New York State is dealing with several destructive invasive insects that threaten forests, shade trees, and agriculture. The most damaging include the emerald ash borer, spotted lanternfly, hemlock woolly adelgid, spongy moth, and a newer arrival called the elm zigzag sawfly. Here’s what each one does, how to spot it, and what you can do.
Emerald Ash Borer
The emerald ash borer is the most destructive invasive insect in New York’s forests. This metallic green beetle, originally from Asia, has been confirmed in every New York county except Hamilton and Lewis since it was first detected in the state in 2009. It has killed millions of ash trees across North America and caused billions of dollars in damage.
All three of New York’s native ash species (white, green, and black) are at risk. After the adult beetles lay eggs on bark, the larvae chew inward and feed on the living tissue between the bark and sapwood, carving out distinctive S-shaped tunnels. This cuts off the tree’s ability to move water and nutrients. Once infested, most ash trees die within two to four years.
Signs of an infestation include woodpecker damage that strips away dark outer bark (called “blonding”), canopy dieback, yellowing or browning leaves, D-shaped exit holes in the bark, and S-shaped galleries visible where bark has split or fallen off. New York is no longer actively managing individual infestations, but the beetle is classified as a prohibited invasive species, meaning it’s illegal to knowingly transport it.
Spotted Lanternfly
The spotted lanternfly is the invasive insect New Yorkers are most likely to encounter in everyday life, especially in the Hudson Valley and New York City metro area. Adults are about an inch long with gray forewings dotted in black spots and vivid red hindwings. They feed by piercing plant tissue and sucking sap from grapevines, fruit trees, hops, maples, and many ornamental plants.
The damage is twofold: heavy feeding weakens and can kill host plants, and the insects excrete a sticky substance called honeydew that coats surfaces below and promotes black sooty mold growth. Vineyards and orchards face particular economic risk. Spotted lanternflies also lay egg masses on almost any flat outdoor surface, from tree trunks to patio furniture to car bumpers, which is one way they spread so quickly.
If you find spotted lanternflies or their egg masses, the state asks you to photograph them with something for scale (a coin or ruler works) and report the sighting through iMapInvasives. Scraping and destroying egg masses over the winter months is one of the simplest things residents can do to slow the spread. The egg masses look like smears of dried mud, roughly an inch long, often found on tree bark, stone, or metal surfaces.
Hemlock Woolly Adelgid
The hemlock woolly adelgid is a tiny, aphid-like insect from Asia that targets eastern hemlock, the most common hemlock species in New York. It attaches at the base of needles and feeds on the tree’s stored starches, disrupting nutrient flow to twigs and needles. Infested hemlocks typically die within 4 to 10 years.
The easiest way to identify an infestation is to look at the undersides of hemlock branches near the base of the needles. Small white woolly masses, each about a quarter the size of a cotton swab, are the insect’s egg sacs. Other signs include needle loss, branch dieback, and a grayish tint to the remaining needles.
Losing hemlocks would reshape New York’s ecosystems in significant ways. Hemlock stands create cool, dark, sheltered environments that moose, black bears, salamanders, and migrating birds depend on. Hemlocks grow on steep slopes where few other trees can, stabilizing shallow soils and preventing erosion. Along streams, their shade keeps water temperatures low enough for cold-water fish like trout. Removing them from the landscape doesn’t just mean losing a tree species; it means losing the habitat that dozens of other species rely on.
Elm Zigzag Sawfly
New York’s newest invasive insect pest is the elm zigzag sawfly, first detected in St. Lawrence County in August 2022. By summer 2023, it had been confirmed in counties across the state, from Allegany and Ontario in the west to Clinton County near the Canadian border, with new counties being added weekly. It feeds exclusively on elm leaves.
You can identify its presence by the distinctive zigzag pattern it chews into leaves. So far, most reported damage has been minor, with only 2 to 5 percent of leaves showing feeding marks. But at least one homeowner in Niskayuna reported several Siberian elms in their yard that were severely defoliated. Because the sawfly is so new to the region, researchers at SUNY College of Environmental Science and Forestry are still studying how much damage it could ultimately cause.
The state is actively asking residents to watch for zigzag feeding patterns on elm leaves and report sightings through iMapInvasives. Early detection reports are especially valuable for a newly arrived species because they help map how far and fast it’s spreading.
How These Pests Spread
Firewood is one of the biggest vectors for moving invasive insects into new areas. Beetle larvae and egg masses hiding in or on cut wood can hitch a ride hundreds of miles in the back of a truck. New York has a regulation restricting the movement of firewood of any species to within 50 miles of its source or origin. If you’re heading to a campground or cabin, buy firewood locally rather than bringing it from home.
Spotted lanternflies spread partly through egg masses laid on vehicles, outdoor equipment, and shipping materials. Checking your car, trailer, or any items stored outside before traveling from an infested area is a practical step that slows their advance.
How to Report Sightings
New York uses iMapInvasives as its central reporting platform for invasive species sightings. To submit a useful report, photograph the insect, any egg masses, or signs of damage with a coin or ruler in the frame for scale. Spotted lanternfly sightings can also be reported through the state’s AGM (Agriculture and Markets) webpage. These reports directly inform where the state focuses monitoring and research, so even a single photo from a new location matters.