Elm Zigzag Sawfly

Aproceros leucopoda

Images of this species:

Common look-alikes:


Elm zigzag sawfly (EZS), once hatched, has three life stages: larva, pupa and adult fly.

Larvae are very small, 1.8 mm long and a grayish-white color after first emerging from the egg. Mature larvae are green with a black band on their head and T-shaped brown or black markings above the second and third pair of true legs. They can grow up to 10-11 mm long.

The lattice-like, silken cocoons are attached to undersides of leaves, branches, or shoots. In summer, the cocoon is loosely woven and light; overwintering cocoons are dense and found in the decomposing organic material layer (duff) on the ground. During the winter months, the dormant pupae often go unnoticed, buried just beneath the duff and leaf litter. Although an isolated pupa would be difficult, if not almost impossible, to identify as an elm zigzag sawfly pupa. A pupa within a lattice-like cocoon on the underside of an elm leaf is likely EZS.

Adult elm zigzag sawfly are small, shiny black, winged insects, reaching 7-8 mm long. There is a white patch on the underside of the thorax and a dark brown “upper lip". They have yellow to white legs with white tips and smoky-brown wings.


The signature ‘zigzag’ pattern is key to identifying this species in the early stages of the larval form. Larvae can be found during the months of May through October, and though EZS are small insects, outbreaks can defoliate large elm trees. Elm zigzag sawfly can go unnoticed for a long period of time after introduction because early infestations are often difficult to detect as defoliation is less noticeable in low densities.

Young elm zigzag sawfly larvae create a characteristic (and namesake) zigzag pattern in leaves, while older larvae feed more broadly on leaf tissue, leaving behind only thick leaf veins and often eliminating the zigzag-shaped damage.

Generally, defoliated trees can recover from a defoliation event. However, if trees are heavily defoliated year after year, they may become weakened or stressed, which predisposes them to other pests or results in tree death.



Elm zigzag sawfly is native to East Asia, including Japan, eastern Russia, eastern China, and the Korean peninsula. It was first detected in Europe, where it is considered invasive, in 2003. It was first detected in North America in Québec, Canada in 2020 and has since been found in numerous states in the US including Virginia (2021) and North Carolina, Maryland, Pennsylvania, and New York in 2022.

Host Species

In Europe, the insect attacks almost all elm species (Ulmus sp.), both native and exotic, including elm cultivars resistant to Dutch elm disease. During the first year of its discovery in Canada (2020), it was found mainly on American elm (Ulmus americana), but all elm species planted in North America should be considered as potential hosts.

Life Cycle

Adults reproduce parthenogenetically, meaning females reproduce without mating. No male elm zigzag sawflies have been observed.

Females lay up to 60 eggs singly along the tips of elm leaf serrations. Within eight days, larvae emerge and begin feeding. Elm zigzag sawfly larvae have six instars and pupate within three weeks of emerging from the egg. Two types of cocoons may be formed: either a loosely-spun, net-like cocoon attached to leaves (created during summer months) or a solid-walled cocoon in leaf litter or soil (overwintering generation).

In North Carolina, where heavy defoliation was observed in mid-August (2022), the net-like cocoons were attached to other objects (e.g., fence posts) in the absence of leaves, which had been consumed. Adults emerge within 10 days of cocoon creation. Research in Europe, upon which these life stage estimates are based, indicates a full generation can occur in less than a month (24-29 days).

Multiple generations of elm zigzag sawfly can occur per year, but the number varies. For example, in Virginia, two generations were observed in 2021 and one generation in 2022. Lab-reared elm zigzag sawfly have up to seven generations per year, but field observations in Europe and Russia indicate up to four generations occur per year.

Ecological Threat

Elm zigzag sawfly is a proven highly competitive elm specialist which could impact native elm browsers. North America is home to its own native elm feeding insects which could be outcompeted by elm zigzag sawfly. Significant branch die-back caused by the pest can contribute to weakened overall tree health, and potentially tree mortality. This has potential to further exacerbate the decline of elm trees in conjunction with other pressures including Dutch elm disease (Ophiostoma ulmi).

Management Options

As a new invasive species, little is known about effective management for elm zigzag sawfly. Small populations can be removed by hand. For heavy infestations or large trees, a general-purpose insecticide labeled for use on trees and shrubs can be used. Treatments should occur in the spring as soon as larvae are present.

In its native range, elm zigzag sawfly is considered a mild pest, natural predators and parasitoids are known but are relatively unsuccessful at containing the populations.

Pesticide application has been effective in controlling larva in other countries, but the pesticides available for use in these countries are not specific to the sawfly larvae, and will kill other insect species. Therefore, pesticide applications are likely to have significant effects on other invertebrates inhabiting the elm trees.

The impact of predators and parasitoids is also largely unknown, and there are very few observations of predation on the sawfly’s larvae or pupae. The parasitoid fauna associated with the sawfly is therefore poorly understood, and further research is needed before any potential for control by natural means, such as predators and parasites, can be known.

The most effective measures for slowing the spread of this pest are:

  • limiting movements of elm plants to the minimum number and distance necessary;
  • inspecting elm plants, and any soil and leaf litter with them, upon receiving them, before moving them on, and again before planting them;
  • cleaning and disinfecting equipment, machinery and vehicles used in tree and forestry operations before moving to new sites;
  • destroying elm material arising from pruning or felling – on site if possible, or if it is not possible, covering it securely before moving it to a place of destruction or burial.

Vermont Distribution

Elm zigzag sawfly has been confirmed in Vermont. View US distribution map (updated January 2023).