hemlock woolly adelgid

An invasive insect is threatening the destruction of Ontario forests

A problematic invasive forest species was recently detected in Ontario by the Canadian Food Inspection Agency (CFIA), and here's what you need to know about the pesky critters. 

Hemlock Woolly Adelgid (HWA) is an aphid-like insect native to Eastern Asia that attacks and kills hemlock trees by feeding on nutrient and water storage cells at the base of needles. 

You might recognize the insect's egg sacs, which resemble cotton balls or clumps of snow are located at the base of hemlock tree needles. The species is currently wreaking havoc and causing damage across Canada, including some areas of British Columbia, Nova Scotia, and Ontario. 

The species can be spread by wind, animals and human movement of nursery stock, logs, firewood and other wood products, which makes early detection key in protecting forests from further degradation. 

The invasive insects can also have devastating impacts on birds and other wildlife species that rely on hemlock trees to provide nutrients, soil stability and a unique habitat. 

According to the CFIA, the species was most recently detected in Port Colborne in 2024, as well as in Lincoln, Haldimand County and Hamilton in 2023. 

The agency works closely with federal, provincial, and industry partners to manage the spread of the pest, including issuing several Hemlock Woolly Adelgid Infested Place Orders

Anyone who wants to move particular natural items — such as hemlock, yeddo spruce, tiger-tail spruce, plants for planting, forest products with bark attached, dried branches, fresh decorative wreaths and firewood products out of infested areas — requires a movement certificate from the CFIA. 

If you spot the invasive species, make sure to report it to the CFIA, and always make sure to use firewood that is local or kiln-dried (certified pest-free) to prevent the spread of pests. 

Lead photo by

Jay Ondreicka/Shutterstock


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