A tiny, wasp-like insect is making its way across North America, leaving a telltale trail of zigzag scars in elm leaves. The invasive elm zigzag sawfly, native to East Asia, is spreading quickly — and raising new concerns for elm trees from forests to city streets.

Researchers like Kelly Oten, an assistant professor and Extension specialist in the Department of Forestry and Environmental Resources at North Carolina State University, are studying the elm zigzag sawfly to help mitigate its impact on tree health.

Oten and a team of researchers from NC State and the U.S. Forest Service documented the elm zigzag sawfly’s rapid spread across North America in a 2025 paper published in the Journal of Integrated Pest Management.

Below, Oten provides an overview of the elm zigzag sawfly, including its appearance, life cycle, diet, signs and symptoms of infestation, impacts on tree health, geographic spread and timeline, factors contributing to its rapid expansion, and management strategies.

How to Identify the Elm Zigzag Sawfly 

Larva: The larva is a tiny, caterpillar-like insect that measures approximately 1.8 millimeters long. It is typically grayish-white to pale green, with dark bands across the head and distinctive T-shaped markings on the legs.

Adult: The adult is a small, shiny black, wasp-like insect measuring approximately 6–8 millimeters long. It has smoky-colored wings and pale legs. Despite its wasp-like appearance, it does not sting.

Life Cycle of the Elm Zigzag Sawfly

Reproduction: Elm zigzag sawflies reproduce primarily through parthenogenesis, with females laying eggs directly on elm leaves without mating. They can produce multiple generations per year, allowing populations to increase quickly during the growing season.

Life cycle: Female elm zigzag sawflies lay small eggs in elm leaves, where they hatch into larvae. Larvae feed, and after several stages of growth, mature larvae leave the tree and form cocoons. The larvae develop inside cocoons before emerging as adults.

Plants the Elm Zigzag Sawfly Feeds On

Elm trees: Elm zigzag sawfly larvae primarily feed on the leaves of elm trees, including American, Chinese, English, Siberian and winged elms, as well as several hybrid elm varieties.

Japanese zelkova: Recent research indicates that elm zigzag sawflies also feed on Japanese zelkova, an ornamental tree commonly planted in urban landscapes, along streets and in residential yards.

Signs of Elm Zigzag Sawfly Damage

Zigzag patterns: Elm zigzag sawfly larvae create distinctive zigzag patterns as they feed on the edges of elm leaves.

Heavy skeletonizing: As feeding continues, damaged leaves may develop brown or skeletonized areas where the larvae have consumed the leaf tissue.

Severe defoliation: Heavy infestations can cause significant leaf loss and premature defoliation, particularly when multiple generations feed on the same tree.

Effects of Infestation on Tree Health

Short-term impact: Heavy feeding can cause leaf damage and premature defoliation, reducing the tree’s ability to photosynthesize and produce energy.

Long-term impact: Repeated or severe defoliation can stress elm trees over time, potentially reducing growth and leaving already stressed or vulnerable trees more susceptible to other environmental pressures.

Elm Zigzag Sawfly Native Range and Habitat

East Asia: The elm zigzag sawfly is native to parts of eastern China, eastern Russia, Japan and the Korean Peninsula.

Habitat: In its native range, the elm zigzag sawfly is found in temperate deciduous forests and other areas where elm host trees grow.

Geographic Expansion and Timeline

Since it was initially detected outside its native range in the early 2000s, the elm zigzag sawfly has spread rapidly across North America, expanding its range into more than a dozen states across the U.S. and four Canadian provinces.

How the Elm Zigzag Sawfly Spreads

Natural dispersal: Adult elm zigzag sawflies naturally spread by flying between elm trees, covering an estimated 28 to 56 miles in one year. This allows established populations to gradually expand into nearby areas.

Human-assisted movement: Although elm zigzag sawflies can fly, human activity likely contributes to their rapid spread. Larvae form cocoons on objects such as twigs, leaves and vehicles, allowing the pest to hitchhike long distances. Sawfly cocoons have been found on truck wheel wells and side mirrors.

Plant transport: The sawfly may also spread through the movement of infested plants, although this pathway has not been confirmed as a significant source of spread. Because the insect overwinters in soil, cocoons could potentially be transported with potted plants and other nursery material.

Management Strategies

Inspect vehicles: Before traveling, check vehicle wheel wells, side mirrors and other surfaces for cocoons to help prevent accidental spread.

Monitor trees: Monitor elm trees for zigzag patterns on leaves, particularly in areas where the sawfly has been detected.

Dispose of infested material: Remove and properly dispose of heavily infested branches, larvae and cocoons. Avoid moving infested plant material to other locations.

Use insecticides: Insecticides labeled for sawfly control may help manage infestations. Follow all product directions and local regulations when applying treatments.

Encourage natural predators: Birds and parasitoid wasps may help suppress elm zigzag sawfly populations as part of an integrated pest management approach.

Report sightings: Report suspected infestations to local agricultural or environmental authorities. Early detection and reporting can help track the sawfly’s spread and support ongoing management efforts.

Stay informed: Check with local Extension services, agricultural agencies and environmental authorities for the latest guidance, management recommendations and information.