HEMLOCK WOOLLY ADELGID: HAVE YOU SEEN ME?

April 24, 2026

Hemlock Woolly Adelgid (HWA) is an aphid-like invasive insect that attacks and kills Hemlock Trees by attaching to branches and feeding at the base of needles taking nutrients and sap.

Spring is peak time to spot HWA egg sacs, which look like tiny cotton balls found at the base of needles. Hemlock Trees can be found in shady, moist areas. Needles are dark yellowish-green, short, flat and flexible and are attached to the twig with a slender stalk.

HWA has not yet been sighted in York Region. Early detection is the most successful way to minimize the damage and cost of HWA.

York Region residents and visitors to the York Regional Forest (YRF) play a vital role in preventing the introduction and spread of HWA:

Avoid placing bird feeders near Hemlock Trees as birds can accidentally transport HWA to new locations
Brush off shoes, pants, clothes and pets after visiting trails and forests
Do not move branches or firewood as you could accidently spread HWA to areas that are not yet infested

Report suspected sightings of HWA egg sacs to the Canadian Food Inspection Agency by emailing @email, calling 647-790-1100 or through the online tool.

HWA facts

HWA (Adelges Tsugae) was first reported in the United States in 1951, where it was likely brought in on infested plant material from Japan
HWA is established in Ontario, mostly in Niagara Region, Northumberland County and the City of Hamilton, and was reported in Morningside Park in the City of Toronto and Rouge Urban National Park in Scarborough in 2025
HWA has no natural enemies in Canada to help keep its population under control
There is no known health hazard associated with this pest
Hemlock Trees are native to North America; Indigenous communities use the bark and needles to treat colds, coughs and fevers
A total of 377 hectares in 17 tracts contain Hemlock Trees in the YRF
The Region is monitoring for HWA in the YRF and encouraging partners including local cities and towns and conservation authorities to monitor Hemlock Trees on their respective properties.

In 2026, the Region will use the following monitoring tactics:

Slingshots and velcro balls to check for Hemlock Woolly Adelgid eggs high up in Hemlock Trees
Sticky traps to catch crawlers which are the size of a poppy seed and visible only under a microscope
3D-printed traps to collect HWA environmental DNA (eDNA) – genetic material shed by HWA into the environment

Additional information

For more information about HWA including what to look for, impacts and how you can help stop the spread visit york.ca/InvasiveSpecies