Hemlock woolly adelgid (HWA) (Adelges tsugae) is a tiny aphid-like insect that feeds on hemlock tree needles (Tsuga spp.). HWA is native to Asia and northwestern North America, where natural predators keep the population in check. Eastern hemlock trees in Toronto are highly susceptible to damage from feeding and can kill the tree in 4 -15 years.
In Eastern North America, HWA was first recorded in 1951 in Virginia. The first established populations of HWA in Canada were found in Nova Scotia in 2017. In Ontario, two established populations were found in Niagara Region in 2019. There are now known pockets of HWA in Grafton, Ontario. In spring, 2025, HWA was found within the City of Toronto, in Rouge National Urban Park and in Morningside Park.
The City is working collaboratively with external partners and stakeholders, including the Canadian Food Inspection Agency, the Invasive Species Centre, Parks Canada (staff at Rouge National Urban Park) and the Canadian Forestry Service to continue monitoring for HWA, explore options for treatment and public education.
Don't move firewood. Always buy firewood locally or choose kiln dried firewood to avoid spreading pests to new areas
Clean your gear. Wash boots, clothes, and equipment after visiting hemlock forests to reduce the spread of HWA to new areas.
Stay Alert. If you see signs of HWA in the hemlock trees around you, report suspected sightings immediately to the Canadian Food Inspection Agency (CFIA): Contact Us - Canadian Food Inspection Agency
For more information about HWA, please visit the City of Toronto website.