HEMLOCK WOOLLY ADELGID: HAVE YOU SEEN ME?

April 23, 2025
Hemlock Woolly Adelgid

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.

Quick 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 and Northumberland County and was recently reported in the City of Hamilton
  • 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 York Regional Forest and encouraging partners including local cities and towns and conservation authorities to monitor Hemlock Trees on their respective properties.

Additional information

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