Spotted Lanternfly Egg Masses in Montgomery County: What to Do Before Spring

If you are seeing spotted lanternflies on your property this month, the useful thing to do is not to chase the adults around the yard. It is to find the egg masses they are laying right now and destroy them. Each mass holds roughly thirty to fifty eggs, it sits through the winter on bark, stone or anything else with a flat surface, and it hatches in spring. Scraping one off in the autumn removes next year’s population from your yard before it exists.

Montgomery County is now among the most heavily infested parts of Maryland, alongside Baltimore and the other central counties, and the county has been warning residents to expect the population to keep climbing over the next several years — with the northern end of the county, around Brookeville and Damascus, singled out. We are hearing about them on jobs from Rockville out to Olney.

Before any of that, though, the question almost everyone asks first.

Will spotted lanternflies kill my trees?

Almost certainly not, and this is worth saying plainly because most of what circulates online suggests otherwise.

The insect has been studied intensively since it reached Pennsylvania in 2014. In that time, researchers have recorded spotted lanternfly killing grapevines, tree of heaven, and black walnut saplings. Healthy, established ornamental and shade trees have not been recorded dying from spotted lanternfly feeding. Branch dieback and general decline have been observed on its favorite hosts — black walnut and maple in particular — but that is stress, not mortality.

So a mature oak, tulip poplar or red maple in a Bethesda or Kensington yard, covered in lanternflies in September, is being fed on rather than killed. That is genuinely different from the emerald ash borer, which does kill the ash trees it infests and which we remove the consequences of every week.

The exception is a tree that was already in trouble. Lanternfly feeding is one more demand on a tree that is also dealing with drought, root damage from construction, girdling roots or compacted soil. If a tree was declining before they arrived, they are not helping.

What they actually do to a Maryland yard

The damage is real, it is just not what people expect. Lanternflies feed on sap and excrete the excess as honeydew — a sugary liquid that rains down from wherever they are massed. Sooty mold then grows on it.

In practice that means a black film over whatever sits beneath the tree: decks, patio furniture, cars, play equipment, the hostas and azaleas underneath. On the tighter Chevy Chase and Silver Spring lots, where the outdoor living space is directly under a canopy, this is the complaint we hear rather than anything about the tree itself.

It also draws wasps and ants to the honeydew, and the adults swarm on trunks in numbers that a lot of people simply find unpleasant to walk past.

What to look for right now

The adults

About an inch long at rest, with grey forewings marked with black spots. The scarlet hindwings only show when they fly or startle, which is why people often describe seeing “a grey moth that flashes red”. They are poor fliers and tend to hop.

The egg masses — the ones that matter

These are easy to walk past. A fresh mass looks like a smear of wet putty or dried mud, roughly an inch to an inch and a half long, grey-brown, with a waxy coating over the top. As it ages the coating cracks and weathers away, and what is left looks like tidy rows of small brown seeds pressed into the surface.

The mistake is looking only at trees. Females lay on bark, but they will use almost any flat sheltered surface:

• Tree trunks and the underside of large limbs — smooth bark especially.
• Stone walls, retaining walls, brick, and the foundation of the house.
• Outdoor furniture, grills, the underside of tables and benches.
• Vehicles, trailers, boats, and anything parked under a tree — which is how they travel to new areas.
• Firewood stacks, fence rails, play equipment, and garden ornaments.

Check the sheltered side and the underside of things. That is where most of them are.

How to destroy an egg mass properly

It takes about ten seconds per mass and needs almost nothing:

1. Hold a bag or container of rubbing alcohol or hand sanitiser under the mass.
2. Scrape the mass off with an old card, a putty knife or a similar stiff edge, working from the edges so the whole thing comes away.
3. Let it fall straight into the alcohol, which kills the eggs.
4. Seal the container and bin it.

The part people get wrong is scraping the mass onto the ground and leaving it. Eggs on the ground can still hatch. It has to go into alcohol, or be crushed thoroughly.

You can keep doing this right through to spring — the masses are there all winter, and once the leaves are down they are much easier to spot. Earlier is better, but late is far better than not at all.

The tree that turns your property into a nursery

If you have tree of heaven on your land, it is doing more to sustain the local lanternfly population than anything else in your yard.

Ailanthus altissima is an invasive weed tree, common on field edges, fence lines, alley margins and anywhere the ground has been disturbed. It is the insect’s preferred host, and lanternflies concentrate on it heavily. Removing it takes away the anchor.

It is recognizable by long compound leaves with many leaflets, each with a small notch and gland near its base, and by a strong unpleasant smell when a leaf or twig is crushed — which is where the nickname “stink tree” comes from. It grows very fast and often comes up in clumps.

Cutting it down on its own does not work, and usually makes it worse: it responds by sending up dozens of root suckers across a wider area. The root system has to be treated, which is what separates removing it from simply mowing it. This is the one piece of lanternfly work where hiring someone genuinely changes the outcome, and it is the same argument as taking out a Norway maple — an invasive tree doing steady damage that is easy to ignore.

What is not worth doing

A fair amount of effort gets wasted on this insect every autumn.

• Blanket-spraying the yard. It does not meaningfully reduce a population that flies in from elsewhere, and it kills pollinators and the predators that do help.
• Home remedies — dish soap, vinegar and similar mixtures. These scorch foliage and damage plants, and Extension services advise against them.
• Plain sticky bands on trunks. They catch birds, squirrels and bats. If a band is used at all it needs a wire cage or guard over it.
• Worrying about individual adults on a healthy tree. Squash them if you like; it will not change the population, and the tree is not in danger.

The two things that do move the needle are destroying egg masses and getting rid of tree of heaven.

When it is worth calling an arborist

Most of this is a homeowner job. It is worth a professional call in four situations:

• There is tree of heaven on the property and you want it gone properly rather than resprouting wider next year.
• A tree was already declining — thinning canopy, dieback, poor color — before the lanternflies arrived, and you want to know what is actually wrong with it.
• Honeydew and sooty mold are coating a deck, patio or driveway and you want to know which tree is producing it and whether pruning would help.
• A tree of heaven is growing against the house, a wall or a utility line, where taking it down is a structural job rather than a weekend one.

For the second of those, an assessment of the tree’s condition is a different piece of work from an estimate, and it is what tells you whether the tree is worth treating or whether the lanternflies are a symptom of something further along.

Send us the tree

Seeing lanternflies or egg masses on your property? Send Rock Creek photographs of the tree and of anything you have found on the trunk or nearby surfaces. Our arborists can identify whether you are dealing with tree of heaven, tell you whether the tree they are feeding on is actually at risk, and give you a written estimate for removal or treatment. Free estimates across Rockville, Bethesda, Potomac, Silver Spring, Chevy Chase, Kensington, Gaithersburg and Montgomery County.

Maryland’s guidance on the insect, including how it is being tracked across the state, is published by the Maryland Department of Agriculture, and the University of Maryland Extension keeps a home-garden guide that is the best plain-language reference available.