Hemlock Woolly Adelgid (HWA)

Hemlock Woolly Adelgid

Hemlock Woolly Adelgid (HWA) is a small insect, similar to a beetle (aphid), which originates from parts of Asia. It infects a number of species of Hemlock trees and feeds on nutrient and water-storing cells of the tree. Heavy infestations can lead to tree mortality and, in some cases to our south, whole forests of Hemlock have been killed.

HWA was discovered in southern Nova Scotia in 2017 and since its arrival, HWA has been slowly moving northward, infesting populations of our native Eastern Hemlock. It was identified in the Halifax Regional Municipality in August 2023. 

What to look for

HWA presents itself most notably as small white woolly egg masses, 2-4 mm in diameter. These masses can be found on the underside of the needles, where they attach to branches. It is present year round, but most visible November through July. HWA does not affect fir, spruce or pine trees - three other common conifers in the municipality. 

Hemlock tree

How to identify Eastern Hemlock

Eastern Hemlock is an evergreen tree and often one of the largest trees in the forest. It is long lived and prefers cooler, moist sites along streams and lakes. It is common in forests across Nova Scotia, including the municipality. In some forests, it can be the dominant species (such as Hemlock Ravine Park).

Hemlock trees have needles that are dark green, short, flat and blunt. If you can roll the needles in your hand, it’s not a hemlock; if the tips of the needles are sharp, it’s also not a hemlock. 

A notable characteristic of the Eastern Hemlock is that, particularly when young, the tips of the branches and the very tip of the tree may droop or ‘weep.’ 

Hemlock trees also tolerate shade and can often be found in the underwood of mature forests, in river valleys or bottoms of slopes.  


Eastern Hemlock is not a significant forest species in Nova Scotia from a timber use perspective; but this has meant that it has often been left on the landscape to mature, meaning many of the larger mature trees in the forests of Nova Scotia may often include Hemlock trees. 

Despite its limited use economically, it is important environmentally, impacting local ecosystems, recreation and esthetics; not to mention the social and cultural impacts to communities that have coexisted with these trees for thousands of years.

The tendency of Hemlock trees to grow along rivers and streams also gives it an importance in shading these watercourses, a necessity of cold-water fish such as brook trout and salmon.

Additional Resources

If you suspect you may have HWA on your property, you can contact the Canadian Food Inspection Agency, or visit their web page for more information.