Citizen Science Tracks Elm Zigzag Sawfly

The invasive elm zigzag sawfly (Aproceros leucopoda) has spread rapidly into Eastern Ontario during 2021 since being discovered in Quebec in 2020. A citizen science observation made in July 2020 and posted in iNaturalist marked the first documented occurrence of the pest in Canada and North America. Elm Zigzag Sawfly is native to east Asia and had previously been detected in Europe almost 20 years ago, where it has spread rapidly since then.

The feeding track of elm zigzag sawfly (Aproceros leucopoda).  Photo by O. Clarkin.
The feeding track of elm zigzag sawfly (Aproceros leucopoda). Photo by O. Clarkin.

Trees Canadensis’ Owen Clarkin has been tracking the progress of the elm zigzag sawfly throughout the summer and fall of 2021. As of 5 October 2021, Owen has recorded 189 of the 198 observations in Ontario. The pest moved west, from the eastern border with Quebec, Voyageur Provincial Park, and Cornwall through Ottawa to Dunrobin, Carleton Place, and Brockville.

Elm zigzag sawfly observations in Eastern Ontario during 2021.
198 elm zigzag sawfly observations in Eastern Ontario as of 5 October 2021. Source: iNaturalist.

Already under threat from other non-native pest and disease introductions, elm trees in Ottawa have been in decline since Dutch elm disease reached the area in the 1970’s. The skeletons of dead elms are visible across rural landscapes in Eastern Ontario, reminding us of the magnificent shade trees that we have lost. Yet some survivors still stand, perhaps naturally resistant to disease. Adding yet another alien pest that defoliates weakened trees may be too much for our native elms to withstand.

The larval stage of the elm zigzag sawfly is the problem. The female sawfly lays eggs on elm leaves and seems well-adapted to Ulmus americana. Newly hatched larvae voraciously consume the leaves, leaving a characteristic zigzag feeding track that is easy to identify.

Elm zigzag sawfly larva devouring an elm tree leaf.  Photo by O. Clarkin.
Elm zigzag sawfly larva devouring an elm tree leaf. Photo by O. Clarkin.

The elm zigzag sawfly has the potential to expand quickly across Canada:

  • It reproduces rapidly. Four to six generations can occur from May to October.
  • It reproduces asexually. The females do not need male fertilization to lay viable eggs.
  • It travels quickly – up to 90 km in a year.
  • It survives cold temperatures – down to -30oC.

Véronique Martel, a research scientist and entomologist at the Canadian Forest Service (CFS), and colleagues recently published a paper that made use of citizen science data, including iNaturalist observations, to track the progress of elm zigzag sawfly.

Take Action

Citizen scientists can assist CFS and other scientists by recording their own elm zigzag sawfly observations in iNaturalist to document the spread of the pest across Canada. Look for the trademark zigzag track. Japanese beetles also eat elm leaves between the veins, but do not leave a zigzag pattern.


The Ottawa Field Naturalists’ Club (OFNC) and Trees Canadensis spearheaded the citizen science project to track the spread of elm zigzag sawfly in Eastern Ontario. Led by Owen Clarkin, head of the OFNC Conservation Committee, the initiative included contributions from: Elsa Clarkin, Gwen Clarkin, Jakob Mueller, Diane Lepage, Christine Hanrahan, Jonathan Mack, Fred Schueler, Henry Robertson, and J. Mason.

Véronique Martel and Spencer Monckton provided helpful information about elm zigzag sawfly in Quebec and North America in general.

Learn More

View Owen Clarkin’s elm zigzag sawfly observations in iNaturalist for photos of leaf damage and larvae.

Invasive Species Centre – Canada.  Elm Zigzag Sawfly. Description, life cycle, habitat.

Véronique Martel et al.  “Elm zigzag sawfly, Aproceros leucopoda (Hymenoptera: Argidae), recorded for the first time in North America through community science“. The Canadian Entomologist. 23 September 2021.   Recent information about the spread of Elm zigzag sawfly in Canada and the use of citizen science to track its progress, including citation of one of Owen Clarkin’s early iNaturalist observations.

Citizen scientist spots a newcomer on Canadian elm trees. National Research Council of Canada. September 2020.

American Elm – Endangered. International Union for Conservation of Nature.

Dutch Elm Disease. National Capital Commission.