is inspect belongings before travelling out of a quarantined county, and report a sighting in a new area to 1-888-4BAD-FLY.

Sources: Penn State Extension (2024). Spotted Lanternfly Management Guide; Penn State Extension (2021). How You Can Comply with the Spotted Lanternfly Quarantine Regulations

The plants in this playbook