Elms are a well-known tree species loved for their elegant shape and green leaves that turn gold in the fall. Unfortunately, these trees are also susceptible to damage from the invasive elm zigzag sawfly.
The elm zigzag sawfly is native to eastern Asia and was found in Illinois in 2024. It can defoliate elm trees and related species, affecting your tree’s health.
This insect has been spotted in the Chicago region. While most trees can recover from infestation, weakened, stressed trees with repeated defoliation are at risk. Knowing what a zigzag sawfly looks like, symptoms of zigzag sawfly damage, and how to treat the invasive pest can help ensure the elm trees in your backyard maintain their elegance.
Life Cycle of Zigzag Sawfly
Elm zigzag sawfly larvae cause the most damage to a tree when they feed in early May and throughout the summer. During the larval stage, zigzag sawflies are tiny, green caterpillar-looking insects. The pupae can sometimes be found with a lattice-like cocoon on the underside of the tree’s leaves.
In adulthood, zigzag sawflies are 6-7 millimeters long, black, and wasp-like with a white patch on the bottom of the thorax, yellow legs ending in white tarsi, and smoky brown wings. It’s more common to spot larvae than adults.
As the name suggests, elm zigzag sawflies prefer elm trees, specifically Siberian elms (Ulmus pumila) and American elms (U. americana). Trees resistant to Dutch Elm disease are also susceptible.
Symptoms of Elm Zigzag Sawfly
If you suspect a zigzag sawfly infestation, look out for these symptoms:
● Small, zigzag chewing patterns on leaves
● Tiny green caterpillar-looking insects
● Lattice-like cocoons on leaves
If you’re unsure whether you have an elm tree on your property, look for a large, deciduous tree with distinguished, rough, grooved bark and pointed, oval leaves with saw-toothed edges.
Elm Zigzag Sawfly Management & Treatment
Elm zigzag sawfly management includes early detection, monitoring, and cultural care. While zigzag sawfly damage looks severe, a mature and healthy tree can recover from periodic defoliation. Watering, mulch, compost, and other soil care practices can help if you're concerned about your tree's health.
An arborist may prescribe contact insecticides for severe sawfly populations. But be careful, as sawflies can quickly re-invade a treated area.
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