Picture this: a person walks past a tree with a leaf that has been obviously chewed by an insect.

They snap a photo of a pretty distinctive zigzag pattern that it made and posts it on iNaturalist.ca. The person has no idea what it might be and hopes maybe the iNaturalist community might be able to help.

Observation by Alain Hogue

The observation catches the attention of an entomologist who then shows it to an expert in Germany and another in the United States. Turns out this random find is the discovery of the first ever occurrence of the invasive Elm Zigzag Sawfly in North America. As if elm trees needed another pest to deal with after Dutch Elm Disease having worked away on these trees since the 1940’s.

The agency in charge of invasive species that attack plants (the Canadian Food Inspection Agency, aka CFIA) caught wind of this find. In response, it set up monitoring traps and confirmed the presence of the insect. On the observation post, the Agency thanked the iNaturalist observer.

“We are looking into its distribution in Canada. iNaturalist community has been tremendously helpful!” ~Natural Resources Canada

Natural Resources Canada has published information about the Zigzag Sawfly and this find in their Simply Science magazine to encourage others to keep an eye out for this potential pest. This species naturally occurs in Asia and was found to be introduced in Europe in 2003, where it has since become established.

The Value of iNaturalist

This is iNaturalist in action. Its participants are helping Canada’s wildlife. Even a seemingly insignificant observation can lead to a major discovery.

Detecting new invasive species early on before they take hold is critical to curb their spread before they become unmanageable.

As for the observer, he has inspired others (including a scientist at the Montreal Insectarium) to take a second look at elm leaves. There are now 13 observations of the Elm Zigzag Sawfly in North America, all centered around southern Quebec.

We can all help track and curb the spread by checking any elm leaves you see and reporting these distinctive zigzag patterns using iNaturalist.ca or the free iNaturalist app.

Beyond that, all your observations contribute to the knowledge of Canadian biodiversity. You never know when one of your observations may turn out to be a momentous discovery.

Learn more or join iNaturalist.ca